Current-ripple effect on superconductive dc critical current measurements

International Nuclear Information System (INIS)

Goodrich, L.F.; Bray, S.L.; Clark, A.F.

1988-01-01

The effect of sample-current power-supply ripple on dc critical current measurement in multifilamentary NbTi superconductors was evaluated. In general the ripple in a current supply became more significant above 500 A because effective filtering was hard to achieve. Ripple also caused noise at the input of the voltmeter used for the measurements. The quantitative effect of current ripple was studied using a battery current supply modified to allow the creation of ripple current with variable frequency and amplitude. Problems common to all large-conductor critical current measurements are discussed

Magnetic field dependence of the critical superconducting current induced by the proximity effect in silicon

International Nuclear Information System (INIS)

Nishino, T.; Kawabe, U.; Yamada, E.

1986-01-01

The magnetic field dependence of the critical superconducting current induced by the proximity effect in heavily-boron-doped Si is studied experimentally. It is found that the critical current flowing through the p-type-Si-coupled junction decreases with increasing applied magnetic field. The critical current can be expressed as the product of three factors: the current induced by de Gennes's proximity effect, the exponential decrease due to pair breaking by the magnetic field, and the usual diffraction-pattern-like dependence on the magnetic field due to the Josephson effect. The second factor depends on the carrier concentration in the semiconductor. The local critical current shows a rapid decrease at the edge of the electrodes

Toward superconducting critical current by design

OpenAIRE

Sadovskyy, I. A.; Jia, Y.; Leroux, M.; Kwon, J.; Hu, H.; Fang, L.; Chaparro, C.; Zhu, S.; Welp, U.; Zuo, J. -M.; Zhang, Y.; Nakasaki, R.; Selvamanickam, V.; Crabtree, G. W.; Koshelev, A. E.

2015-01-01

We present the new paradigm of critical current by design. Analogous to materials by design, it aims at predicting the optimal defect landscape in a superconductor for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To highlight this approach, we demonstrate the synergistic combination of critical current measurements on commercial high-temperature superconductors containing self-assembled and irradiation tailored correlated defects by using...

Toward Superconducting Critical Current by Design.

Science.gov (United States)

Sadovskyy, Ivan A; Jia, Ying; Leroux, Maxime; Kwon, Jihwan; Hu, Hefei; Fang, Lei; Chaparro, Carlos; Zhu, Shaofei; Welp, Ulrich; Zuo, Jian-Min; Zhang, Yifei; Nakasaki, Ryusuke; Selvamanickam, Venkat; Crabtree, George W; Koshelev, Alexei E; Glatz, Andreas; Kwok, Wai-Kwong

2016-06-01

A new critical-current-by-design paradigm is presented. It aims at predicting the optimal defect landscape in superconductors for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To this end, critical current measurements on commercial high-temperature superconductors are combined with large-scale time-dependent Ginzburg-Landau simulations of vortex dynamics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Differences between two definitions of the critical current of HTS coils

International Nuclear Information System (INIS)

Pitel, Jozef

2013-01-01

Definition of the critical current of a coil made of anisotropic high temperature superconducting conductor is rather complicated and ambiguous, since the magnetic field generated across the winding can differ considerably in relation to both its magnitude and orientation. Two definitions of the critical current of such coils are discussed. The first definition, very often used in calculations to analyze the current carrying capacity, electric field and power dissipation of individual turns, represents an operating current at which an electric field of 1 μV cm −1 appears on one turn. The second definition represents an integral approach, and is used in experiments. This definition introduces the critical current of the coil as an operating current at which an average electric field E s , usually 0.1 μV cm −1 , appears on coil terminals. As an example, the distribution of the critical current and electric field of individual turns in the winding of a BSCCO model coil was analyzed. Critical currents of the coil as a function of an external magnetic field parallel with the coil axis were calculated according to both definitions. The results show that the first definition, which characterizes the winding at the local level, is suitable for HTS coils either operating in self-field or in a low external field, because the differences between the critical currents and n-indices of individual turns are considerable. The second criterion is suitable for the HTS coils operating in high fields, i.e. like high field insert coils. The self-field of a high field insert coil is negligible if the external field is high. As a result, the critical currents of all turns are almost identical, and the anisotropy in I c (B) characteristic plays practically no role. Rather unexpected behavior of the voltage–current characteristic of the model coil is predicted if an external field is applied. (paper)

Characterization of the critical current and physical properties of superconducting epitaxial NbTiN sub-micron structures

Energy Technology Data Exchange (ETDEWEB)

Klimov, A., E-mail: aklimov@ite.waw.pl [Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw (Poland); Słysz, W.; Guziewicz, M. [Institute of Electron Technology, Al. Lotników 32/46, 02-668 Warsaw (Poland); Kolkovsky, V.; Zaytseva, I.; Malinowski, A. [Institute of Physics Polish Academy of Science, Al. Lotników 32/46, 02-668 Warsaw (Poland)

2017-05-15

Highlights: • This manuscript presents investigation of the critical current dependence of Nb(Ti)N nanostructured superconducting single photon detectors (SNSPD) in function of temperature and applied magnetic field. • Presented results are complimentary and compared with the same data received for submicron-wide single bridge Nb(Ti)N structures. • Our data demonstrate significant influence of local constrictions on physical properties of our SNSPD detectors. - Abstract: Measurements of critical current in NbTiN as a function of applied magnetic field and temperature are reported for two samples: 700-nm-wide bridge and 100-nm-wide meander. In 700-nm-wide NbTiN bridge we pinpointed the limiting factors for the critical current density to be current-driven vortex de-pinning at low temperatures and thermally activated flux flow closer to the transition temperature. In 100-nm-wide NbTiN meander we found phase slips activation, accompanied by hotspots formation at all measured temperatures. These two types of structures demonstrate different dependence of the critical current on the applied magnetic field. Although our NbTiN meander structures has high de-pairing critical current densities ∼10{sup 7} A/cm{sup 2} at low temperatures, the real critical currents are smaller due to the presence of the local constrictions.

Critical current of the nonuniform Josephson transition at intergranular boundary with random dislocation distribution

International Nuclear Information System (INIS)

Mejlikhov, E.Z.; Farzetdinova, R.M.

1997-01-01

Critical current of inhomogeneous intergranular Josephson transition is calculated in the assumption concerning superconductivity suppression by local strains of boundary dislocations with random distribution

Scanning Hall-probe microscopy system for two-dimensional imaging of critical current density in RE-123 coated conductors

International Nuclear Information System (INIS)

Higashikawa, K.; Inoue, M.; Kawaguchi, T.; Shiohara, K.; Imamura, K.; Kiss, T.; Iijima, Y.; Kakimoto, K.; Saitoh, T.; Izumi, T.

2011-01-01

Nondestructive characterization method of in-plane distribution of critical current density for coated conductors. Current distribution in a coated conductor compared with that from theoretical analysis. Relationship between local critical current density and local magnetic field. We have developed a characterization method for two-dimensional imaging of critical current density in coated conductors (CCs) based on scanning Hall-probe microscopy (SHPM). The distributions of the magnetic field around a sample were measured for several different conditions of external magnetic fields, and then were converted to those of the sheet current density which flowed to shield the external magnetic field or to trap the penetrated magnetic field. As a result, it was found that the amplitude of the sheet current density corresponded to that of critical current density almost in all the area of the sample except for the region where current direction changed. This indicates that we could obtain an in-plane distribution of the critical current density with a spatial resolution of around 100 μm in non-destructive manner by this method. We believe that this measurement will be a multifunctional and comprehensive characterization method for coated conductors.

Critical currents in columnar vanadium films

International Nuclear Information System (INIS)

Cherkasova, V.G.; Kolin'ko, A.E.; Slatin, A.E.; Fogel, N.Y.

1982-01-01

The angular dependence of the critical current I/sub c/ is studied in columnar vanadium films. In measurements in constant magnetic fields an anomalous maximum I/sub c/ is found on the I/sub c/(theta) curves at arbitrary values of the external magnetic field and temperature, when the magnetic field is perpendicular to the plane of the specimen. The angular dependence of I/sub c/ measured in constant reduced magnetic fields h = H/H/sub c/2(T,theta) shows no singularities in the vicinity of the angle at which the I/sub c/ peak is found in the case H = const, i.e., the critical current is isotropic. This implies that a change in the relative orientation of the vortices and column boundaries produces no change in critical current. The experimental data obtained permit the conclusion that the anisotropy of I/sub c/ observed in a constant magnetic field H is merely a consequence of the anisotropy of the critical magnetic field H/sub c/: the critical current ''tracking'' the magnitude and angular dependence of H/sub c/

Optimization of superconductor--normal-metal--superconductor Josephson junctions for high critical-current density

International Nuclear Information System (INIS)

Golub, A.; Horovitz, B.

1994-01-01

The application of superconducting Bi 2 Sr 2 CaCu 2 O 8 and YBa 2 Cu 3 O 7 wires or tapes to electronic devices requires the optimization of the transport properties in Ohmic contacts between the superconductor and the normal metal in the circuit. This paper presents results of tunneling theory in superconductor--normal-metal--superconductor (SNS) junctions, in both pure and dirty limits. We derive expressions for the critical-current density as a function of the normal-metal resistivity in the dirty limit or of the ratio of Fermi velocities and effective masses in the clean limit. In the latter case the critical current increases when the ratio γ of the Fermi velocity in the superconductor to that of the weak link becomes much less than 1 and it also has a local maximum if γ is close to 1. This local maximum is more pronounced if the ratio of effective masses is large. For temperatures well below the critical temperature of the superconductors the model with abrupt pair potential on the SN interfaces is considered and its applicability near the critical temperature is examined

Method for critical current testing

International Nuclear Information System (INIS)

Siddall, M.B.; Smathers, D.B.

1989-01-01

Superconducting critical current testing software was developed with four important features not feasible with analog test equipment. First, quasi-steady-state sample current conditions are achieved by incrementing sample current, followed by holding some milliseconds until the transient voltage decays before voltage sampling. Then the self-field correction from a helically wound sample is computed and subtracted from each sampled field reading. A copper wire inductively wound shunt which is used for quench protection has a constant measured resistance from which the shunt leakage current is computed and subtracted from the sample current by measuring the shunt voltage after each sample current reading. Finally, the critical current is recomputed from a least squares curve fit to the power law: E=A*In when the correlation coefficient for the fit is high enough to ensure a better result than the raw datum. Comparison with NBS Standard Reference Material (NbTi) and current round robin Nb/sub 3/Sn testing is examined

Effect of sheath material on critical current characteristics of MgB2 at high temperatures

International Nuclear Information System (INIS)

Kiuchi, M.; Yamauchi, K.; Kurokawa, T.; Otabe, E.S.; Matsushita, T.; Okada, M.; Tanaka, K.; Kumakura, H.; Kitaguchi, H.

2004-01-01

Critical current density and irreversibility field were measured at various temperatures and magnetic fields for MgB 2 PIT tape specimens with different sheaths materials. The experimental results were compared with theoretical estimations using the flux creep-flow model. It is found that the hardness of sheath material indirectly affects the pinning property only through the packing density of MgB 2 . It is considered that the critical current density is mainly determined by a low value of distributed local critical current density determined by grain connectivity. On the other hand, the irreversibility field which is approximately the same among the three tapes is mainly determined by the average pinning strength

Analysis of strain distribution and critical current of superconductors based on a strain-critical current measurement system

International Nuclear Information System (INIS)

Liu Fang; Wu Yu; Long Feng

2010-01-01

Based on Pacman device which is widely used to investigate the axial strain dependence of the critical current in superconductors, the finite element analysis method is employed to carry out the force analysis of the spring and the superconducting strand, thereby the axial and lateral strain distributions of the superconducting strand are obtained. According to the two extreme assumptions(low inter-filament resistance and high inter-filament resistance), the effects of the strain homogeneity at the cross section of the superconductor on the critical current is analyzed combined with the Nb 3 Sn deviatoric strain-critical current scaling law. (authors)

A critique of current developments in simultaneous localization and mapping

Directory of Open Access Journals (Sweden)

Shoudong Huang

2016-10-01

Full Text Available The number of research publications dealing with the simultaneous localization and mapping problem has grown significantly over the past 15 years. Many fundamental and practical aspects of simultaneous localization and mapping have been addressed, and some efficient algorithms and practical solutions have been demonstrated. The aim of this paper is to provide a critical review of current theoretical understanding of the fundamental properties of the SLAM problem, such as observability, convergence, achievable accuracy and consistency. Recent research outcomes associated with these topics are briefly discussed together with potential future research directions.

