Temperature dependence in random matrix models with pairing condensates

We address a number of issues raised by a manuscript of Klein, Toublan, and Verbaarschot (hep-ph/0405180) in which the authors introduce a random matrix model for QCD with two colors, two flavors, and fermions in the fundamental representation. Their inclusion of temperature terms differs from the approach adopted in previous work on this problem (Phys. Rev. D 64, 074016 (2001).) We demonstrate that the two approaches are related by a transformation that leaves the thermodynamic potential invariant and which therefore has no effect on physical observables.Comment: 8 pages, revtex4. v2: typos corrected in reference

Study of Conduction Mechanisms in Antistatic Felts at the Mesoscopic Scale

peer reviewedThis work is part of a project that deals with the optimization of the quantity and the nature of conductive fibers in antistatic felts used for filtering and sieving powders. Our research concerns the electrical properties at the mesoscopic scale. It aims at determining the conduction mechanisms and the distribution of the electric potential at the scale of the distance between the conductive fibers. In this paper, current-voltage (I-V) measurement results are presented and discussed. X-ray microtomography is used to obtain the geometry of the conductive fibers inside the felts before and after these I-V tests. The studied textile material is based on polyester fibers and stainless steel conductive fibers.Nouvelle conception de filtres textiles antistatique

Magnetic shielding properties of high- Tc superconducting hollow cylinders: model combining experimental data for axial and transverse magnetic field configurations

peer reviewedMagnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77 K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10 uT s[?]1 and 10 mT s[?]1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n', is found between Blim and dBapp/dt. The values of n' are nearly the same for both configurations. We show that the main features of the curves Bin(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)[?]1). In particular, a linear relationship between the measured n'-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields

What Formulation Should One Choose for Modeling a 3D HTS Magnet Motor Pole with a Ferromagnetic Material?

We discuss the relevance of several finite-element formulations for nonlinear systems containing high-temperature superconductors (HTS) and ferromagnetic materials (FM), in the context of a 3D motor pole model. The formulations are evaluated in terms of their numerical robustness and efficiency. We propose a coupled h-phi-a-formulation as an optimal choice. While maintaining a low number of degrees of freedom, this formulation guarantees a robust resolution and strongly reduces the number of iterations required for handling the nonlinearities of HTS and FM compared to standard formulations

What Formulation Should One Choose for Modeling a 3D HTS Motor Pole with Ferromagnetic Materials?

peer reviewedWe discuss the relevance of several finite-element formulations for nonlinear systems containing high-temperature superconductors (HTS) and ferromagnetic materials (FM), in the context of a 3D motor pole model. The formulations are evaluated in terms of their numerical robustness and efficiency. We propose a coupled h-phi-a-formulation as an optimal choice, modeling the problem with an a-formulation in the FM and an h-phi-formulation in the remaining domains. While maintaining a low number of degrees of freedom, the h-phi-a-formulation guarantees a robust resolution and strongly reduces the number of iterations required for handling the nonlinearities of HTS and FM compared to standard formulations

2D FEM Calculation of AC Losses in Twisted Superconductors with a Helicoidal Transformation

We propose a Helicoidal Transformation for 2D Finite Element Method (FEM) calculation of AC losses in twisted conductors. The method is based on a helicoidal change of variables to transform the originally 3D problem into an equivalent 2D problem. For obtaining the critical state in superconductor we use the h-φ-formulation and E-J power law. The method is well suited for geometries with a helicoidal symmetry and we present the magnetic response and Joule losses of multifilamentary twisted wire in conducting matrix and CORC cable with a non-conducting core

3D Finite Element Models of Stacked Tapes Magnetic Shields

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SPICE-Circuit Simulation of the Electrical Response of a Semiconductor Membrane to a Single-Stranded DNA Translocating Through a Nanopore

peer reviewedIn this paper, we describe a circuit-element model for the electric detection of biomolecules in translocation through a nanopore in a semiconductor-oxide-semiconductor (SOS) membrane. The biomolecules are simulated as a superposition of individual charges moving through the nanopore and inducing a charge variation on the membrane electrodes that is modeled as a current source. The SOS membrane is discretized into interconnected elementary circuit elements. The model is tested on the translocation of 11 base single-stranded C3AC7 DNA molecule, for which the electric signal shows good qualitative agreement with the multiscale device approach of Gracheva et al., while quantifying the low-pass filtering in the membrane. Overall, the model confirms the possibility of identifying the sequence of the DNA bases electrically

Design of a superconducting magnetic shield closed on both ends for a high-sensitivity particle detector

peer reviewedThis work deals with the numerical design of a high-efficiency superconducting magnetic shield required for a high-sensitivity particle detector. This research was carried out in the context of the ‘ABRACADABRA’ project aiming at detecting hypothetical elementary particles called axions. Axions are promising candidates to explain the particle nature of the dark matter. The detector relies on a SQUID for measuring the ultra-small oscillating magnetic field resulting from the interaction between the axions and a toroidal DC field. A magnetic shield is mandatory to reduce the ambient magnetic field noise. Given the operating temperature (~ 1.2 K), the shield is made of type-I superconductor. In this work we use numerical modelling to determine the best topology for the shield and its ability to screen both axial and transverse fields. Amongst the geometries investigated (tubes or ‘swiss-rolls’ closed on both ends) the best results are obtained with two semi-closed tubes inserted in one another. This geometry is close to the shield of the final prototype, made of two closed Cu tubes, spin-coated with Sn (Tc = 3.72 K) and welded shut