Modification of the trapped field in bulk high-temperature superconductors as a result of the drilling of a pattern of artificial columnar holes

The trapped magnetic field is examined in bulk high-temperature superconductors that are artificially drilled along their c-axis. The influence of the hole pattern on the magnetization is studied and compared by means of numerical models and Hall probe mapping techniques. To this aim, we consider two bulk YBCO samples with a rectangular cross-section that are drilled each by six holes arranged either on a rectangular lattice (sample I) or on a centered rectangular lattice (sample II). For the numerical analysis, three different models are considered for calculating the trapped flux: (i), a two-dimensional (2D) Bean model neglecting demagnetizing effects and flux creep, (ii), a 2D finite-element model neglecting demagnetizing effects but incorporating magnetic relaxation in the form of an E-J power law, and, (iii), a 3D finite element analysis that takes into account both the finite height of the sample and flux creep effects. For the experimental analysis, the trapped magnetic flux density is measured above the sample surface by Hall probe mapping performed before and after the drilling process. The maximum trapped flux density in the drilled samples is found to be smaller than that in the plain samples. The smallest magnetization drop is found for sample II, with the centered rectangular lattice. This result is confirmed by the numerical models. In each sample, the relative drops that are calculated independently with the three different models are in good agreement. As observed experimentally, the magnetization drop calculated in the sample II is the smallest one and its relative value is comparable to the measured one. By contrast, the measured magnetization drop in sample (1) is much larger than that predicted by the simulations, most likely because of a change of the microstructure during the drilling process.Comment: Proceedings of EUCAS 09 conferenc

Pulsed-field magnetization of drilled bulk high-temperature superconductors: flux front propagation in the volume and on the surface

We present a method for characterizing the propagation of the magnetic flux in an artificially drilled bulk high-temperature superconductor (HTS) during a pulsed-field magnetization. As the magnetic pulse penetrates the cylindrical sample, the magnetic flux density is measured simultaneously in 16 holes by means of microcoils that are placed across the median plane, i.e. at an equal distance from the top and bottom surfaces, and close to the surface of the sample. We discuss the time evolution of the magnetic flux density in the holes during a pulse and measure the time taken by the external magnetic flux to reach each hole. Our data show that the flux front moves faster in the median plane than on the surface when penetrating the sample edge; it then proceeds faster along the surface than in the bulk as it penetrates the sample further. Once the pulse is over, the trapped flux density inside the central hole is found to be about twice as large in the median plane than on the surface. This ratio is confirmed by modelling

3D finite‐element modeling for the magnetization of bulk high‐Tc drilled superconductors

Article associé : Numerical simulation of the magnetization of high-temperature superconductors: a 3D finite element method using a single time-step iteratio

Hole lattice influence on the magnetization of drilled superconductors

Article associé : Bulk high-Tc superconductors with drilled holes: how to arrange the holes to maximize the trapped magnetic flux

The predictive value of pain event-related potentials for the clinical experience of pain

Event-related potentials (ERPs) have been found to be related to subjective experience of experimental pain. But how are they related to the subjective experience of clinical pain? The current study investigated the predictive value of the pain ERP for the subjective experience of clinical pain. Event-related potentials in response to experimental pain were measured in 75 chronic low back pain sufferers. In addition, a two-week registration to note the amount of pain they experienced in daily life was done. The results demonstrate that the N2-component at Cz and C4 of the pain ERP (contralateral to the side of the stimulation) were significant predictors of clinical pain, and even stronger predictors than the accompanying subjective ratings of experimental pain. Thus, it seems promising to use event-related potentials as a more objective measure to make predictions about a person's likely pain experience in daily life

Numerical simulation of the magnetization of high-temperature superconductors: 3D finite element method using a single time-step iteration

We make progress towards a 3D finite-element model for the magnetization of a high temperature superconductor (HTS): We suggest a method that takes into account demagnetisation effects and flux creep, while it neglects the effects associated with currents that are not perpendicular to the local magnetic induction. We consider samples that are subjected to a uniform magnetic field varying linearly with time. Their magnetization is calculated by means of a weak formulation in the magnetostatic approximation of the Maxwell equations (A-phi formulation). An implicit method is used for the temporal resolution (Backward Euler scheme) and is solved in the open source solver GetDP. Picard iterations are used to deal with the power law conductivity of HTS. The finite element formulation is validated for an HTS tube with large pinning strength through the comparison with results obtained with other well-established methods. We show that carrying the calculations with a single time-step (as opposed to many small time-steps) produce results with excellent accuracy in a drastically reduced simulation time. The numerical method is extended to the study of the trapped magnetization of cylinders that are drilled with different arrays of columnar holes arranged parallel to the cylinder axis

Comparing symptoms of depression and anxiety as predictors of cardiac events and increased health care consumption after myocardial infarction

AbstractObjectivesWe sought to compare symptoms of depression and anxiety as predictors of incomplete recovery after a first myocardial infarction (MI).BackgroundDepressive symptoms have been related to post-MI mortality and health care consumption, but little is known about the effect of anxiety. We wanted to examine the effect of emotional distress on health care consumption and whether depressive symptomatology is a better predictor of prognosis than anxiety.MethodsSubjects were 318 men (mean age 58 years) who completed the depression, anxiety, and hostility scales from the 90-item symptom check list after they survived a first MI.ResultsAfter an average follow-up of 3.4 years, there were 25 cardiac events (fatal or non-fatal MI). Symptoms of both depression (hazard ratio [HR] 2.32, 95% confidence interval [CI] 1.04 to 5.18; p = 0.039) and anxiety (HR 3.01, 95% CI 1.20 to 7.60; p = 0.019) were associated with cardiac events, adjusting for age, left ventricular ejection fraction, and use of antidepressants. However, a multivariate analysis including all three negative emotions indicated that symptoms of anxiety (HR 2.79, 95% CI 1.11 to 7.03; p = 0.029) explained away the relationship between depressive symptoms and cardiac events. Regarding health care consumption, anxiety (OR 2.00, 95% CI 1.24 to 3.22; p = 0.005), but not depression/hostility, was a predictor of cardiac rehospitalization and frequent visits at the cardiac outpatient clinic.ConclusionsSymptoms of depression and anxiety were associated with cardiac events. Anxiety was an independent predictor of both cardiac events and increased health care consumption and accounted for the relationship between depressive symptoms and prognosis. Symptoms of anxiety need to be considered in the risk stratification and treatment of post-MI patients