Upper critical fields and critical current densities of Fe-based superconductors as compared to those of other technical superconductors

Energy Technology Data Exchange (ETDEWEB)

Pallecchi, I., E-mail: ilaria.pallecchi@spin.cnr.it [CNR-SPIN, Corso Perrone 24, 16152 Genova (Italy); Tropeano, M. [Columbus Superconductors S.p.A, Via delle Terre Rosse 30, 16133 Genova (Italy); Lamura, G. [CNR-SPIN, Corso Perrone 24, 16152 Genova (Italy); Pani, M. [Dipartimento di Chimica e Chimica Industriale, Universita di Genova, Via Dodecaneso 31, 16146 Genova (Italy); Palombo, M. [Columbus Superconductors S.p.A, Via delle Terre Rosse 30, 16133 Genova (Italy); Dipartimento di Chimica e Chimica Industriale, Universita di Genova, Via Dodecaneso 31, 16146 Genova (Italy); Dipartimento di Fisica, Universita di Genova, Via Dodecaneso 33, 16146 Genova (Italy); Palenzona, A. [Dipartimento di Chimica e Chimica Industriale, Universita di Genova, Via Dodecaneso 31, 16146 Genova (Italy); Putti, M. [CNR-SPIN, Corso Perrone 24, 16152 Genova (Italy); Dipartimento di Fisica, Universita di Genova, Via Dodecaneso 33, 16146 Genova (Italy)

2012-11-20

Three years since the discovery by the Hosono's group of Fe-based superconductors, an enormous number of compounds, belonging to several different families have been discovered and fundamental properties have been deeply investigated in order to clarify the interplay between magnetisms and superconductivity in these compounds. Indeed, the actual potential of these compounds for practical applications remains still unclear. Fe-based superconductors are midway between high temperature superconductors (HTSCs) and MgB{sub 2}. In Fe-based superconductors the critical current is rather independent of the field, similarly to HTSCs, as a consequence of the exceptionally high upper critical field and strong pinning associated with nm-scale local modulations of the order parameter. They exhibit low anisotropy of the critical current with respect to the crystalline directions, as in the case of MgB{sub 2}, which allows current flow along the c-axis. However, Fe-based superconductor polycrystalline materials currently available still exhibit electromagnetic granularity, like the HTSCs, which suppresses superconducting current flow over long length. Whether the nature of such granularity is extrinsic, as due to spurious phases or cracks between grains or intrinsic, as related to misalignment of adjacent grains, is under debate. These aspects will be reviewed in the light of the recent literature.

Method for measuring the resistive transition and critical current in superconductors using pulsed current

International Nuclear Information System (INIS)

McGinnis, W.C.; Jones, T.E.

1993-01-01

A method is described for measuring the intragranular critical current of a granular superconductive material, comprising the steps of: conducting a substantially rectangular electronic pulse through said material so as to conduct a current through said material such that when said intragranular critical current of said material is exceeded, any grains present in said material are in a superconducting state when said current is less than said intragranular critical current, said material having a critical temperature; measuring said current through said material while conducting said pulse; measuring a voltage difference across said material while conducting said pulse; and determining said intragranular critical current through said material by varying said current to discern a current level at which an electrical resistance of said material increases to that of a non-superconducting state as the grains of said material transition from said superconducting to said non-superconducting state

Off-critical local height probabilities on a plane and critical partition functions on a cylinder

Directory of Open Access Journals (Sweden)

Omar Foda

2018-03-01

Full Text Available We compute off-critical local height probabilities in regime-III restricted solid-on-solid models in a 4N-quadrant spiral geometry, with periodic boundary conditions in the angular direction, and fixed boundary conditions in the radial direction, as a function of N, the winding number of the spiral, and τ, the departure from criticality of the model, and observe that the result depends only on the product Nτ. In the limit N→1, τ→τ0, such that τ0 is finite, we recover the off-critical local height probability on a plane, τ0-away from criticality. In the limit N→∞, τ→0, such that Nτ=τ0 is finite, and following a conformal transformation, we obtain a critical partition function on a cylinder of aspect-ratio τ0. We conclude that the off-critical local height probability on a plane, τ0-away from criticality, is equal to a critical partition function on a cylinder of aspect-ratio τ0, in agreement with a result of Saleur and Bauer.

Critical carbon input to maintain current soil organic carbon stocks in global wheat systems.

Science.gov (United States)

Wang, Guocheng; Luo, Zhongkui; Han, Pengfei; Chen, Huansheng; Xu, Jingjing

2016-01-13

Soil organic carbon (SOC) dynamics in croplands is a crucial component of global carbon (C) cycle. Depending on local environmental conditions and management practices, typical C input is generally required to reduce or reverse C loss in agricultural soils. No studies have quantified the critical C input for maintaining SOC at global scale with high resolution. Such information will provide a baseline map for assessing soil C dynamics under potential changes in management practices and climate, and thus enable development of management strategies to reduce C footprint from farm to regional scales. We used the soil C model RothC to simulate the critical C input rates needed to maintain existing soil C level at 0.1° × 0.1° resolution in global wheat systems. On average, the critical C input was estimated to be 2.0 Mg C ha(-1) yr(-1), with large spatial variability depending on local soil and climatic conditions. Higher C inputs are required in wheat system of central United States and western Europe, mainly due to the higher current soil C stocks present in these regions. The critical C input could be effectively estimated using a summary model driven by current SOC level, mean annual temperature, precipitation, and soil clay content.

Critical temperature gradient and critical current density in thin films of a type I superconductor

Energy Technology Data Exchange (ETDEWEB)

Heubener, R P

1968-12-16

Measurements of the critical temperature gradient and the critical current density in superconducting lead films in a transverse magnetic field indicate that the critical current flows predominantly along the surface of the films and that the critical surface currents contribute only very little to the Lorentz force on a fluxoid.

Enhancing critical current density of cuprate superconductors

Science.gov (United States)

Chaudhari, Praveen

2015-06-16

The present invention concerns the enhancement of critical current densities in cuprate superconductors. Such enhancement of critical current densities include using wave function symmetry and restricting movement of Abrikosov (A) vortices, Josephson (J) vortices, or Abrikosov-Josephson (A-J) vortices by using the half integer vortices associated with d-wave symmetry present in the grain boundary.

Critical currents in multilayered superconducting films

International Nuclear Information System (INIS)

Raffy, Helene

1977-01-01

The superconducting critical currents Isub(c) were measured as a function of magnetic field H and temperature T, on multilayered films. These films consist of alternating layers of two different superconductors S 1 and S 2 being a weaker superconductor acting as a flux pinning barrier region. A strong anisotropy was observed between the two situations where the magnetic field H is applied parallel or perpendicular to the layers. In the case discussed, there is a peak effect in the curves Isub(c)H well defined at the highest temperatures, and disappearing at low temperatures. The anisotropy of the critical current at constant field presents a maximum at a temperature T* close to the critical temperature Tsub(c 2 ) of S 2 [fr

Simulation of transport critical current of Bi2223/Ag tape with ferromagnetic shielding

International Nuclear Information System (INIS)

Gu, C.; Alamgir, A.K.M.; Qu, T.M.; Han, Z.

2008-01-01

Ferromagnetic shielding (FS) was coated onto the surface of the Bi2223/Ag multi-filamentary tape. Transport critical current of the Bi2223/Ag multi-filamentary tape with a FS was systematically studied by numerical simulation. In the help of a finite element analysis (FEA) tool, we are able to understand how the FS alters the flux inside the superconductor region and thus increases and decreases the critical current density locally. The results show the open FS function both positively and negatively to the performance of the tape. An optimization process was proposed, aiming to reach a tradeoff between I c increasing and less usage of the ferromagnetic material. Three important shielding parameters, shielding width, shielding thickness, and shielding material were taken into account

Simulation of transport critical current of Bi2223/Ag tape with ferromagnetic shielding

Energy Technology Data Exchange (ETDEWEB)

Gu, C. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China)], E-mail: guchen@tsinghua.edu.cn; Alamgir, A.K.M. [Faculty of Engineering, Yokohama National University, 75-9 Tokiwadai, Hodogaya, ku, Yokohama (Japan); Qu, T.M. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China); Key Laboratory for Advanced Materials Processing Technology, Ministry of Education (China); Han, Z. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China)

2008-09-15

Ferromagnetic shielding (FS) was coated onto the surface of the Bi2223/Ag multi-filamentary tape. Transport critical current of the Bi2223/Ag multi-filamentary tape with a FS was systematically studied by numerical simulation. In the help of a finite element analysis (FEA) tool, we are able to understand how the FS alters the flux inside the superconductor region and thus increases and decreases the critical current density locally. The results show the open FS function both positively and negatively to the performance of the tape. An optimization process was proposed, aiming to reach a tradeoff between I{sub c} increasing and less usage of the ferromagnetic material. Three important shielding parameters, shielding width, shielding thickness, and shielding material were taken into account.

High Critical Current Coated Conductors

Energy Technology Data Exchange (ETDEWEB)

Paranthaman, M. P.; Selvamanickam, V. (SuperPower, Inc.)

2011-12-27

One of the important critical needs that came out of the DOE’s coated conductor workshop was to develop a high throughput and economic deposition process for YBCO. Metal-organic chemical vapor deposition (MOCVD) technique, the most critical steps in high technical micro fabrications, has been widely employed in semiconductor industry for various thin film growth. SuperPower has demonstrated that (Y,Gd)BCO films can be deposited rapid with world record performance. In addition to high critical current density with increased film thickness, flux pinning properties of REBCO films needs to be improved to meet the DOE requirements for various electric-power equipments. We have shown that doping with Zr can result in BZO nanocolumns, but at substantially reduced deposition rate. The primary purpose of this subtask is to develop high current density MOCVD-REBCO coated conductors based on the ion-beam assisted (IBAD)-MgO deposition process. Another purpose of this subtask is to investigate HTS conductor design optimization (maximize Je) with emphasis on stability and protection issues, and ac loss for REBCO coated conductors.

Critical transport current in granular high temperature superconductors

International Nuclear Information System (INIS)

Bogolyubov, N.A.

1999-01-01

The temperature and size dependence of the critical current in a zero magnetic field of three bismuth-based ceramic samples with round cross section and one sample with rectangular triangle cross section have been studied by a contactless technique. It is shown that the critical current can be presented as a product of the temperature and size dependent factors. The temperature-dependent multiplier reflects the individual peculiarities of the Josephson net of each sample, while the size factor is a homogeneous function of the cross-section sizes. The index of this function is independent of the cross-section form, the temperature and individual properties of HTSC samples. The radial distribution of critical current density in round samples and dependence of the critical current density on the magnetic conduction in granular HTSC have been found from the analysis of experimental data

Critical current enhancement in high Tc superconductors

International Nuclear Information System (INIS)

Jin, S.; Graebner, J.E.; Tiefel, T.H.

1990-01-01

Progress toward major technological applications of the bulk, high T c superconductors has been hindered by two major barriers, i.e., the Josephson weak-links at grain boundaries and the lack of sufficient intragrain flux pinning. It has been demonstrated that the weak link problem can be overcome by extreme alignment of grains such as in melt-textured-growth (MTG) materials. Modified or improved processing by various laboratories has produced further increased critical currents. However, the insufficient flux pinning seems to limit the critical current density in high fields to about 10 4 --10 5 A/cm 2 at 77K, which is not satisfactory for many applications. In this paper, processing, microstructure, and critical current behavior of the MTG type superconductors are described, and various processing possibilities for flux pinning enhancement are discussed

Critical-state model for the determination of critical currents in disk-shaped superconductors

International Nuclear Information System (INIS)

Frankel, D.J.

1979-01-01

A series of experiments has been carried out on the flux trapping and shielding capabilities of a flat strip of Nb-Ti/Cu composite material. A circular piece of material from the strip was tested in a uniform field directed perpendicularly to the surface of the sample. Profiles of the normal component of the field along the sample diameter were measured. The critical-state model was adapted for this geometry and proved capable of reproducing the measured field profiles. Model curves agreed well with experimental field profiles generated when the full sample was in the critical state, when only a portion of the sample was in the critical state, and when profiles were obtained after the direction of the rate change of the magnetic field was reversed. The adaption of the critical-state model to disk geometry provides a possible method either to derive values of the critical current from measurements of field profiles above thin flat samples, or to predict the trapping and shielding behavior of such samples if the critical current is already known. This method of determining critical currents does not require that samples be formed into narrow strips or wires, as is required for direct measurements of J/sub c/, or into tubes or cylinders, as is usually required for magnetization-type measurements. Only a relatively small approximately circular piece of material is needed. The method relies on induced currents, so there is no need to pass large currents into the sample. The field-profile measurements are easily performed with expensive Hall probes and do not require detection of the resistive transition of the superconductor

Model for the resistive critical current transition in composite superconductors

International Nuclear Information System (INIS)

Warnes, W.H.

1988-01-01

Much of the research investigating technological type-II superconducting composites relies on the measurement of the resistive critical current transition. We have developed a model for the resistive transition which improves on older models by allowing for the very different nature of monofilamentary and multifilamentary composite structures. The monofilamentary model allows for axial current flow around critical current weak links in the superconducting filament. The multifilamentary model incorporates an additional radial current transfer between neighboring filaments. The development of both models is presented. It is shown that the models are useful for extracting more information from the experimental data than was formerly possible. Specific information obtainable from the experimental voltage-current characteristic includes the distribution of critical currents in the composite, the average critical current of the distribution, the range of critical currents in the composite, the field and temperature dependence of the distribution, and the fraction of the composite dissipating energy in flux flow at any current. This additional information about the distribution of critical currents may be helpful in leading toward a better understanding of flux pinning in technological superconductors. Comparison of the models with several experiments is given and shown to be in reasonable agreement. Implications of the models for the measurement of critical currents in technological composites is presented and discussed with reference to basic flux pinning studies in such composites

The critical current of superconductors: an historical review

International Nuclear Information System (INIS)

Dew-Hughes, D.

2001-01-01

The most important practical characteristic of a superconductor is its critical current density. This article traces the history, both of the experimental discoveries and of the development of the theoretical ideas that have lead to the understanding of those factors that control critical current densities. These include Silsbee's hypothesis, the Meissner effect, London, Ginsburg-Landau and Abrikosov theories, flux pinning and the critical state, and the control of texture in high temperature superconductors

Correlation of superconductor strand, cable, and dipole critical currents in CBA magnets

International Nuclear Information System (INIS)

Tannenbaum, M.J.; Garber, M.; Sampson, W.B.

