25 research outputs found
Properties of recent IBAD-MOCVD Coated Conductors relevant to their high field, low temperature magnet use
BaZrO3 (BZO) nanorods are now incorporated into production IBAD-MOCVD coated
conductors. Here we compare several examples of both BZO-free and
BZO-containing coated conductors using critical current (Ic) characterizations
at 4.2 K over their full angular range up to fields of 31 T. We find that BZO
nanorods do not produce any c-axis distortion of the critical current density
Jc(theta) curve at 4.2 K at any field, but also that pinning is nevertheless
strongly enhanced compared to the non-BZO conductors. We also find that the
tendency of the ab-plane Jc(theta) peak to become cusp-like is moderated by BZO
and we define a new figure of merit that may be helpful for magnet design - the
OADI (Off-Axis Double Ic), which clearly shows that BZO broadens the ab-plane
peak and thus raises Jc 5-30{\deg} away from the tape plane, where the most
critical approach to Ic occurs in many coil designs. We describe some
experimental procedures that may make critical current Ic tests of these very
high current tapes more tractable at 4.2 K, where Ic exceeds 1000 A even for 4
mm wide tape with only 1 micron thickness of superconductor. A positive
conclusion is that BZO is very beneficial for the Jc characteristics at 4.2 K,
just as it is at higher temperatures, where the correlated c-axis pinning
effects of the nanorods are much more obvious
Theoretical Description of Nearly Discontinuous Transition in Superconductors with Paramagnetic Depairing
Based on a theoretical argument and Monte Carlo simulations of a
Ginzburg-Landau model derived microscopically, it is argued that, in type-II
superconductors where {\it both} the paramagnetic {\it and} orbital depairings
are important, a strong first-order transition (FOT) at expected in
the mean field (MF) approximation never occurs in real systems and changes due
to the fluctuation into a crossover. The present result explains why a {\it
nearly} discontinuous crossover at with {\it no} intrinsic hysteresis
is observed only in a clean superconducting material with a singlet pairing and
a high condensation energy such as CeCoIn.Comment: Publication version. See cond-mat/0306060 regarding a corresponding
long pape
Flux quanta driven by high-density currents in low-impurity V3Si and LuNi2B2C: free flux flow and flux-core size effect
High density direct currents (DC) are used to drive flux quanta via the
Lorentz force towards a highly ordered "free flux flow" (FFF) dynamic state,
made possible by the weak-pinning environment of high-quality, single-crystal
samples of two low-Tc superconducting compounds, V3Si and LuNi2B2C. We report
the effect of the magnetic field-dependent fluxon core size on flux flow
resistivity rho_f. Much progress has been made in minimizing the technical
challenges associated with the use of high currents. Attainment of a FFF phase
is indicated by the saturation at highest currents of flux-flow dissipation
levels that are well below the normal state resistance and have field-dependent
values. The field dependence of the corresponding rho_f is shown to be
consistent with a prediction based on a model for the decrease of flux core
size at higher fields in weak-coupling BCS s-wave materials.Comment: More empirical treatment of the magnetoresistive correction of V3Si
data by additional measurement and analysis (involving two new coauthors,
Favreau and Henderson). End result is the same, making for a stronger
manuscrip
Loss of ATM kinase activity leads to embryonic lethality in mice
Ataxia telangiectasia (A-T) mutated (ATM) is a key deoxyribonucleic acid (DNA) damage signaling kinase that regulates DNA repair, cell cycle checkpoints, and apoptosis. The majority of patients with A-T, a cancer-prone neurodegenerative disease, present with null mutations in Atm. To determine whether the functions of ATM are mediated solely by its kinase activity, we generated two mouse models containing single, catalytically inactivating point mutations in Atm. In this paper, we show that, in contrast to Atm-null mice, both D2899A and Q2740P mutations cause early embryonic lethality in mice, without displaying dominant-negative interfering activity. Using conditional deletion, we find that the D2899A mutation in adult mice behaves largely similar to Atm-null cells but shows greater deficiency in homologous recombination (HR) as measured by hypersensitivity to poly (adenosine diphosphate-ribose) polymerase inhibition and increased genomic instability. These results may explain why missense mutations with no detectable kinase activity are rarely found in patients with classical A-T. We propose that ATM kinase-inactive missense mutations, unless otherwise compensated for, interfere with HR during embryogenesis
Comparative mitogenomic analysis of the superfamily Pentatomoidea (Insecta: Hemiptera: Heteroptera) and phylogenetic implications
On the structure of the aedeagus of shield bugs (Heteroptera, Pentatomidae): III. Subfamily asopinae
Flux quanta driven by high-density currents in low-impurity V3Si and LuNi2B2C: Free flux flow and fluxon-core size effect
High-density direct currents are used to drive flux quanta via the Lorentz force toward a highly ordered "free flux flow" (FFF) dynamic state, made possible by the weak-pinning environment of high-quality, single-crystal samples of two low-T-c superconducting compounds, V3Si and LuNi2B2C. We report the effect of the magnetic field-dependent fluxon-core size on flux flow resistivity rho(f). Much progress has been made in minimizing the technical challenges associated with the use of high currents. Attainment of a FFF phase is indicated by the saturation at highest currents of flux flow dissipation levels that are well below the normal-state resistance and have field-dependent values. The field dependence of the corresponding rho(f) is shown to be consistent with a prediction based on a model for the decrease of fluxon-core size at higher fields in weak-coupling BCS s-wave materials.This article is published as Gapud, Albert A., S. Moraes, R. P. Khadka, P. Favreau, C. Henderson, P. C. Canfield, V. G. Kogan et al. "Flux quanta driven by high-density currents in low-impurity V 3 Si and LuNi 2 B 2 C: Free flux flow and fluxon-core size effect." Physical Review B 80, no. 13 (2009): 134524.
DOI: 10.1103/PhysRevB.80.134524.
Copyright 2009 American Physical Society.
Posted with permission