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

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

Drilling holes in a bulk high-Tc superconductor enhances the oxygen annealing and the heat exchange with the cooling liquid. However, drilling holes also reduces the amount of magnetic flux that can be trapped in the sample. In this paper, we use the Bean model to study the magnetization and the current line distribution in drilled samples, as a function of the hole positions. A single hole perturbs the critical current flow over an extended region that is bounded by a discontinuity line, where the direction of the current density changes abruptly. We demonstrate that the trapped magnetic flux is maximized if the center of each hole is positioned on one of the discontinuity lines produced by the neighbouring holes. For a cylindrical sample, we construct a polar triangular hole pattern that exploits this principle; in such a lattice, the trapped field is ~20% higher than in a squared lattice, for which the holes do not lie on discontinuity lines. This result indicates that one can simultaneously enhance the oxygen annealing, the heat transfer, and maximize the trapped field

The scaling dimension of low lying Dirac eigenmodes and of the topological charge density

As a quantitative measure of localization, the inverse participation ratio of low lying Dirac eigenmodes and topological charge density is calculated on quenched lattices over a wide range of lattice spacings and volumes. Since different topological objects (instantons, vortices, monopoles, and artifacts) have different co-dimension, scaling analysis provides information on the amount of each present and their correlation with the localization of low lying eigenmodes.Comment: Lattice2004(topology), Fermilab, June 21 - 26, 2004; 3 pages, 3 figure

Euclidean Black Hole Vortices

We argue the existence of solutions of the Euclidean Einstein equations that correspond to a vortex sitting at the horizon of a black hole. We find the asymptotic behaviours, at the horizon and at infinity, of vortex solutions for the gauge and scalar fields in an abelian Higgs model on a Euclidean Schwarzschild background and interpolate between them by integrating the equations numerically. Calculating the backreaction shows that the effect of the vortex is to cut a slice out of the Euclidean Schwarzschild geometry. Consequences of these solutions for black hole thermodynamics are discussed.Comment: 24 page

Cosmic D-Strings and Vortons in Supergravity

Recent developments in string inspired models of inflation suggest that D-strings are formed at the end of inflation. Within the supergravity model of D-strings there are 2(n-1) chiral fermion zero modes for a D-string of winding n. Using the bounds on the relic vorton density, we show that D-strings with winding number n>1 are more strongly constrained than cosmic strings arising in cosmological phase transitions. The D-string tension of such vortons, if they survive until the present, has to satisfy 8\pi G_N \mu \lesssim p 10^{-26} where p is the intercommutation probability. Similarly, D-strings coupled with spectator fermions carry currents and also need to respect the above bound. D-strings with n=1 do not carry currents and evade the bound. We discuss the coupling of D-strings to supersymmetry breaking. When a single U(1) gauge group is present, we show that there is an incompatibility between spontaneous supersymmetry breaking and cosmic D-strings. We propose an alternative mechanism for supersymmetry breaking, which includes an additional U(1), and might alleviate the problem. We conjecture what effect this would have on the fermion zero modes.Comment: 11 page

Efficient analysis in planet transit surveys

With the growing number of projects dedicated to the search for extrasolar planets via transits, there is a need to develop fast, automatic, robust methods with a statistical background in order to efficiently do the analysis. We propose a modified analysis of variance (AoV) test particularly suitable for the detection of planetary transits in stellar light curves. We show how savings of labor by a factor of over 10 could be achieved by the careful organization of computations. Basing on solid analytical statistical formulation, we discuss performance of our and other methods for different signal-to-noise and number of observations.Comment: 7 pages, to be published in MNRAS, downloadable software from http://www.camk.edu.pl/~alex/#softwar

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

Minocycline treatment inhibits microglial activation and alters spinal levels of endocannabinoids in a rat model of neuropathic pain

Activation of spinal microglia contributes to aberrant pain responses associated with neuropathic pain states. Endocannabinoids (ECs) are present in the spinal cord, and inhibit nociceptive processing; levels of ECs may be altered by microglia which modulate the turnover of endocannabinoids in vitro. Here, we investigate the effect of minocycline, an inhibitor of activated microglia, on levels of the endocannabinoids anandamide and 2-arachidonoylglycerol (2-AG), and the related compound N-palmitoylethanolamine (PEA), in neuropathic spinal cord. Selective spinal nerve ligation (SNL) in rats resulted in mechanical allodynia and the presence of activated microglia in the ipsilateral spinal cord. Chronic daily treatment with minocycline (30 mg/kg, ip for 14 days) significantly reduced the development of mechanical allodynia at days 5, 10 and 14 post-SNL surgery, compared to vehicle-treated SNL rats (P < 0.001). Minocycline treatment also significantly attenuated OX-42 immunoreactivity, a marker of activated microglia, in the ipsilateral (P < 0.001) and contralateral (P < 0.01) spinal cord of SNL rats, compared to vehicle controls. Minocycline treatment significantly (P < 0.01) decreased levels of 2-AG and significantly (P < 0.01) increased levels of PEA in the ipsilateral spinal cord of SNL rats, compared to the contralateral spinal cord. Thus, activation of microglia affects spinal levels of endocannabinoids and related compounds in neuropathic pain states

Bremsstrahlung in the gravitational field of a cosmic string

In the framework of QED we investigate the bremsstrahlung process for an electron passing by a straight static cosmic string. This process is precluded in empty Minkowski space-time by energy and momentum conservation laws. It happens in the presence of the cosmic string as a consequence of the conical structure of space, in spite of the flatness of the metric. The cross section and emitted electromagnetic energy are computed and analytic expressions are found for different energies of the incoming electron. The energy interval is divided in three parts depending on whether the energy is just above electron rest mass $M$, much larger than $M$, or exceeds $M/\delta$, with $\delta$ the string mass per unit length in Planck units. We compare our results with those of scalar QED and classical electrodynamics and also with conic pair production process computed earlier.Comment: 21 pages, to appear in Phys. Rev. D., KONS-RGKU-94-0

A new fireworm (Amphinomidae) from the Cretaceous of Lebanon identified from three-dimensionally preserved myoanatomy

© 2015 Parry et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. The attached file is the published version of the article