1982-01-01

A calibration between vendor critical current data for 0.0268'' diameter superconductor strand supplied to Fermilab, and the BNL 10 -12 Ωcm critical current specification is presented. Vendor critical current data for over 400 Fermilab type billets are shown, both as supplied by the vendor and converted to BNL units. Predictions of cable critical current are made using the sum of the critical currents of the 23 strands, where all strands from the same half billet are assigned the same critical current. The measured critical current shows excellent correlation to the predicted value and is approximately 14 +- 2 percent below it. Colliding Beam Accelerator (CBA) full length dipoles reach the conductor critical current limit, essentially without training. Magnet performance is predictable from the measured critical current of a short sample of cable to within 2%

Critical current studies of a HTS rectangular coil

Energy Technology Data Exchange (ETDEWEB)

Zhong, Z. [Department of Engineering, University of Cambridge (United Kingdom); Chudy, M., E-mail: Michal.chudy@stuba.sk [Graduate School of Technology Management, University of Pretoria (South Africa); Institute of Power and Applied Electrical Engineering, Slovak University of Technology in Bratislava (Slovakia); Ruiz, H.S. [Department of Engineering, University of Leicester, Leicester LE1 7RH (United Kingdom); Zhang, X.; Coombs, T. [Department of Engineering, University of Cambridge (United Kingdom)

2017-05-15

Highlights: • Unique square pancake coil was manufactured. • Measurements in relatively high magnetic field were performed. • Different sections of the coil were characterized. • Parts of the coil which are limiting critical current were identified. - Abstract: Nowadays, superconducting high field magnets are used in numerous applications due to their superior properties. High temperature superconductors (HTS) are usually used for production of circular pancake or racetrack coils. However different geometries of HTS coils might be required for some specific applications. In this study, the HTS coil wound on a rectangular frame was fully characterized in homogeneous DC background field. The study contains measurements of critical current angular dependencies. The critical current of the entire coil and two selected strands under different magnitudes and orientations of external magnetic fields are measured. The critical regions of the coil in different angular regimes are determined. This study brings better understanding of the in- field performance of HTS coils wound on frames with right-angles.

Microstructures and critical currents in high-Tc superconductors

International Nuclear Information System (INIS)

Suenaga, Masaki

1998-01-01

Microstructural defects are the primary determining factors for the values of critical-current densities in a high T c superconductor after the electronic anisotropy along the a-b plane and the c-direction. A review is made to assess firstly what would be the maximum achievable critical-current density in YBa 2 Cu 3 O 7 if nearly ideal pinning sites were introduced and secondly what types of pinning defects are currently introduced or exist in YBa 2 Cu 3 O 7 and how effective are these in pinning vortices

Critical current density and upper critical field of the PbMo6S8 Chevrel phase

International Nuclear Information System (INIS)

Seeber, B.; Decroux, M.; Fischer, O.

1988-01-01

A detailed discussion of critical current density and upper critical field for PbMo 6 S 8 (PMS) is given. It is shown that PMS bulk as well as wire samples can be prepared with sufficient quality to observe the scaling law for the volume pinning force. Using the scaling law an estimation for the critical current density as a function of field and temperature was made. The study also indicates that a substantial improvement of the critical current density can be expected by optimizing the upper critical field without changing the microstructure. It is shown that the availability of high quality samples of EuMo 6 S 8 , to which PMS is similar, makes it possible to study separately the different physical parameters which determine the upper critical field in PMS

Simulation of the d.c. critical current in superconducting sintered ceramics

International Nuclear Information System (INIS)

Riedinger, R.; Habig, P.; Hlil, E.K.; Arnaud, M.; Boulesteix, C.

1990-01-01

The new superconducting high-T c sintered ceramics can be described in some case as a lattice of interconnected rods, in other cases as a more or less random packing of parallelepiped crystallites; their size is about a few microns. The d.c. critical current at zero voltage of such a material is not related to the critical current of the bulk material, but to its granular structure. Indeed, the critical current between two adjacent cells is governed by the critical current of the weak link between them; this link behaves within some limits as a Josephson junction, the critical current of which is known. For our present problem, the system can be modeled as a lattice of Josephson junctions. We present here results for the d.c. critical current at zero voltage of lattices of identical Josephson junctions in two dimensions. The influence of the finiteness of size of the sample is examined. The relationship with normal conductivity simulations and percolation is discussed

Field modulation of the critical current in magnetic Josephson junctions

International Nuclear Information System (INIS)

Blamire, M G; Smiet, C B; Banerjee, N; Robinson, J W A

2013-01-01

The dependence of the critical current of a simple Josephson junction on the applied magnetic field is well known and, for a rectangular junction, gives rise to the classic ‘Fraunhofer’ modulation with periodic zeros at the fields that introduce a flux quantum into the junction region. Much recent work has been performed on Josephson junctions that contain magnetic layers. The magnetization of such layers introduces additional flux into the junction and, for large junction areas or strong magnetic materials, can significantly distort the modulation of the critical current and strongly suppress the maximum critical current. The growing interest in junctions that induce odd-frequency triplet pairing in a ferromagnet, and the need to make quantitative comparisons with theory, mean that a full understanding of the role of magnetic barriers in controlling the critical current is necessary. This paper analyses the effect of magnetism and various magnetic configurations on Josephson critical currents; the overall treatment applies to junctions of general shape, but the specific cases of square and rectangular junctions are considered. (paper)

Critical current, pinning and resistive state of superconducting single-crystal niobium with different types of defect structure

International Nuclear Information System (INIS)

Sokolenko, V.I.; Starodubov, Ya.D.

2005-01-01

Critical current pinning and resistive state of single crystal niobium of texture orientation are studied for different structural states obtained by rolling at 20 K by 42% and polishing the surface layers. It is found that the heterogeneous structures typical of the strained sample even after its thinning down to approx 10% display a lower current-carrying capability due to an increase of the thermomagnetic instability within the fragmented structure sections in the near-surface layers. For a homogeneous defect structure of the sample core with the density of equilibrium distributed dislocations of 1.3 centre dot 10 11 cm -2 , a correlation between the normal current density and the critical current density in the resistive state is found, in agreement with the concepts of flux creep due to the scatter of local values of J c

Critical power for lower hybrid current drive

International Nuclear Information System (INIS)

Assis, A.S. de; Sakanaka, P.H.; Azevedo, C.A. de; Busnardo-Neto, J.

1995-11-01

We have solved numerically the quasilinear Fokker-Planck equation which models the critical power for lower hybrid wave current drive. An exact value for the critical power necessary for current saturation, for tokamak current drive experiments, has been obtained. The nonlinear treatment presented here leads to a final profile for the parallel distribution function which is a plateau only in a part of the resonance region. This form of the distribution function is intermediate between two well known results: a plateau throughout the resonance region for the linear strong-source regime, D wave >> D coll and no plateau at all in the resonance region the linear weak-source regimen, D wave coll . The strength of the external power source and the value of the dc electric field are treated as given parameters in the integration scheme. (author). 24 refs, 6 figs

A statistical study of current-sheet formation above solar active regions based on selforganized criticality

Science.gov (United States)

Dimitropoulou, M.; Isliker, H.; Vlahos, L.; Georgoulis, M.; Anastasiadis, A.; Toutountzi, A.

2013-09-01

We treat flaring solar active regions as physical systems having reached the self-organized critical state. Their evolving magnetic configurations in the low corona may satisfy an instability criterion, related to the excession of a specific threshold in the curl of the magnetic field. This imposed instability criterion implies an almost zero resistivity everywhere in the solar corona, except in regions where magnetic-field discontinuities and. hence, local currents, reach the critical value. In these areas, current-driven instabilities enhance the resistivity by many orders of magnitude forming structures which efficiently accelerate charged particles. Simulating the formation of such structures (thought of as current sheets) via a refined SOC cellular-automaton model provides interesting information regarding their statistical properties. It is shown that the current density in such unstable regions follows power-law scaling. Furthermore, the size distribution of the produced current sheets is best fitted by power laws, whereas their formation probability is investigated against the photospheric magnetic configuration (e.g. Polarity Inversion Lines, Plage). The average fractal dimension of the produced current sheets is deduced depending on the selected critical threshold. The above-mentioned statistical description of intermittent electric field structures can be used by collisional relativistic test particle simulations, aiming to interpret particle acceleration in flaring active regions and in strongly turbulent media in astrophysical plasmas. The above work is supported by the Hellenic National Space Weather Research Network (HNSWRN) via the THALIS Programme.

Influence of self-field on the critical current of Bi-2223/Ag tapes

International Nuclear Information System (INIS)

Lehtonen, Jorma; Korpela, Aki; Nah, Wansoo; Kang, Joonsun; Kovac, Pavol; Melisek, Tibor

2004-01-01

The knowledge of critical current density in a superconducting wire is essential in order to compute AC losses. In HTS tapes the critical current density is difficult to estimate from the measured critical current because self-field tends to reduce the current carrying capacity. In this paper the critical current is measured with a single sample and with two similar samples connected in antiparallel in order to compensate the self-field. Both types of measurement are simulated with finite element method. The simulations help to understand the relation between the measured critical current and material properties. The results suggest that in a high quality tape the self-field effect reduced the measured critical current ∼25% if compared to the real critical current at the zero external field

Local eddy current measurements in pulsed fields

Energy Technology Data Exchange (ETDEWEB)

Espina-Hernandez, J.H. [SEPI-Electronica, ESIME-IPN, UPALM Edif. ' Z' . Zacatenco, Mexico DF 07738 (Mexico)], E-mail: jhespina@gmail.com; Groessinger, R. [Institute of Solid State Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, A-1040 Vienna (Austria); Hallen, J.M. [Departamento de Ingenieria Metalurgica, IPN-ESIQIE, UPALM Edif. 7, Zacatenco, Mexico DF 07738 (Mexico)

2008-07-15

This work presents new eddy current measurements in pulsed fields. A commercial point pick-up coil is used to detect the induction signal along the radius of Cu and Al samples with cylindrical shape and diameters between 5 and 35 mm. Local eddy current measurements were performed on the surface of conducting materials due to the small dimensions of the coil. A simple electrical circuit, used as a model, is proposed to describe the local eddy current effect in pulsed fields. The proposed model allows to calculate the phase shift angle between the signal proportional to eddy currents and the applied external field in a pulsed field magnetometer.

Critical current of high Tc superconducting Bi223/Ag tapes

NARCIS (Netherlands)

Huang, Y.; ten Haken, Bernard; ten Kate, Herman H.J.

1998-01-01

The magnetic field dependence of the critical current of various high Tc superconducting Bi2223/Ag tapes indicates that the transport current is carried through two paths: one is through weakly-linked grain boundaries (Josephson junctions); another is through well-connected grains. The critical

The critical current of granular superconductor

International Nuclear Information System (INIS)

Ignat'ev, V.K.

1998-01-01

A mechanism of hyper vortex pinning in granular superconductors is proposed to describe the field dependence of the critical current density and pinning potential. The results are in a good agreement with the experiment. The model represents the peak effect and the percolation mechanism of conductivity in ceramic superconductors

Effect of strain on the critical-current density of Cu-Nb composites

International Nuclear Information System (INIS)

Klein, J.D.; Rose, R.M.

1987-01-01

Microfilamentary superconducting composites of Nb fibers in Cu matrices prepared by the stack and draw method were tested for tensile critical-current performance at 4.2 K. The superconducting critical-current densities increased exponentially under the influence of an applied mechanical strain until the onset of Nb fiber plastic deformation. In the elastic range, the critical-current densities conformed to log 10 J/sub c/ = m (strain)+b. In several tests the critical current was increased by more than an order of magnitude by the applied strain. This behavior is consistent with an increase in the upper critical field of the Nb fibers by the applied stress

Effects of small magnetic fields on the critical current of thin films

International Nuclear Information System (INIS)

Passos, Wagner de Assis Cangussu; Lisboa-Filho, Paulo Noronha; Ortiz, Wilson Aires; Kang, W.N.; Choi, Eun-Mi; Hyeong-Jin, Kim; Lee, Sung-Ik Lee

2002-01-01

Full text: Magnetic fields applied perpendicularly to superconducting thin films may produce dendritic patterns, where penetrated and Meissner regions coexist, as observed in Nb, YBaCuO and MgB 2 [1]. A temperature-dependent limiting-field, Hd(T), separates the dendritic mode from a critical-state-like penetration regime. Due to large demagnetizing factors in the perpendicular geometry, small fields may be enough to drive portions of the sample into the mixed state. Lack of symmetry and local defects might then permeate the dendritic mode. Hd(T) is related[2] to the bulk lower critical field, Hc1, which depends on the in-plane current density, J. Not surprisingly, Hd is depressed by J[3]. The dendritic mode can be detected by the AC-susceptibility: penetrated fingers act as intergranular material, and the imaginary component peaks at Tc-inter(J). Films of 0.2-0.4 microns, with millimeter lateral sizes, develop dendrites when submitted to Earth's field[2], what limits the critical current, J c . This contribution studies how J c is affected by field-induced granularity in thin films. 1. C. A. Duran et al., PRB 52 (1995) 75; P. Leiderer et al., PRL. 71 (1993) 2646; T.H. Johansen et al., Supercond. Sci. Technol. 14 (2001) 1. 2. W. A. Ortiz et al., Physica C 361 (2001) 267. 3. A. V. Bobyl et al., cond-mat/0201260, submitted to APL

Critical current of pure SNS junctions

International Nuclear Information System (INIS)

Golub, A.A.; Bezzub, O.P.

1982-01-01

Boundary conditions at the superconductor-normal metal interface are determined, taking into account the differences in the effective masses and the density of states of the metals constituting the transition and assumed to be pure. The potential barrier of the interface is chosen to be zero. The critical current of the junction is calculated [ru

Current algebra and the local nature of symmetries in local quantum theory

International Nuclear Information System (INIS)

Doplicher, S.

