AC-Tolerant Multifilament Coated Conductors

We report the magnetization losses in an experimental multifilament coated conductor. A 4 mm wide and 10 cm long YBCO coated conductor was subdivided into eight 0.5 mm wide filaments by laser ablation and subjected to post-ablation treatment. As the result, the hysteresis loss was reduced, as expected, in proportion to the width of the filaments. However, the coupling loss was reduced dramatically, and became practically negligible, in the range of a sweep rate up to 20 T/s. This represents a drastic improvement on previous multifilament conductors in which often the coupling losses became equal to the hysteresis loss at a sweep rate as low as 3-4 T/s. These results demonstrate that there is an effective and practical way to suppress coupling losses in coated multifilament conductors.Comment: This paper is based on a talk given at 2006 Applied Superconductivity Conference in Seattle, WA (August 27-September 1, 2006). To be published in IEEE Trans. Appl. Superconductivit

The bergman kernel method for the numerical conformal mapping of simply connected domains

A numerical method for the conformal mapping of simply-connected domains onto the unit disc is considered. The method is based on the use of the Bergman kernel function of the domain. It is shown that, for a successful application, the basis of the series representation of the kernel must include terms that reflect the main singular behaviour of the kernel in the complement of the domain

Hurewicz Theorem for Assouad-Nagata dimension

Given a function $f\colon X\to Y$ of metric spaces, its {\it asymptotic dimension} \asdim(f) is the supremum of \asdim(A) such that $A\subset X$ and \asdim(f(A))=0. Our main result is \begin{Thm} \label{ThmAInAbstract} \asdim(X)\leq \asdim(f)+\asdim(Y) for any large scale uniform function $f\colon X\to Y$. \end{Thm} \ref{ThmAInAbstract} generalizes a result of Bell and Dranishnikov in which $f$ is Lipschitz and $X$ is geodesic. We provide analogs of \ref{ThmAInAbstract} for Assouad-Nagata dimension $\dim_{AN}$ and asymptotic Assouad-Nagata dimension \ANasdim. In case of linearly controlled asymptotic dimension \Lasdim we provide counterexamples to three questions in a list of problems of Dranishnikov. As an application of analogs of \ref{ThmAInAbstract} we prove \begin{Thm} \label{ThmBInAbstract} If $1\to K\to G\to H\to 1$ is an exact sequence of groups and $G$ is finitely generated, then \ANasdim (G,d_G)\leq \ANasdim (K,d_G|K)+\ANasdim (H,d_H) for any word metrics metrics $d_G$ on $G$ and $d_H$ on $H$. \end{Thm} \ref{ThmBInAbstract} extends a result of Bell and Dranishnikov for asymptotic dimension

Non-autonomous Hamiltonian systems related to highest Hitchin integrals

We describe non-autonomous Hamiltonian systems coming from the Hitchin integrable systems. The Hitchin integrals of motion depend on the W-structures of the basic curve. The parameters of the W-structures play the role of times. In particular, the quadratic integrals dependent on the complex structure (W_2-structure) of the basic curve and times are coordinate on the Teichmuller space. The corresponding flows are the monodromy preserving equations such as the Schlesinger equations, the Painleve VI equation and their generalizations. The equations corresponding to the highest integrals are monodromy preserving conditions with respect to changing of the W_k-structures (k>2). They are derived by the symplectic reduction from the gauge field theory on the basic curve interacting with W_k-gravity. As by product we obtain the classical Ward identities in this theory.Comment: 21 pages,Latex, Contribution in the Proceedings "International Seminar on Integrable systems". In memoriam Mikail V. Saveliev. Bonn, February, 199

Normal zone in YBa2Cu3O6+xYBa_2Cu_3O_{6+x}-coated conductors

We consider the distribution of an electric field in YBCO-coated conductors for a situation in which the DC transport current is forced into the copper stabilizer due to a weak link -- a section of the superconducting film with a critical current less than the transport current. The electric field in the metal substrate is also discussed. The results are compared with recent experiments on normal zone propagation in coated conductors for which the substrate and stabilizer are insulated from each other. The potential difference between the substrate and stabilizer, and the electric field in the substrate outside the normal zone can be accounted for by a large screening length in the substrate, comparable to the length of the sample. During a quench, the electric field inside the interface between YBCO and stabilizer, as well as in the buffer layer, can be several orders of magnitude greater than the longitudinal macroscopic electric field inside the normal zone. We speculate on the possibility of using possible microscopic electric discharges caused by this large ($\sim$kV/cm) electric field as a means to detect a quench.Comment: 8 pages, 4 figure

Charge reversal of colloidal particles

A theory is presented for the effective charge of colloidal particles in suspensions containing multivalent counterions. It is shown that if colloids are sufficiently strongly charged, the number of condensed multivalent counterion can exceed the bare colloidal charge leading to charge reversal. Charge renormalization in suspensions with multivalent counterions depends on a subtle interplay between the solvation energies of the multivalent counterions in the bulk and near the colloidal surface. We find that the effective charge is {\it not} a monotonically decreasing function of the multivalent salt concentration. Furthermore, contrary to the previous theories, it is found that except at very low concentrations, monovalent salt hinders the charge reversal. This conclusion is in agreement with the recent experiments and simulations

Theory of Diamagnetism in the Pseudogap Phase: Implications from the Self energy of Angle Resolved Photoemission

In this paper we apply the emerging- consensus understanding of the fermionic self energy deduced from angle resolved photoemisssion spectroscopy (ARPES) experiments to deduce the implications for orbital diamagnetism in the underdoped cuprates. Many theories using many different starting points have arrived at a broadened BCS-like form for the normal state self energy associated with a d-wave excitation gap, as is compatible with ARPES data. Establishing compatibility with the f-sum rules, we show how this self energy, along with the constraint that there is no Meissner effect in the normal phase are sufficient to deduce the orbital susceptibility. We conclude, moreover, that diamagnetism is large for a d-wave pseudogap. Our results should apply rather widely to many theories of the pseudogap, independent of the microscopic details.Comment: 15 pages, 8 figure

The effects of superconductor-stabilizer interfacial resistance on quench of current-carrying coated conductor

We present the results of numerical analysis of a model of normal zone propagation in coated conductors. The main emphasis is on the effects of increased contact resistance between the superconducting film and the stabilizer on the speed of normal zone propagation, the maximum temperature rise inside the normal zone, and the stability margins. We show that with increasing contact resistance the speed of normal zone propagation increases, the maximum temperature inside the normal zone decreases, and stability margins shrink. This may have an overall beneficial effect on quench protection quality of coated conductors. We also briefly discuss the propagation of solitons and development of the temperature modulation along the wire.Comment: To be published in Superconductor Science and Technology. This preprint contains one animated figure (Fig. 6(a)). when asked whether you want to play the content, click "Play". Acrobat Reader (Windows and Mac, but not Linux) will play embedded flash movies. In the printed copy Fig. 6(b) will show the temperature profile at gamma t=15