Universal linear relations between susceptibility and Tc in cuprates

We developed an experimental method for measuring the intrinsic susceptibility \chi of powder of cuprate superconductors in the zero field limit using a DC-magnetometer. The method is tested with lead spheres. Using this method we determine \chi for a number of cuprate families as a function of doping. A universal linear (and not proportionality) relation between Tc and \chi is found. We suggest possible explanations for this phenomenon.Comment: Accepted for publication in PR

Propagation of uncertainty in a rotating pipe mechanism to generate an impinging swirling jet flow for heat transfer from a flat plate

In Computational Fluid Dynamics (CFD) studies composed of the coupling of different simulations, the uncertainty in one stage may be propagated to the following stage and affect the accuracy of the prediction. In this paper, a framework for uncertainty quantification in the computational heat transfer by forced convection is applied to the two-step simulation of the mechanical design of a swirling jet flow generated by a rotating pipe (Simulation 1) impinging on a flat plate (Simulation 2). This is the first probabilistic uncertainty analysis on computational heat transfer by impinging jets in the literature. The conclusion drawn from the analysis of this frequent engineering application is that the simulated system does not exhibit a significant sensitivity to stochastic variations of model input parameters, over the tested uncertainty ranges. Additionally, a set of non-linear regression models for the stochastic velocity and turbulent profiles for the pipe nozzle are created and tested, since impinging jets for heat transfer at Reynolds number of Re = 23000 are very frequent in the literature, but stochastic inlet conditions have never been provided. Numerical results demonstrate a negligible difference in the predicted convective heat transfer with respect to the use of the profiles simulated via CFD. These suggested surrogate models can be directly embedded onto other engineering applications (e.g. arrays of jets, jet flows impinging on plates with different shapes, inlet piping in combustion, chemical mixing, etc.) in which a realistic swirling flow under uncertainty can be of interest

Effects of relaxation in levitating superconductors

The effect of the magnetic flux creep on the levitation stability of high-temperature superconductors was studied. It was shown experimentally that under a unipolar magnetization the levitation force decreased at a logarithmic velocity characteristic of the creep process. If the current structure was bi- or multi-polar one, which was formed in a sample exposed to a reversing external magnetic field, the force remained unchanged during a certain period of time. The theory of relaxation of magnetization and force for a partial and full penetration of the critical state was considered. It was shown that relaxation decelerated sharply if the region with a current producing the main magnetization was far from the superconductor surface. A concept of an open and internal magnetic relaxation was introduced. The time of the internal relaxation for different reverse depths was estimated. The calculated values approached the experimental values of the levitation stabilization time. © 2002 Elsevier Science Ltd. All rights reserved

Quantifying uncertainty in Gulf of Mexico forecasts stemming from uncertain initial conditions

Polynomial Chaos (PC) methods are used to quantify the impacts of initial conditions uncertainties on oceanic forecasts of the Gulf of Mexico circulation. Empirical Orthogonal Functions are used as initial conditions perturbations with their modal amplitudes considered as uniformly distributed uncertain random variables. These perturbations impact primarily the Loop Current system and several frontal eddies located in its vicinity. A small ensemble is used to sample the space of the modal amplitudes and to construct a surrogate for the evolution of the model predictions via a nonintrusive Galerkin projection. The analysis of the surrogate yields verification measures for the surrogate's reliability and statistical information for the model output. A variance analysis indicates that the sea surface height predictability in the vicinity of the Loop Current is limited to about 20 days. Key Points Polynomial Chaos were used to quantify uncertainties in oceanic forecasts caused by initial conditions uncertainties Uncertainty in the strength of a frontal eddy controls uncertainty in the forecast Variance analysis suggests a loss of predictability in SSH in the Loop Current pinch‐off region after day 2