In this report we mainly discuss the problem of finding local observables which measure the charges in a volume smaller than their localization region, in particular providing the existence of local observables with a specific physical interpretation. In the same way we can also establish the existence of a version of the current algebra structure. Similar local observables can be constructed for the energy-momentum; we also comment on the local implementation of supersymmetries. (orig./HSI)

Strain reduced critical current in Bi-2223/Ag superconductors under axial tension and compression

International Nuclear Information System (INIS)

Haken, B. ten; Godeke, A.; Kate, H.H.J. ten

1997-01-01

The critical current of Ag sheathed Bi(Pb)SrCaCuO-2223 tape conductors is investigated as a function of various strain components. A reduction of the critical current occurs due to both tensile or a compressive strain. The critical current reduction is qualitatively similar with the results as observed in Bi-2212 conductors. An axial compression leads to an immediate critical current reduction. The critical current in an axially elongated sample remains nearly constant up to a certain limit typically close to 0.3% strain. For a larger elongation the critical current reduces rapidly. A transverse pressure acting on the tape surface leads also to an irreversible critical current reduction. This behavior is compared with the influence of an axial compression with an effective Young's modulus. The deformation induced critical current reductions in Bi-2223 conductors can be described by a model that is already proposed for Bi-2212 conductors. This model is based on the irreversible nature of the critical current reduction due to a certain deformation

Strain dependence of the critical current and critical field in multifilamentary Nb3Sn composites

International Nuclear Information System (INIS)

Ekin, J.W.

1979-01-01

High-J/sub c/ multifilamentary Nb 3 Sn superconductors with widely varying amounts of prestrain and critical field values can be characterized fairly accurately by a single normalized critical field-strain relationship. Such a relationship permits first order prediction of critical-current degradation at arbitrary magnetic field magnitudes with knowledge of only two parameters for any conductor, the prestrain and the maximum critical field. Some of the conductor-fabrication factors affecting the parameters are considered

Critical current properties in superconducting melt processed Y-Ba-Cu-O

International Nuclear Information System (INIS)

Matsushita, Teruo

1993-01-01

The critical current density in bulk superconducting Y-Ba-Cu-O has been remarkably improved by employing the so-called melt process. However, its value is still far below those reported in single-crystalline thin films. Important key factors that determine the critical current density are the flux pinning mechanism and defective structures such as cracks or weak links. In this article, these factors in melt-processed Y-Ba-Cu-O are argued from various measurements of the critical current density on the microstructure dependence, the magnetic field dependence, the temperature dependence, the history effect, the longitudinal field effect and the imaginary ac susceptibility. As for the pinning mechanism, it is concluded that the dominant pinning centers in the high temperature region around 77 K are normal 211 (Y 2 BaCuO 5 ) particles, while small defects such as lattice defects or oxygen deficiencies seem to be dominant in the lower temperature region. It is suggested that much finer normal particles should be introduced in order to improve the critical current density especially at higher temperatures. From the rapid decrease of the critical current density with elevating temperature below 30 K, some kind of weak links are considered to still remain in these materials. However, the observed critical current density did not depend on the history of application of the magnetic field and a large enhancement of the critical current density was observed in the longitudinal field geometry at 4.2 K. These results suggest that the weak links in these materials are of much different kind from those at large angle grain boundaries in sintered polycrystalline materials. From the X-ray diffraction measurements, a domain structure of a mean domain size of about 100 μm was found. These domain boundaries may cause weak links in melt-processed Y-Ba-Cu-O. It is also shown that the typical size of channels of flowing current can be obtained by the imaginary ac susceptibility

Stress induced degradation of critical currents in filamentary Nb3Sn

International Nuclear Information System (INIS)

McDougall, I.L.

1976-01-01

An investigation of the critical stress and strain values of bronze, Nb 3 Sn composites at 4.2 K has been made with simultaneous determination of critical currents in a field of 2.5 Tesla. Evidence of grain boundary microcrack formation has been found associated with reversible degradation of critical current. At a critical strain characteristic of the composite geometry these cracks propagate to give a GB fracture network. A compound with a small grain size formed at low temperatures has the best mechanical properties with a critical strain to the onset of reversible degradation of about 0.5%. (author)

Microstructural factors influencing critical-current densities of high-temperature superconductors

International Nuclear Information System (INIS)

Suenaga, M.

1992-01-01

Microstructural defects are the primary determining factors for the values of critical current densities in superconductors. A review is made to assess, (1) what would be the maximum achievable critical-current density in the oxide superconductors if nearly ideal pinning sites were introduced? and (2) what types of pinning defects are currently introduced in these superconductors and how effective are these in pinning the vortices? Only the case where the applied field is parallel to the c-axis is considered here

Critical unpairing currents in narrow niobium films

International Nuclear Information System (INIS)

Gershenzon, M.E.; Gubankov, V.N.

1979-01-01

Investigated are the dependences of critical currents of narrow ( with the width of W=0.5-15 μm) superconducting niobium films on temperature and a magnetic field. The proposed method of film production with the width of the 1μm order and with small edge inhomogeneities ((<=500 A) permitted to realize the Ginsburg-Landau unpairing currents in the wide range of temperatures. The correct comparison with the theory showed that the unpairing currents are observed if W(< or approximately) 2delta, where delta is the effective depth of the penetration of the perpendicular magnetic field

Critical currents and fields of disordered nanocrystalline superconductors

International Nuclear Information System (INIS)

Yavary, H.; Shahzamanian, M.A.; Rabbani, H.

2007-01-01

Full text: There is an enormous effort directed at increasing the upper critical field of the superconducting materials because this upper critical field provides a fundamental limit to the maximum field a magnet system can produce. High-energy particle accelerators and medical resonance imaging body scanners are limited by the for NbTi (10 T). Gigahertz class nuclear-magnetic-resonance and high field laboratory magnets are limited by for Nb 3 Sn (23 T) [1]. However, the values of critical current density are too low for industrial use, possibly because of degraded or nonsuperconducting phases, such as MoS 2 or Mo 2 S 3 , at the grain boundaries or because the pinning site density is not high enough. It has long been known that decreasing the grain size of low-temperature superconducting (LTS) materials, such as Nb 3 Sn, increases the density of flux pinning sites and hence. Nanocrystalline materials are characterized by ultrafine grains and a high density of grain boundaries [2]. Hence nanocrystalline materials can exhibit unusual physical, chemical, and mechanical properties with respect to conventional polycrystalline materials. The purpose of this paper is to investigate the structure of currents and fields in disordered nanocrystalline superconducting materials by the use of quasiclassical many body techniques. The Keldish Greens functions are used to calculate the current density of the system. Since the disorder and microstructure of these nanocrystalline materials are on a sufficiently short length scale as to increase both the density of pinning site and the upper critical field. (authors)

Critical potentials, leptons, and weak currents

International Nuclear Information System (INIS)

Smith, P.F.; Lewin, J.D.

1977-12-01

A theoretical study is made of the interaction of very strong localised electromagnetic potentials with charged leptons, and with the vacuum state. The principal objective is to investigate the phenomena which occur when the potential reaches or exceeds the critical value at which bound levels are drawn into the lower continuum. The behaviour of bound and continuum solutions of the Dirac equation for the specific model of a short range potential well in an arbitrarily large bounded volume is examined in detail. Vacuum polarisation effects are computed by summation over the infinite set of single particle levels, and special attention is given to the behaviour of the overall charge distribution as the potential strength increases through the critical value. The most significant features of the results are (a) the formation of highly localised electron or muon bound states, (b) similar critical potential strengths for electrons and muons, and (c) redefinition of the vacuum by one charge unit at the critical potential. These features are analogous to some properties of leptonic and hadronic weak currents, and the hypothesis is proposed that strong short range potentials may provide a possible mediating mechanism for the weak interaction and also a lepton confinement mechanism within the structure of hadrons. (author)

On the critical current of ionisation waves in gas discharges

International Nuclear Information System (INIS)

Sato, M.

1982-01-01

Measurement methods for determining the critical current of ionisation waves in gas discharge tubes are examined in detail. The conventional visual method which finds the current at which the waves disappear is erroneous since the criterion, 'observable', depends on the observing conditions. In the rigorous method it is defined as a current at which the linear growth rate of waves is zero. For the measured upper critical (Pupp) current of argon gas, close agreement is found between the results of other workers and those of the present author over a wide range of pressure-radius product 0.3 approximately equal to 60 Torr cm. (author)

Microstructure and critical current density in high-Tc metal oxide superconductors

International Nuclear Information System (INIS)

Johnson, S.M.; Gusman, M.I.

1992-03-01

Superconductor powders in the U-Ba-Cu-O (YBCO) and Bi-Pb-Sr-Ca-Cu-O (BSCCO) systems were synthesized by freeze-drying. Powders were characterized, and processed into samples for evaluation of superconducting behavior. Freeze-drying is attractive because the powders have high purity, are homogeneous, have a small size and are active. YBCO powders can be sintered to high density at 890 degrees C. Many compositions, processing approaches and heat treatments were explored in an effort to understand relations between microstructure and critical density, and to improve the critical current density. Powders were also formed into sputtering targets for coating preparation at Stanford University. The highest critical current density achieved with the YBCO powders was ∼15,000 A/cm 2 at 4.2K and 0.5T using powders treated to prevent carbon contamination. The BSCCO materials with the highest critical current density, ∼30,000 A/cm 2 at the same conditions were formed by heat treating melted and quenched samples. All critical current density measurements were made by Stanford University, a subcontractor to this effort. Stanford University also prepared coatings by off-axis magnetron sputtering

Determination of the inter- and intra-granular critical currents in superconducting YBa2Cu3O7 welds

International Nuclear Information System (INIS)

Bozzo, B; Iliescu, S; Bartolome, E; Palau, A; Granados, X; Puig, T; Obradors, X; Amoros, J; Carrera, M

2005-01-01

A method for determining simultaneously the inter- and intra-grain critical currents has been developed in welded YBa 2 Cu 3 O 7 (YBCO) ceramics by solving the Inverse Problem for local maps of the magnetic field in the remanent state. From that current distribution, the current density flowing through the superconducting weld as well as the current density circulating inside the grains can be deduced. The method is discussed and it is applied to several examples of YBCO/Ag/YBCO welds. The results obtained show that it is possible to obtain superconducting joints with a quality at the same level as that of the starting material

Technique of Critical Current Density Measurement of Bulk Superconductor with Linear Extrapolation Method

International Nuclear Information System (INIS)

Adi, Wisnu Ari; Sukirman, Engkir; Winatapura, Didin S.

2000-01-01

Technique of critical current density measurement (Jc) of HTc bulk ceramic superconductor has been performed by using linear extrapolation with four-point probes method. The measurement of critical current density HTc bulk ceramic superconductor usually causes damage in contact resistance. In order to decrease this damage factor, we introduce extrapolation method. The extrapolating data show that the critical current density Jc for YBCO (123) and BSCCO (2212) at 77 K are 10,85(6) Amp.cm - 2 and 14,46(6) Amp.cm - 2, respectively. This technique is easier, simpler, and the use of the current flow is low, so it will not damage the contact resistance of the sample. We expect that the method can give a better solution for bulk superconductor application. Key words. : superconductor, critical temperature, and critical current density

Critical location identification and vulnerability analysis of interdependent infrastructure systems under spatially localized attacks

International Nuclear Information System (INIS)

Ouyang, Min

2016-01-01

Infrastructure systems are usually spatially distributed in a wide area and are subject to many types of hazards. For each type of hazards, modeling their direct impact on infrastructure components and analyzing their induced system-level vulnerability are important for identifying mitigation strategies. This paper mainly studies spatially localized attacks that a set of infrastructure components located within or crossing a circle shaped spatially localized area is subject to damage while other components do not directly fail. For this type of attacks, taking interdependent power and gas systems in Harris County, Texas, USA as an example, this paper proposes an approach to exactly identify critical locations in interdependent infrastructure systems and make pertinent vulnerability analysis. Results show that (a) infrastructure interdependencies and attack radius largely affect the position of critical locations; (b) spatially localized attacks cause less vulnerability than equivalent random failures; (c) in most values of attack radius critical locations identified by considering only node failures do not change when considering both node and edge failures in the attack area; (d) for many values of attack radius critical locations identified by topology-based model are also critical from the flow-based perspective. - Highlights: • We propose a method to identify critical locations in interdependent infrastructures. • Geographical interdependencies and attack radius largely affect critical locations. • Localized attacks cause less vulnerability than equivalent random failures. • Whether considering both node and edge failures affects critical locations. • Topology-based critical locations are also critical from flow-based perspective.

Oscillation of Critical Current by Gate Voltage in Cooper Pair Transistor

International Nuclear Information System (INIS)

Kim, N.; Cheong, Y.; Song, W.

2010-01-01

We measured the critical current of a Cooper pair transistor consisting of two Josephson junctions and a gate electrode. The Cooper pair transistors were fabricated by using electron-beam lithography and double-angle evaporation technique. The Gate voltage dependence of critical current was measured by observing voltage jumps at various gate voltages while sweeping bias current. The observed oscillation was 2e-periodic, which shows the Cooper pair transistor had low level of quasiparticle poisoning.

Processing and critical currents of high-Tc superconductor wires

International Nuclear Information System (INIS)

Krauth, H.; Heine, K.; Tenbrink, J.

1991-01-01

High-Tc superconductors are expected to have a major impact on magnet and energy technology. For technical applications they have to fulfill the requirement of carrying sufficient current at a critical current density of the order of 10 5 A/cm 2 at operating temperature and magnetic field. At 77 K these values have not been achieved yet in bulk material or wires due to weak link problems and flux creep effects. Progress made so far and remaining problems will be discussed in detail concentrating on problems concerning development of technical wires. In Bi-based materials technically interesting critical current densities could be achieved at 4.2 K in fields above 20 T (1,2), rendering possible the use of such material for very high field application. (orig.)

