Search results for " surface"
showing 10 items of 2838 documents
Evidence for Multiband Superconductivity in the Heavy Fermion CompoundUNi2Al3
2004
Epitaxial thin films of the heavy fermion superconductor UNi2Al3 with Tc(max)=0.98 K were investigated. The transition temperature Tc depends on the current direction which can be related to superconducting gaps opening at different temperatures. Also the influence of the magnetic ordering at TN approximately 5 K on R(T) is strongly anisotropic, indicating different coupling between the magnetic moments and itinerant charge carriers on the multisheeted Fermi surface. The upper critical field Hc2(T) suggests an unconventional spin-singlet superconducting state.
The influence of topological phase transition on the superfluid density of overdoped copper oxides
2017
We show that a topological quantum phase transition, generating flat bands and altering Fermi surface topology, is a primary reason for the exotic behavior of the overdoped high-temperature superconductors represented by $\rm La_{2-x}Sr_xCuO_4$, whose superconductivity features differ from what is described by the classical Bardeen-Cooper-Schrieffer theory [J.I. Bo\^zovi\'c, X. He, J. Wu, and A. T. Bollinger, Nature 536, 309 (2016)]. We demonstrate that 1) at temperature $T=0$, the superfluid density $n_s$ turns out to be considerably smaller than the total electron density; 2) the critical temperature $T_c$ is controlled by $n_s$ rather than by doping, and is a linear function of the $n_s$…
Differential Geometry of Curves and Surfaces
2001
The goal of this article is to present the relation between some differential formulas, like the Gauss integral for a link, or the integral of the Gaussian curvature on a surface, and topological invariants like the linking number or the Euler characteristic.
3D reconstruction of external and internal surfaces of transparent objects from polarization state of highlights
2014
A vision-based method is proposed to measure the 3D shape of external and internal surfaces (not accessible) of smooth transparent objects. Looking at the reflections of point sources on a specular surface with a polarimetric camera, we combine the measurements of two techniques: shape from distortion and shape from polarization. It permits us to recover the position and orientation of the specular surface for each detected point. The internal surface of transparent objects exhibiting as well a specular component, the same technique is used on the highlights coming from the back surface, taking into account the refraction by using polarimetric ray tracing.
Turbulent mixing and dispersion mechanisms over flexible and dense vegetation
2019
The present study investigates flow turbulence and dispersion processes in the presence of flexible and dense vegetation on the bed. The turbulent dispersion coefficients and the terms of the turbulent kinetic energy equation are determined by using data collected in a straight laboratory channel with living vegetation on the bed. Results show that the turbulent integral lengths assume an order of magnitude comparable to the stems’ characteristic dimension independently by the direction and the turbulence assumes an isotropic behavior. The coefficients of dispersion have a trend similar to that of the turbulent lengths and assume low values in the longitudinal, transversal and vertical dire…
Three-dimensional field distribution in the focal region of low-Fresnel-number axicons.
2006
Three-dimensional intensity and phase distributions generated by microaxicons are evaluated in the low-Fresnel-number regime. Apertured and nonapertured conical wavefronts may generate transverse patterns with notable deviations from the expected nondiffracting Bessel beam. First-order analytical expressions are proposed for the evaluation of the wave field produced by axicons of different Fresnel number in the focal region.
Spiral conical approximations to double reflection Wolter optics
2008
The design of a grazing incidence focusing optic obtained from a spiral approximation to multiple nested cones produces an annular image of a point source. The angular size of the annulus depends mainly on the pitch of the winding and the focal length. For a spiral conical approximation to Wolter optics, the effect is magnified by the double reflection. However, if the two conical spirals are wound one clock-wise and the other counter-clock-wise, then the aberration is partially compensated. We use a ray tracing code to evaluate advantages and disadvantages of this optical design for potential applications of a light weight optics technology based on plastic foils that we are currently inve…
Laser control in a bifurcating region
2006
We present a complete analysis of the laser control of a model molecular system using both optimal control theory and adiabatic techniques. This molecule has a particular potential energy surface with a bifurcating region connecting three potential wells which allows a variety of processes such as isomerization, tunnelling or implementation of quantum gates on one or two qubits. The parameters of the model have been chosen so as to reproduce the main features of H3CO which is a molecule-benchmark for such dynamics. We show the feasibility of different processes and we investigate their robustness against variations of laser field. We discuss the conditions under which each method of control…
Geometric Origin of the Tennis Racket Effect
2020
The tennis racket effect is a geometric phenomenon which occurs in a free rotation of a three-dimensional rigid body. In a complex phase space, we show that this effect originates from a pole of a Riemann surface and can be viewed as a result of the Picard-Lefschetz formula. We prove that a perfect twist of the racket is achieved in the limit of an ideal asymmetric object. We give upper and lower bounds to the twist defect for any rigid body, which reveals the robustness of the effect. A similar approach describes the Dzhanibekov effect in which a wing nut, spinning around its central axis, suddenly makes a half-turn flip around a perpendicular axis and the Monster flip, an almost impossibl…
Resolution and field of view improvement in digital holography using a VCSEL source array
2011
We describe a new implementation capable to produce superresolution (SR) and object field of view (FOV) improvement in digital lensless Fourier holography. The method provides synthetic aperture (SA) generation using angular multiplexing incoming from a Vertical Cavity Surface Emitting Laser (VCSEL) source array. SR imaging in a single exposure is obtained after proper digital processing of a multiplexed hologram coming from the incoherent addition of multiple sub-holograms, each one corresponding with a different source of the VCSEL array. FOV improvement in addition with SR imaging is achieved by recording a set of individual holograms obtained by sequential activation of the VCSEL source…