Improvement of critical currents in Bi-2223 bulk superconductors

International Nuclear Information System (INIS)

Eujen, R.; Brauer, D.J.; Huedepohl, J.

1991-01-01

Potential applications of the high-Tc superconductors for energy transport or high-field magnets require high critical current densities. A limiting factor in polycrystalline oxidic materials is the quality of the grain boundaries. Weak links have been made responsible for the steep decrease in the critical current density j c upon application of even weak magnetic fields of YBa CuO whereas flux creep seems to dominate the obtainable j c values for the Bi-Sr-Ca-Cu-O system (BSCCO) at 77 K. In the lead containing material (BPSCCO) the formation of a porous microstructure is enhanced by the platelike shape of the crystals. Special techniques such as powder-in-tube, hot isostatic pressing, zone melting or application of fluxes have been used in order to improve the grain contacts. A positive influence of fluxes on j c , e.g. by addition of Ca 2 CuO 3 or Ag 2 O, has been reported. In this study we have investigated the influence of various compositions and conditions on the formation of the BSCCO-2223 phase (T c ca. 107 K), the critical current density j c , and the magnet field dependence of the a.c. susceptibility. (orig.)

Non-monotonic field dependence of critical current in composite superconductors

International Nuclear Information System (INIS)

Andrianov, V.V.; Baev, V.P.; Ivanov, S.S.

1982-01-01

The nonmonotonic field dependence of critical current Im(B/sub a/ in composite superconductors is investigated experimentally for current and field varying simultaneously with final rates I and B/sub a/

Electromigration kinetics and critical current of Pb-free interconnects

Energy Technology Data Exchange (ETDEWEB)

Lu, Minhua; Rosenberg, Robert [IBM T. J. Watson Research Center, Yorktown Heights, New York 10598 (United States)

2014-04-07

Electromigration kinetics of Pb-free solder bump interconnects have been studied using a single bump parameter sweep technique. By removing bump to bump variations in structure, texture, and composition, the single bump sweep technique has provided both activation energy and power exponents that reflect atomic migration and interface reactions with fewer samples, shorter stress time, and better statistics than standard failure testing procedures. Contact metallurgies based on Cu and Ni have been studied. Critical current, which corresponds to the Blech limit, was found to exist in the Ni metallurgy, but not in the Cu metallurgy. A temperature dependence of critical current was also observed.

Critical current studies on fine filamentary NbTi accelerator wires

International Nuclear Information System (INIS)

Garber, M.; Sabatini, R.L.; Sampson, W.B.; Suenaga, M.

1986-01-01

The magnets for the Superconducting Super Collider, a high energy proton colliding beam accelerator, require a superconductor with very high current density (> 2400 A/mm 2 at 5 T) and very small filaments ( about 2μ m in diameter). Previous work has shown that by controling the formation of Cu 4 Ti compound particles on the filament surfaces it is possible to make fine filamentary NbTi wire with high critical current density. The performance of multi-filamentary wire is characterized by the current density and the quantity ''n'' which describes the superconducting-normal transition. Micrographs of wires having high J /SUB c/ and high n show smooth, uniform filaments. Recently wires of very high critical current and high n have been produced in experimental quantities by commercial manufacturers

Critical current studies on fine filamentary NbTi accelerator wires

International Nuclear Information System (INIS)

Garber, M.; Suenaga, M.; Sampson, W.B.; Sabatini, R.L.

1985-01-01

The magnets for the Superconductig Super Collider, a high energy proton colliding beam accelerator, require a superconductor with very high current density (>2400 A/mm 2 at 5 T) and very small filaments (approx. 2μm in diameter). Previous work has shown that by controlling the formation of Cu 4 Ti compound particles on the filament surfaces it is possible to make fine filamentary NbTi wire with high critical current density. The performance of multi-filamentary wire is characterized by the current density and the quantity ''n'' which describes the superconducting-normal transition. Micrographs of wires having high J/sub c/ and high n show smooth, uniform filaments. Recently wires of very high critical current and high n have been produced in experimental quantities by commercial manufactures

Electric field effect on the critical current of SNS-contact

International Nuclear Information System (INIS)

Rakhmanov, A.L.; Rozhkov, A.V.

1995-01-01

Electric field effect on the SNS-contact critical current is investigated in the Ginzburg-Landau theory approximation. It is shown that the electric field may cause a notable increase of the contact critical current especially if the sample temperature is close to the temperature of a superconducting transition of T sc normal layer. Electric field effect is increased with the reduction of film thickness, but it can strong enough for thick films as well at temperature close to T sc . 11 refs.; 4 figs

Critical current density for spin transfer torque switching with composite free layer structure

OpenAIRE

You, Chun-Yeol

2009-01-01

Critical current density of composite free layer (CFL) in magnetic tunneling junction is investigated. CFL consists of two exchange coupled ferromagnetic layers, where the coupling is parallel or anti-parallel. Instability condition of the CFL under the spin transfer torque, which is related with critical current density, is obtained by analytic spin wave excitation model and confirmed by macro-spin Landau-Lifshitz-Gilbert equation. The critical current densities for the coupled two identical...

Crack problem in superconducting cylinder with exponential distribution of critical-current density

Science.gov (United States)

Zhao, Yufeng; Xu, Chi; Shi, Liang

2018-04-01

The general problem of a center crack in a long cylindrical superconductor with inhomogeneous critical-current distribution is studied based on the extended Bean model for zero-field cooling (ZFC) and field cooling (FC) magnetization processes, in which the inhomogeneous parameter η is introduced for characterizing the critical-current density distribution in inhomogeneous superconductor. The effect of the inhomogeneous parameter η on both the magnetic field distribution and the variations of the normalized stress intensity factors is also obtained based on the plane strain approach and J-integral theory. The numerical results indicate that the exponential distribution of critical-current density will lead a larger trapped field inside the inhomogeneous superconductor and cause the center of the cylinder to fracture more easily. In addition, it is worth pointing out that the nonlinear field distribution is unique to the Bean model by comparing the curve shapes of the magnetization loop with homogeneous and inhomogeneous critical-current distribution.

Numerical prediction of a dip effect in the critical current density

International Nuclear Information System (INIS)

Al Khawaja, U.; Benkraouda, M.; Obaidat, I.M.

2007-01-01

We have conducted extensive series of molecular dynamic simulations on the properties of the critical current density in systems with periodic square arrays of pinning sites. The density of the pinning sites was kept fixed while the density of vortices, pinning strength, and temperature were varied several times. At zero temperature, we have observed a substantial dip in the critical current density that occurs only at a fixed value of the vortex density and for specific values of pinning strength. We have found that the occurrence of the dip depends mainly on the initial positions of the vortices with respect to the positions of the pinning sites. At the dip, we have found that the interstitial vortices form moving channels leading to the observed drop in the critical current density

Critical current anomaly at the topological quantum phase transition in a Majorana Josephson junction

Energy Technology Data Exchange (ETDEWEB)

Huang, Hong [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Liang, Qi-Feng [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Yao, Dao-Xin, E-mail: yaodaox@mail.sysu.edu.cn [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China); Wang, Zhi, E-mail: physicswangzhi@gmail.com [School of Physics, Sun Yat-sen University, Guangzhou 510275 (China)

2017-06-28

Majorana bound states in topological Josephson junctions induce a 4π period current-phase relation. Direct detection of the 4π periodicity is complicated by the quasiparticle poisoning. We reveal that Majorana bound states are also signaled by the anomalous enhancement on the critical current of the junction. We show the landscape of the critical current for a nanowire Josephson junction under a varying Zeeman field, and reveal a sharp step feature at the topological quantum phase transition point, which comes from the anomalous enhancement of the critical current at the topological regime. In multi-band wires, the anomalous enhancement disappears for an even number of bands, where the Majorana bound states fuse into Andreev bound states. This anomalous critical current enhancement directly signals the existence of the Majorana bound states, and also provides a valid signature for the topological quantum phase transition. - Highlights: • We introduce the critical current step as a signal for the topological quantum phase transition. • We study the quantum phase transition in the topological nanowire under a rotating Zeeman field. • We show that the critical current anomaly gradually disappears for systems with more sub-bands.

Induced critical current density limit of Ag sheathed Bi-2223 tape conductor

International Nuclear Information System (INIS)

Ogiwara, H.; Satou, M.; Yamada, Y.; Kitamura, T.; Hasegawa, T.

1994-01-01

The authors have already reported the best critical current density of 66,000 A/cm 2 with an Ag sheathed Bi-2223 tape conductor. The Brick-wall model is for explaining the current transport mechanism of this conductor. The model has its roots in the fact that the Bi-2223 tape core is a complicated stack of crystals which have a mica-flake structure. The orientation of the crystals which have a mica-flake structure. The orientation of the crystals seriously affects the current transport capability. Moreover, the contacts between the stacking crystals are very important. The transport current flows dividing into many branch paths. Under high magnetic field, the different paths experienced different electromagnetic forces. Differences between the electromagnetic forces on the different crystals can affect the contacts so as to increase resistivity and decrease overall critical current density of the tape. This effect can foretell the limit of the critical current density obtainable with these kinds of conductors

Critical current measurement in superconducting rings using an automatic inductive technique

International Nuclear Information System (INIS)

Gonzalez-Jorge, H.; Linares, B.; Quelle, I.; Carballo, E.; Romani, L.; Domarco, G.

2007-01-01

A measurement technique was developed to identify the critical current of superconducting rings. It is based on the detection of the voltage on a secondary coil when the current induced in the superconductor by a primary one go beyond to the critical value. The technique uses a DC power supply to control the AC current circulating by the primary circuit. Such circuit mainly consists on an AC power supply which gives a constant AC voltage, a primary inducting coil and a control coil with iron core. The AC current circulating by this circuit is modified with the change in the impedance of the control coil due to the fact of the DC current supplied by the power supply in parallel with it

Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples

International Nuclear Information System (INIS)

Passos, W.A.C.

2016-01-01

This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa_2Cu_3O_7_-_δ sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T_c of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

Critical current of Josephson contacts with accidental position of vortexes

International Nuclear Information System (INIS)

Fistul', M.V.

1989-01-01

Josephson contact critical current dependence on magnetic field under different concentrations of Abrikosov vortices (AV) in superconducting shores is found. Pinned vortex concentration as well as correlation in the vortex position can be determined by Josephson current dependence on magnetic field

Engineering Critical Current Density Improvement in Ag- Bi-2223 Tapes

DEFF Research Database (Denmark)

Wang, W. G.; Seifi, Behrouz; Eriksen, Morten

2000-01-01

Ag alloy sheathed Bi-2223 multifilament tapes were produced by the powder-in-tube method. Engineering critical current density improvement has been achieved through both enhancement of critical current density by control of the thermal behavior of oxide powder and by an increase of the filling...... factor of the tapes. Phase evolution at initial sintering stage has been studied by a quench experiment in Ag-Bi-2223 tapes. The content, texture, and microstructure of various phases were determined by XRD and SEM. A novel process approach has been invented in which square wire was chosen rather than...

Critical current in the Integral Quantum Hall Effect

International Nuclear Information System (INIS)

Kostadinov, I.Z.

1985-11-01

A multiparticle theory of the Integral Quantum Hall Effect (IQHE) was constructed operating with pairs wave function as an order parameter. The IQHE is described with bosonic macroscopic states while the fractional QHE with fermionic ones. The calculation of the critical current and Hall conductivity temperature dependence is presented. (author)

Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films

Science.gov (United States)

Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.;

Influence of vortex-vortex interaction on critical currents across low-angle grain boundaries in YBa2Cu3O7-δ thin films

Science.gov (United States)

Albrecht, J.; Leonhardt, S.; Kronmüller, H.

2001-01-01

Low-angle grain boundaries with misorientation angles θ<5° in optimally doped thin films of YBa2Cu3O7-δ are investigated by magneto-optical imaging. By using a numerical inversion scheme of Biot-Savart's law, the critical current density across the grain boundary can be determined with a spatial resolution of about 5μm. Detailed investigation of the spatially resolved flux density and current density data shows that the current density across the boundary varies with varying local flux density. Combining the corresponding flux and current pattern, it is found that there exists a universal dependency of the grain boundary current on the local flux density. Considering the magnetic vortex-vortex interaction in and in the vicinity of the grain boundary, a model is developed that is able to describe the experimental data.

Critical currents and superconductivity ferromagnetism coexistence in high-Tc oxides

CERN Document Server

Khene, Samir

2016-01-01

The book comprises six chapters which deal with the critical currents and the ferromagnetism-superconductivity coexistence in high-Tc oxides. It begins by gathering key data for superconducting state and the fundamental properties of the conventional superconductors, followed by a recap of the basic theories of superconductivity. It then discusses the differences introduced by the structural anisotropy on the Ginzburg-Landau approach and the Lawrence-Doniach model before addressing the dynamics of vortices and the ferromagnetism-superconductivity coexistence in high-Tc oxides, and provides an outline of the pinning phenomena of vortices in these materials, in particular the pinning of vortices by the spins. It elucidates the methods to improve the properties of superconducting materials for industrial applications. This optimization aims at obtaining critical temperatures and densities of critical currents at the maximum level possible. Whereas the primary objective is the basic mechanisms pushing the superco...

Strand critical current degradation in $Nb_{3}$ Sn Rutherford cables

CERN Document Server

Barzi, E; Higley, H C; Scanlan, R M; Yamada, R; Zlobin, A V

2001-01-01

Fermilab is developing 11 Tesla superconducting accelerator magnets based on Nb/sub 3/Sn superconductor. Multifilamentary Nb/sub 3/Sn strands produced using the modified jelly roll, internal tin, and powder-in-tube technologies were used for the development and test of the prototype cable. To optimize the cable geometry with respect to the critical current, short samples of Rutherford cable with packing factors in the 85 to 95% range were fabricated and studied. In this paper, the results of measurements of critical current, n-value and RRR made on the round virgin strands and on the strands extracted from the cable samples are presented. (5 refs).

Critical current characteristics in high T/sub c/ oxide superconductors

International Nuclear Information System (INIS)

Matsushita, T.; Ni, B.

1989-01-01

Critical current densities are theoretically estimated for single-crystalline thin films, polycrystalline bulk materials with oriented and random textures of superconducting oxides. The percolation theory is used and the effect of depression of the transport current through grain boundaries is taken into account. A comparison is made with existing experimental results

Critical Analysis of 2012 Local Elections in Bosnia-Herzegovina

Directory of Open Access Journals (Sweden)

Mirsad Karic

2013-03-01

Full Text Available This paper provides a critical analyzes of 2012 local elections in Bosnia-Herzegovina. Since 1995 the local elections and its political and electoral system have been based on the Dayton Peace Agreement (DPA. According to DPA Bosnia-Herzegovina has the multiparty system and regular and free elections. These local elections were held amidst continuously renewed political turmoil at the cantonal, entity and state levels. 2012 local elections results have shown that the HDZ and SDA continued to dominate politics at the local level in the Federation of BiH while in the RS, position of SNSD has been strongly shaken by very good performance of SDS. The SDA won majority of votes in Bosniak majority areas while SDS and HDZ secured their votes in the Serb and Croat majority areas respectively. In the Federation of BiH, SDP and SBB suffered dramatic fall in votes comparing to the last general elections while in the RS, SNSD, which has dominated politics since 2006 lost significant number of votes, mayoral posts and municipality seats to SDS and some other political parties such as PDP, SP and DNS.

A Monte Carlo simulation on critical current distribution of bent-damaged multifilamentary Bi2223 composite tape

International Nuclear Information System (INIS)

Ochiai, S.; Okuda, H.; Fujimoto, M.; Shin, J.K.; Oh, S.S.; Ha, D.W.

2011-01-01

We simulate critical current distribution of bent-damaged Bi2223 composite tape. We use a Monte Carlo method and a damage evolution model for simulation. With the present simulation approach, experimental results are described well. Critical current distribution stems mainly from difference in damage evolution. It was attempted to reproduce the measured critical current (I c ) distributions of the Bi2223 composite tape bent by 0-0.833% by simulation. Simulation was carried out with a Monte Carlo method in combination with a model that correlates the critical current to damage evolution. Two variables that differ from specimen to specimen were input in the simulation. One was the damage strain parameter, with which the difference in extent of damage among specimens was expressed. Another was the original critical current (I c0 ) values at zero bending strain. With the present simulation approach, the measured distributions of critical current at various bending strains, and the measured variations of average and coefficient of variation of critical current values with increasing bending strain were reproduced well.

Prediction of critical heat flux by a new local condition hypothesis

International Nuclear Information System (INIS)

Im, J. H.; Jun, K. D.; Sim, J. W.; Deng, Zhijian

1998-01-01

Critical Heat Flux(CHF) was predicted for uniformly heated vertical round tube by a new local condition hypothesis which incorporates a local true steam quality. This model successfully overcame the difficulties in predicted the subcooled and quality CHF by the thermodynamic equilibrium quality. The local true steam quality is a dependent variable of the thermodynamic equilibrium quality at the exit and the quality at the Onset of Significant Vaporization(OSV). The exit thermodynamic equilibrium quality was obtained from the heat balance, and the quality at OSV was obtained from the Saha-Zuber correlation. In the past CHF has been predicted by the experimental correlation based on local or non-local condition hypothesis. This preliminary study showed that all the available world data on uniform CHF could be predicted by the model based on the local condition hypothesis

Angular and magnetic field dependences of critical current in irradiated YBaCuO single crystals

International Nuclear Information System (INIS)

Petrusenko, Yu.

2010-01-01

The investigation of mechanisms responsible for the current-carrying capability of irradiated high-temperature superconductors (HTSC) was realized. For the purpose, experiments were made to investigate the effect of point defects generated by high-energy electron irradiation on the critical temperature and the critical current in high-Tc superconducting single crystals YBa 2 Cu 3 O 7-x . The transport current density measured in HTSC single crystals YBa 2 Cu 3 O 7-x by the dc-method was found to exceed 80000 A/cm 2 . The experiments have demonstrated a more than 30-fold increase in the critical current density in single crystals irradiated with 2.5 MeV electrons to a dose of 3·10 18 el/cm 2 . Detailed studies were made into the anisotropy of critical current and the dependence of critical current on the external magnetic field strength in irradiated single crystals. A high efficiency of point defects as centers of magnetic vortex pinning in HTSC single crystals was first demonstrated.

Phonon-induced enhancements of the energy gap and critical current in superconducting aluminum

International Nuclear Information System (INIS)

Seligson, D.

1983-01-01

The enhancement of the energy gap, Δ, and critical current, i/sub c/, in superconducting aluminum thin films were under the influence of 8 to 10 GHz phonons. The phonons were generated by piezoelectric transduction of a 1 kW microwave pulse of about 1 μsec duration. By means of a quartz delay line, the phonons were allowed to enter the aluminum only after the microwaves had long since disappeared. The critical current was measured in long narrow Al strips, in which the current flow is 1-dimensional and well described by Ginsburg-Landau theory. To measure Δ the Al film was used as one electrode in a superconductor-insulator-superconductor tunnel junction whose current-voltage characteristic gave Δ directly. For the measurements of i/sub c/, the total critical current was measured in the presence of the phonon perturbation. For the measurements of Δ the change of Δ away from its equilibrium value was measured. In both cases the first measurements of enhancement of these macroscopic variables under phonon irradiation is reported. The gap-enhancement was found to be in good agreement with theory, but only for relatively and surprisingly low input power. The critical current measurements are predicted to be in rough agreement with the Δ measurements but this was not observed

Local effect of equilibrium current on tearing mode stability

International Nuclear Information System (INIS)

Cozzani, F.

1985-12-01

The local effect of the equilibrium current on the linear stability of low poloidal number tearing modes in tokamaks is investigated analytically. The plasma response inside the tearing layer is derived from fluid theory and the local equilibrium current is shown to couple to the mode dynamics through its gradient, which is proportional to the local electron temperature gradient under the approximations used in the analysis. The relevant eigenmode equations, expressing Ampere's law and the plasma quasineutrality condition, respectively, are suitably combined in a single integral equation, from which a variational principle is formulated to derive the mode dispersion relations for several cases of interest. The local equilibrium current is treated as a small perturbation of the known results for the m greater than or equal to 2 and the m = 1 tearing modes in the collisional regime, and the m greater than or equal to 2 tearing mode in the semicollisional regime; its effect is found to enhance stabilization for the m greater than or equal to 2 drift-tearing mode in the collisional regime, whereas the m = 1 growth rate is very slightly increased and the stabilizing effect of the parallel thermal conduction on the m greater than or equal to 2 mode in the semicollisional regime is slightly reduced

Influence of anisotropy and pinning centers on critical current properties in Bi-2212 superconductors

International Nuclear Information System (INIS)

Haraguchi, T.; Takayama, S.; Kiuchi, M.; Otabe, E.S.; Matsushita, T.; Yasuda, T.; Okayasu, S.; Uchida, S.; Shimoyama, J.; Kishio, K.

2006-01-01

The critical current density in Bi-2212 superconductors with various anisotropies irradiated by heavy ions was investigated in the medium temperature region to understand the effects of defect size and the anisotropy of the superconductor. It was found that the critical current density and the irreversibility field were larger for the specimen with larger defect and/or with smaller anisotropy. Introduction of stronger pinning centers and the optimization of the doping condition to improve the dimensionality are desired for further improvement of the critical current properties

Interlaboratory comparison on high-temperature superconductor critical-current measurements

International Nuclear Information System (INIS)

Wiejaczka, J.A.; Goodrich, L.F.

1997-01-01

An extensive interlaboratory comparison was conducted on high temperature superconductor (HTS) critical-current measurements. This study was part of an international cooperative effort through the Versailles Project on Advanced Materials and Standards (VAMAS). The study involved six US laboratories that are recognized leaders in the field of HTS. This paper includes the complete results from this comparison of critical-current measurements on Ag-sheathed Bi 2 Sr 2 Ca 2 Cu 3 O 10-x (2223) tapes. The effects of sample characteristics, specimen mounting, measurement technique, and specimen damage were studied. The future development of a standard HTS measurement method is also discussed. Most of the evolution of this emerging technology has occurred in improvement of the performance of the conductors. The successful completion of this interlaboratory comparison is an important milestone in the evolution of HTS technology and marks a level of maturity that the technology has reached

Analytical model of the critical current of a bent Nb3Sn strand

International Nuclear Information System (INIS)

Koizumi, Norikiyo; Murakami, Haruyuki; Hemmi, Tsutomu; Nakajima, Hideo

2011-01-01

The critical current performance of a large Nb 3 Sn cable-in-conduit conductor (CICC) was degraded by periodic bending of strands due to a large transverse electromagnetic force. The degradation of each strand due to this bending should be evaluated in calculations of the critical current of a CICC, but a suitable model has not been developed yet. Therefore, the authors have developed a new analytical model which takes into account plastic deformation of copper and bronze and filament breakage. The calculated results were compared with test results for uniformly bent Nb 3 Sn bronze-route strands. The calculated results assuming a high transverse resistance model (HTRM) show good agreement with the test results, a finding which confirms the validity of the model. Because of a much shorter calculation time than for numerical simulation, the developed model seems much more practical for use in calculating the critical current performance of a Nb 3 Sn CICC. In addition, simulation results show that since the neutral axis of a bent strand shifts to the compressive side due to plastic deformation of the copper and bronze, and/or filament breakage, the strand is elongated by bending. This elongation may enhance the strand's critical current performance. Moreover, the calculated results indicate that the dependence of the critical current on the bending strain is affected by the bending history if the strand is excessively bent, especially when filaments are broken. In a real magnet, since a strand in a CICC is normally subject to the maximum electromagnetic force prior to an evaluation of its performance at a lower electromagnetic force, the effect of over-bending should be taken into account in calculations of its critical current performance, especially when filament breakage occurs.

Localized persistent spin currents in defect-free quasiperiodic rings with Aharonov–Casher effect

International Nuclear Information System (INIS)

Qiu, R.Z.; Chen, C.H.; Cheng, Y.H.; Hsueh, W.J.

2015-01-01

We propose strongly localized persistent spin current in one-dimensional defect-free quasiperiodic Thue–Morse rings with Aharonov–Casher effect. The results show that the characteristics of these localized persistent currents depend not only on the radius filling factor, but also on the strength of the spin–orbit interaction. The maximum persistent spin currents in systems always appear in the ring near the middle position of the system array whether or not the Thue–Morse rings array is symmetrical. The magnitude of the persistent currents is proportional to the sharpness of the resonance peak, which is dependent on the bandwidth of the allowed band in the band structure. The maximum persistent spin currents also increase exponentially as the generation order of the system increases. - Highlights: • Strongly localized persistent spin current in quasiperiodic AC rings is proposed. • Localized persistent spin currents are much larger than those produced by traditional mesoscopic rings. • Characteristics of the localized persistent currents depend on the radius filling factor and SOI strength. • The maximum persistent current increases exponentially with the system order. • The magnitude of the persistent currents is related to the sharpness of the resonance

Rationing critical care medicine: recent studies and current trends.

Science.gov (United States)

Ward, Nicholas S

2005-12-01

This paper reviews the literature on the rationing of critical care resources. Although much has been written about the concept of rationing, there have been few scientific studies as to its prevalence. A recent meta-analysis reviewed all previously published studies on rationing access to intensive care units but little is known about practices within the intensive care unit. Much literature in the past few years has focused on the growing use of critical care resources and projections for the future. Several authors suggest there may be a crisis in financial or personnel resources if some rationing does not take place. Other papers have argued that the methods of rationing critical care previously proposed, such as limiting the care of dying patients or using cost-effectiveness analysis to determine care, may not be effective or viewed as ethical by some. Finally, several recent papers review how critical care is practiced and allocated in India and Asian countries that already practice open rationing in their health care systems. There is currently no published evidence that overt rationing is taking place in critical care medicine. There is growing evidence that in the future, the need for critical care may outstrip financial resources unless some form of rationing takes place. It is also clear from the literature that choosing how to ration critical care will be a difficult task.

Magnetic field oscillations of the critical current in long ballistic graphene Josephson junctions

Science.gov (United States)

Rakyta, Péter; Kormányos, Andor; Cserti, József

2016-06-01

We study the Josephson current in long ballistic superconductor-monolayer graphene-superconductor junctions. As a first step, we have developed an efficient computational approach to calculate the Josephson current in tight-binding systems. This approach can be particularly useful in the long-junction limit, which has hitherto attracted less theoretical interest but has recently become experimentally relevant. We use this computational approach to study the dependence of the critical current on the junction geometry, doping level, and an applied perpendicular magnetic field B . In zero magnetic field we find a good qualitative agreement with the recent experiment of M. Ben Shalom et al. [Nat. Phys. 12, 318 (2016), 10.1038/nphys3592] for the length dependence of the critical current. For highly doped samples our numerical calculations show a broad agreement with the results of the quasiclassical formalism. In this case the critical current exhibits Fraunhofer-like oscillations as a function of B . However, for lower doping levels, where the cyclotron orbit becomes comparable to the characteristic geometrical length scales of the system, deviations from the results of the quasiclassical formalism appear. We argue that due to the exceptional tunability and long mean free path of graphene systems a new regime can be explored where geometrical and dynamical effects are equally important to understand the magnetic field dependence of the critical current.

Experiment of enhancing critical current in Bi-2223/Ag tape by means of ferromagnetic shielding

Energy Technology Data Exchange (ETDEWEB)

Alamgir, A.K.M. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China)]. E-mail: alam643@hotmail.com; Gu, C. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China); Han, Z. [Applied Superconductivity Research Center, Department of Physics, Tsinghua University, Beijing 100084 (China)

2005-11-15

Critical current in multifilamentary Ag-sheath Bi-2223 tape is enhanced to some extent by means of thin and narrow coating of pure nickel. The concept of enhancing critical current is based on the magnetic shielding effect resulting in redirection of self-field flux lines. The Ni coating was introduced at the edge regime of the tape in order to redirect the perpendicular component of self-field lines which is severe at the edges. Critical current in a typical Ag-sheath Bi-2223 tape was enhanced up to {approx}11% by 50 {mu}m thick and 0.4 mm long Ni coating without any change of self-field loss. This fact reveals that additional ferromagnetic loss could be compensated by the shielding effect and increased critical current of the tape. The degree of enhancement in critical current as well as ferromagnetic impact on ac losses depend on the length and thickness of ferromagnetic coating introduced. Therefore, it is very important to control the geometry of ferromagnetic coating in order to balance the critical current and ac loss for optimum superconductor performance. Introduction of ferromagnetic coating and its effect on electromagnetic properties in multifilamentary Bi-2223/Ag tape will be reported in this article.

Experiment of enhancing critical current in Bi-2223/Ag tape by means of ferromagnetic shielding

International Nuclear Information System (INIS)

Alamgir, A.K.M.; Gu, C.; Han, Z.

2005-01-01

Critical current in multifilamentary Ag-sheath Bi-2223 tape is enhanced to some extent by means of thin and narrow coating of pure nickel. The concept of enhancing critical current is based on the magnetic shielding effect resulting in redirection of self-field flux lines. The Ni coating was introduced at the edge regime of the tape in order to redirect the perpendicular component of self-field lines which is severe at the edges. Critical current in a typical Ag-sheath Bi-2223 tape was enhanced up to ∼11% by 50 μm thick and 0.4 mm long Ni coating without any change of self-field loss. This fact reveals that additional ferromagnetic loss could be compensated by the shielding effect and increased critical current of the tape. The degree of enhancement in critical current as well as ferromagnetic impact on ac losses depend on the length and thickness of ferromagnetic coating introduced. Therefore, it is very important to control the geometry of ferromagnetic coating in order to balance the critical current and ac loss for optimum superconductor performance. Introduction of ferromagnetic coating and its effect on electromagnetic properties in multifilamentary Bi-2223/Ag tape will be reported in this article

Critical current density analysis of ex situ MgB2 wire by in-field and temperature Hall probe imaging

International Nuclear Information System (INIS)

Bartolome, E; Granados, X; Cambel, V; Fedor, J; Kovac, P; Husek, I

2005-01-01

The irreversible magnetic behaviour at different temperatures of an ex situ Fe-alloy/MgB 2 wire, exhibiting a granular compositional distribution, was studied using an in-field, high resolution Hall probe imaging system. Quantitative information about the local current density was obtained by solving the Biot-Savart inversion problem. The flux penetration and current distribution maps obtained can be attributed to a inhomogeneous compositional 'plum-cake-like' system, consisting of large, isolated MgB 2 agglomerations embedded in a matrix of finely distributed MgB 2 +MgO. The critical current densities within the grains and their evolution with the applied magnetic field and temperature have been obtained, and compared to the mean J c (H,T) in the matrix

Comparison of growth texture in round Bi2212 and flat Bi2223 wires and its relation to high critical current density development

OpenAIRE

Kametani, F.; Jiang, J.; Matras, M.; Abraimov, D.; Hellstrom, E. E.; Larbalestier, D. C.

2015-01-01

Why Bi2Sr2CaCu2Ox (Bi2212) allows high critical current density Jc in round wires rather than only in the anisotropic tape form demanded by all other high temperature superconductors is important for future magnet applications. Here we compare the local texture of state-of-the-art Bi2212 and Bi2223 ((Bi,Pb)2Sr2Ca2Cu3O10), finding that round wire Bi2212 generates a dominant a-axis growth texture that also enforces a local biaxial texture (FWHM

Tuning of tunneling current noise spectra singularities by localized states charging

OpenAIRE

Mantsevich, V. N.; Maslova, N. S.

2008-01-01

We report the results of theoretical investigations of tunneling current noise spectra in a wide range of applied bias voltage. Localized states of individual impurity atoms play an important role in tunneling current noise formation. It was found that switching "on" and "off" of Coulomb interaction of conduction electrons with two charged localized states results in power law singularity of low-frequency tunneling current noise spectrum ($1/f^{\\alpha}$) and also results on high frequency com...

Effect of stress on the critical current of NbTi multifilamentary composite wire

International Nuclear Information System (INIS)

Ekin, J.W.; Fickett, F.R.; Clark, A.F.

1977-01-01

Superconducting composites within large-scale magnets can be subjected to high stresses. These stresses arise from several sources, chief among them being the winding tension and prestressing during construction of the magnet, the thermomechanical forces incurred during thermal cycling to cryogenic temperatures, and especially in large-scale systems, the magnetomechanical forces generated when the magnet is energized. Typically, data on the critical-current characteristics of superconducting composites are obtained on wires that are in an unstressed state. Very little is known, however, about how the critical current behaves in wires experiencing stresses of the type described above. To measure these effects, short sample critical current tests were made under conditions simultaneously simulating the mechanical and magnetic environments of high-field superconducting magnets. The program was initiated both to form a basis for the fundamental understanding of stress effects on superconductor stability and to provide engineering data for optimizing design and construction of high-field magnets. The preliminary results indicate that NbTi multifilamentary superconducting composite wires are not characterized by a single critical current vs. field curve, but rather by a family of curves, each corresponding to a different operating stress level

Critical current density in railgrun accelerators with composite electrodes

International Nuclear Information System (INIS)

Stankevich, S.V.; Shvetsov, G.A.

1995-01-01

The present paper is intended to study the possibilities of increasing the critical current density in railgun accelerators using composite electrodes of various structure. Before proceeding to the analysis this way, it should be noted that the requirements for materials selected for the rails go beyond the values of the current density. In real practice account should be taken of the technological problems concerned with the production of the electrodes, as well as of those concerned with the railgun performance, including the multishot life

Preparation and characterization of high-Tc superconducting thin films with high critical current densities

International Nuclear Information System (INIS)

Vase, P.

1991-08-01

The project was carried out in relation to possible cable and electronics applications of high-T c materials. Laser ablation was used as the deposition technique because of its stoichiometry conservation. Films were made in the YBa 2 Cu 3 O 7 compound due to its relatively simple stoichiometry compared to other High-T c compounds. Much attention was paid to the critical current density. A very high critical current density was reached. By using texture analysis by X-ray diffraction, it was found that films with high critical current densities were epitaxial, while films with low critical current densities contained several crystalline orientations. Four techniques for patterning the films were used - photo lithography and wet etch, laser ablation lithography, laser writing and electron beam lithography and ion milling. Sub-micron patterning has been demonstrated without degradation of the superconducting properties. The achieved patterning resolution is sufficient for preparation of many superconducting components. (AB)

Magnetic field dependence of the critical current density in YBa2Cu3Ox ceramics

International Nuclear Information System (INIS)

Zhukov, A.A.; Moshchalkov, V.V.; Komarkov, D.A.; Shabatin, V.P.; Gordeev, S.N.; Shelomov, D.V.

1989-01-01

Three magnetic field ranges corresponding to different critical current density j c behavior have been found out. They correlate with grain magnetization changes. The inverse critical current density is shown to depend linearly on the sample cross-section due to the magnetic field induced by the flowing current

Magnetization and critical currents of NbTi wires with fine filaments

International Nuclear Information System (INIS)

Ghosh, A.K.; Sampson, W.B.

1985-01-01

In high energy accelerators such as the SSC, the magnetization of the superconductor is an important component in determining the harmonic fields at injection (approx.0.3T). In an effort to reduce these residual fields, interest has focused on NbTi conductors with fine filaments which are expected to have a reduced magnetization as dictated by the critical state model. With this in view, the magnetization and critical currents were measured at 4.3K for a set of NbTi wires with filament diameters, d, ranging from 1.0 to 5.0 microns. The data show that, although the magnetization scales linearly with d, it does not do so with the product J/sub c/d for d less than 3 μm. However, at these d values, the critical transport current density, J/sub c/ of NbTi was observed to decrease rapidly as a function of d. The origin of this J/sub c/ degradation and its effect on the scaling of magnetization within the framework of the critical state model is explored. We also examine the question of the observed asymmetry of the hysteretic magnetization

Phonon-induced enhancement of the energy gap and critical current of superconducting aluminum films

International Nuclear Information System (INIS)

Seligson, D.; Clarke, J.

1983-01-01

Enhancements of the energy gap Δ and the critical current I/sub c/ have been induced in thin superconducting aluminum films near the transition temperature T/sub c/ by pulses of phonons at approximately 9 GHz. In terms of the change in temperature Vertical BardeltaT/T/sub c/Vertical Bar necessary to produce the same enhancement in equilibrium, the gap enhancement increased smoothly with phonon power at fixed temperature and decreasing temperature at fixed phonon power; however, very close to T/sub c/ the enhancement rolled off. At relatively low phonon powers, the data were in good agreement with the theory of Eckern, Schmid, Schmutz, and Schoen, but at higher power levels the data fell markedly below the predictions of the theory. The critical-current enhancements in terms of Vertical BardeltaT/T/sub c/Vertical Bar were always larger than the gap enhancements at the same temperature and phonon power. At fixed phonon power the critical-current enhancements were nearly independent of temperature, except very close to T/sub c/ where the enhancement became small. The inclusion of the nonequilibrium quasiparticle distribution and the kinetic energy of the supercurrent in the theory relating the critical-current enhancement to the gap enhancement did not resolve the discrepancies between the two enhancements. It appears likely that there is an additional mechanism for critical-current enhancement that has not yet been identified

Critical thresholds in flocking hydrodynamics with non-local alignment.

Science.gov (United States)

Tadmor, Eitan; Tan, Changhui

2014-11-13

We study the large-time behaviour of Eulerian systems augmented with non-local alignment. Such systems arise as hydrodynamic descriptions of agent-based models for self-organized dynamics, e.g. Cucker & Smale (2007 IEEE Trans. Autom. Control 52, 852-862. (doi:10.1109/TAC.2007.895842)) and Motsch & Tadmor (2011 J. Stat. Phys. 144, 923-947. (doi:10.1007/s10955-011-0285-9)) models. We prove that, in analogy with the agent-based models, the presence of non-local alignment enforces strong solutions to self-organize into a macroscopic flock. This then raises the question of existence of such strong solutions. We address this question in one- and two-dimensional set-ups, proving global regularity for subcritical initial data. Indeed, we show that there exist critical thresholds in the phase space of the initial configuration which dictate the global regularity versus a finite-time blow-up. In particular, we explore the regularity of non-local alignment in the presence of vacuum. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Spatially Localized Particle Energization by Landau Damping in Current Sheets

Science.gov (United States)

Howes, G. G.; Klein, K. G.; McCubbin, A. J.

2017-12-01

Understanding the mechanisms of particle energization through the removal of energy from turbulent fluctuations in heliospheric plasmas is a grand challenge problem in heliophysics. Under the weakly collisional conditions typical of heliospheric plasma, kinetic mechanisms must be responsible for this energization, but the nature of those mechanisms remains elusive. In recent years, the spatial localization of plasma heating near current sheets in the solar wind and numerical simulations has gained much attention. Here we show, using the innovative and new field-particle correlation technique, that the spatially localized particle energization occurring in a nonlinear gyrokinetic simulation has the velocity space signature of Landau damping, suggesting that this well-known collisionless damping mechanism indeed actively leads to spatially localized heating in the vicinity of current sheets.

Altering critical depinning current via domain wall pile-up in magnetic nanowires

International Nuclear Information System (INIS)

Geng, Liwei D.; Jin, Yongmei M.

2015-01-01

An important role of domain wall pile-up in current-driven domain wall depinning in magnetic nanowires is revealed using micromagnetic simulations. It is found that the critical current for domain wall depinning can be substantially reduced and conveniently tuned by controlling domain wall number in the pile-up at pinning site, in analogy to dislocation pile-up responsible for Hall–Petch effect in mechanical strength. Domain wall pinning and depinning at an s-shape bend is considered, and the effects of curvature and current crowding in magnetic circuit on domain wall behaviors are discussed. - Highlights: • Advance fundamental knowledge of current-driven domain wall phenomena. • Provide a novel approach to drastically reduce the critical depinning current. • Solve an outstanding problem of effective control of domain wall pinning/depinning. • Report appealing new findings of magnetic domain wall pile-up mechanism. • Overcome the limitations of materials properties for domain wall-based devices

Micromagnetic modeling of critical current oscillations in magnetic Josephson junctions

NARCIS (Netherlands)

golovchanskiy, I.A.; Bol'ginov, V.V.; Stolyarov, V.S.; Abramov, N.N.; Ben Hamida, A.; Emelyanova, O.V.; Stolyarov, B.S.; Kupriyanov, M..Y.; Golubov, Alexandre Avraamovitch; Ryazanov, V.V.

2016-01-01

In this work we propose and explore an effective numerical approach for investigation of critical current dependence on applied magnetic field for magnetic Josephson junctions with in-plane magnetization orientation. This approach is based on micromagnetic simulation of the magnetization reversal

Self-organized criticality revisited: non-local transport by turbulent amplification

DEFF Research Database (Denmark)

Milovanov, Alexander V.; Rasmussen, Jens Juul

2015-01-01

We revise the applications of self-organized criticality (SOC) as a paradigmatic model for tokamak plasma turbulence. The work, presented here, is built around the idea that some systems do not develop a pure critical state associable with SOC, since their dynamical evolution involves as a compet......We revise the applications of self-organized criticality (SOC) as a paradigmatic model for tokamak plasma turbulence. The work, presented here, is built around the idea that some systems do not develop a pure critical state associable with SOC, since their dynamical evolution involves...... as a competing key factor an inverse cascade of the energy in reciprocal space. Then relaxation of slowly increasing stresses will give rise to intermittent bursts of transport in real space and outstanding transport events beyond the range of applicability of the 'conventional' SOC. Also, we are concerned...... with the causes and origins of non-local transport in magnetized plasma, and show that this type of transport occurs naturally in self-consistent strong turbulence via a complexity coupling to the inverse cascade. We expect these coupling phenomena to occur in the parameter range of strong nonlinearity and time...

Pulsed transport critical currents of Bi2212 tapes in pulsed magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Rogacki, K [Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Wroclaw (Poland); Gilewski, A; Klamut, J [International Laboratory of High Magnetic Fields and Low Temperatures, Polish Academy of Sciences, Wroclaw (Poland); Newson, M; Jones, H [Clarendon Laboratory, University of Oxford, Oxford (United Kingdom); Glowacki, B A [IRC in Superconductivity and Department of Materials Science, University of Cambridge, Cambridge (United Kingdom)

2002-07-01

If high-T{sub C} superconductors are ever to be used in high-field applications, it is vital that the critical surfaces can be mapped under high-field conditions. However, the latest superconductors have high currents even at fields over 20 T, making accurate measurements very difficult due to the thermal and mechanical problems. In this paper, we compare measurements on BSCCO-2212 tape using a number of different methods, particularly an innovative pulsed transport current and pulsed field mode. We show how the analysis of the voltage signal from BSCCO-2212 tape in pulsed conditions may be used to extract the critical current in quasi-stationary conditions. The effect of a metallic substrate on the results is also briefly discussed. (author)

Local air quality management: some evidence of current practices

Energy Technology Data Exchange (ETDEWEB)

Beattie, Clare; Newton, Alex; Longhurst, Jim [University of the West of England, Air Quality Research Group, Bristol (United Kingdom)

1998-12-01

The recent legislative changes, notably the Environment Act 1995 and resultant National Air Quality Strategy have brought new powers and obligations to local authorities to reach specified air quality standards and objectives. Initially this will involve local authorities carrying out a review and assessment of air quality in their locality by December 1999. This paper will outline a project currently being undertaken within the University of the West of England investigating how this legislation is being put into practice and present the results from a nation-wide questionnaire survey of environmental health officers. The study found that local authorities are still at an early stage of the process. It seems probable that one possible barrier to the implementation of Air Quality Management will be communication and cooperation within local authorities. (Author)

Definition of current density in the presence of a non-local potential.

Science.gov (United States)

Li, Changsheng; Wan, Langhui; Wei, Yadong; Wang, Jian

2008-04-16

In the presence of a non-local potential arising from electron-electron interaction, the conventional definition of current density J(c) = (e/2m)([(p-eA)ψ](*)ψ-ψ(*)[(p-eA)ψ]) cannot satisfy the condition of current conservation, i.e., [Formula: see text] in the steady state. In order to solve this problem, we give a new definition of current density including the contribution due to the non-local potential. We show that the current calculated based on the new definition of current density conserves the current and is the same as that obtained from the Landauer-Büttiker formula. Examples are given to demonstrate our results.

Definition of current density in the presence of a non-local potential

International Nuclear Information System (INIS)

Li Changsheng; Wan Langhui; Wei Yadong; Wang Jian

2008-01-01

In the presence of a non-local potential arising from electron-electron interaction, the conventional definition of current density J c = (e/2m)([(p-eA)ψ]*ψ-ψ*[(p-eA)ψ]) cannot satisfy the condition of current conservation, i.e., ∇ . J c ≠ 0 in the steady state. In order to solve this problem, we give a new definition of current density including the contribution due to the non-local potential. We show that the current calculated based on the new definition of current density conserves the current and is the same as that obtained from the Landauer-Buettiker formula. Examples are given to demonstrate our results

Critical excitation spectrum of a quantum chain with a local three-spin coupling.

Science.gov (United States)

McCabe, John F; Wydro, Tomasz

2011-09-01

Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D(4),A(4)) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.

Critical excitation spectrum of a quantum chain with a local three-spin coupling

International Nuclear Information System (INIS)

McCabe, John F.; Wydro, Tomasz

2011-01-01

Using the phenomenological renormalization group (PRG), we evaluate the low-energy excitation spectrum along the critical line of a quantum spin chain having a local interaction between three Ising spins and longitudinal and transverse magnetic fields, i.e., a Turban model. The low-energy excitation spectrum found with the PRG agrees with the spectrum predicted for the (D 4 ,A 4 ) conformal minimal model under a nontrivial correspondence between translations at the critical line and discrete lattice translations. Under this correspondence, the measurements confirm a prediction that the critical line of this quantum spin chain and the critical point of the two-dimensional three-state Potts model are in the same universality class.

Critical current density and wire fabrication of high-TC superconductors

International Nuclear Information System (INIS)

Schlabach, T.D.; Jin, S.; Sherwood, R.C.; Tiefel, T.H.

1989-01-01

In this paper, some of the recent investigations of wire fabrication techniques and critical current behavior in high T c superconductors will be reviewed. In spite of the tremendous interest and research effort, the progress toward major applications of the bulk high-temperature superconductors has been impeded by, among other thins, the low critical currents and their severe deterioration in weak magnetic fields. Significant advances, however, have been made in understanding the causes of the problem as well as in improving the current-carrying capacity through proper microstructural control such as the melt-textured-growth in Y-Ba-Cu-O. The low density of effective flux-pinning sites in bulk Y-Ba-Cu-O limits J c at 77K in high magnetic fields to about 10 4 A/cm 2 even in the absence of weak links. Magnetization measurements on Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O at 77K by various researchers indicate even weaker flux pinning capabilities in these materials than in Y-Ba-Cu-O. The challenge in the future is to obtain suitable flux-pinning defects by choosing the right processing and chemistry changes

The relationship between critical current and microstructure of internal tin wire

International Nuclear Information System (INIS)

Dietderich, D.R.; Hassenzahl, W.V.; Morris, J.W. Jr.

1986-01-01

Prior work on internal tin wire has shown that an increase in critical current results when the Nb 3 Sn reaction temperatures (650-730 0 C) are preceded by low temperature diffusion heat treatments that distribute the tin. These heat treatments produce a more uniform tin distribution through the niobium filament array before substantial Nb 3 Sn formation has occurred. Heat treatments as long as 19 days have been proposed as the optimal heat treatment for the conductor. However, it is possible to substantially reduce the low temperature heat treatment time while retaining the same high critical current. The success of shortened heat treatments may be interpreted on the basis of the Cu-Sn reaction, diffusion kinetics and the Nb 3 Sn growth kinetics

Critical current enhancement by Lorentz force reduction in superconductor-ferromagnet nanocomposites

International Nuclear Information System (INIS)

Blamire, M G; Dinner, R B; Wimbush, S C; MacManus-Driscoll, J L

2009-01-01

Ferromagnetic pinning centres in superconductors form much deeper potential wells than equivalent insulating or metallic non-superconducting inclusions. However, the resultant pinning forces arising from magnetic inclusions are low because the magnetic interaction takes place over the length scale of the magnetic penetration depth which is large in technological superconductors. Nonetheless, we show that a magnetic inclusion can also reduce the Lorentz force on a vortex, yielding a substantially enhanced critical current density for a given pinning force. We calculate this enhancement for a single vortex pinned by a paramagnetic cylinder as well as a vortex lattice interacting with magnetic inclusions, and find that the inclusion of ferromagnetic particles or rods offers a practical means of enhancing the critical currents in oxide high temperature superconductors.

'Leak Current' correction for critical current measurement of no-insulation HTS coil

Energy Technology Data Exchange (ETDEWEB)

Song, Jung Bin [Laboratoire National des Champs Magnétiques Intenses, CNRS, Grenoble (France); Hahn, Seung Yong [Dept. of Electrical and Computer Engineering, Seoul National University, Seoul (Korea, Republic of)

2017-06-15

Discrepancy between a power supply current and an actual “spiral” coil current makes the conventional 4-probe measurement of a critical current (I{sub c}) of a no-insulation (NI) high temperature superconductor (HTS) coil inaccurate and time-consuming. This paper presents a fast and accurate approach for I{sub c} measurement of NI HTS coils. With an NI HTS coil energized at a constant ramping rate, a complete analytic expression for the spiral coil current was obtained from a first-order partial differential equation that derived from an equivalent circuit model of the NI coil. From the analytic solution, both spiral coil current and radial leak current can be obtained simultaneously, which enables fast and accurate measurement of the NI coil I{sub c}. To verify the proposed approach, an NI double-pancake (DP) coil, wound with GdBCO tapes of 6 mm × 0.1 mm, was constructed and its Ic was repeatedly measured with various ramping rates in a bath of liquid nitrogen at 77 K. The measured results agreed well with the calculated ones, which validates the proposed approach to measure I{sub c} of an NI HTS coil.

Stock markets and criticality in the current economic crisis

Science.gov (United States)

da Silva, Roberto; Zembrzuski, Marcelo; Correa, Fabio C.; Lamb, Luis C.

2010-12-01

We show that the current economic crisis has led the market to exhibit a non-critical behavior. We do so by analyzing the quantitative parameters of time series from the main assets of the Brazilian Stock Market BOVESPA. By monitoring global persistence we show a deviation of power law behavior during the crisis in a strong analogy with spin systems (from where this concept was originally conceived). Such behavior is corroborated by an emergent heavy tail of absolute return distribution and also by the magnitude autocorrelation exponent. Comparisons with universal exponents obtained in the international stock markets are also performed. This suggests how a thorough analysis of suitable exponents can bring a possible way of forecasting market crises characterized by non-criticality.

Critical adsorption profiles around a sphere and a cylinder in a fluid at criticality: Local functional theory

Science.gov (United States)

Yabunaka, Shunsuke; Onuki, Akira

2017-09-01

We study universal critical adsorption on a solid sphere and a solid cylinder in a fluid at bulk criticality, where preferential adsorption occurs. We use a local functional theory proposed by Fisher et al. [M. E. Fisher and P. G. de Gennes, C. R. Acad. Sci. Paris Ser. B 287, 207 (1978); M. E. Fisher and H. Au-Yang, Physica A 101, 255 (1980), 10.1016/0378-4371(80)90112-0]. We calculate the mean order parameter profile ψ (r ) , where r is the distance from the sphere center and the cylinder axis, respectively. The resultant differential equation for ψ (r ) is solved exactly around a sphere and numerically around a cylinder. A strong adsorption regime is realized except for very small surface field h1, where the surface order parameter ψ (a ) is determined by h1 and is independent of the radius a . If r considerably exceeds a , ψ (r ) decays as r-(1 +η ) for a sphere and r-(1 +η )/2 for a cylinder in three dimensions, where η is the critical exponent in the order parameter correlation at bulk criticality.

Critical current densities in thick yttrium-barium cuprate (1-2-3) films

International Nuclear Information System (INIS)

Ryvkina, G.G.; Gorlanov, S.F.; Vedernikov, G.E.; Telegin, A.B.; Ryabin, V.A.; Khodos, M.Ya.

1993-01-01

The study of critical current densities j c of oxide superconductors and their thick films is a very important practical task because the value of j c is one of the main criteria for their utilization in modern cryoelectronics. For most devices based on the Josephson effect, the value of j c ∼ 10 2 - 10 3 A/cm 2 is acceptable, which is easily attainable for polycrystalline thick films obtained by stenciling. The study of the current-transport phenomenon involves a number of difficulties, especially for direct current, because both the sample itself and the lead-in contacts are resistance-heated during the measurements, which, in turn, results in lower values of the j c . Measurements with pulsed currents allow one to lower the power that is applied to the sample; the heat that is released in the sample is reduced, in comparison to measurements with direct current, by a factor of the pulsed-current duty cycle. In addition, measurements with direct current detects only the appearance of resistance; it provides no information on the rest of the transition from the normal to the superconductive state, i.e., on the so-called 'tail' of the transition. In this work, the authors studied critical current densities of thick HTSC yttrium-barium cuprate films of the 1-2-3 composition using pulsed current

Analysis of critical current-bend strain relationships in composite Nb3Sn superconducting wires

International Nuclear Information System (INIS)

Luhman, T.; Welch, D.O.

1979-01-01

In order to be used successfully in fusion magnets, Nb 3 Sn conductors must meet several mechanical strain criteria, including tolerance to bending strains encountered during magnet construction. Since Nb 3 Sn is extremely brittle much information has been generated regarding the sensitivity of these conductros to tensile strain. A recent comparison of critical current-bend and tensile test data indicates that the strain required to initiate compound cracking during bending is significantly less than the strain required to do so by tensile of critical current on bending strains in monofilamentary Nb 3 Sn wires is calculated and compared with experimental data. The calculation takes into account a shift in the composite's neutral axis which occurs during bending. The analysis correctly predicts the observed depdndence of the critical current on bending strains

Magnetic response and critical current properties of mesoscopic-size YBCO superconducting samples

International Nuclear Information System (INIS)

Lisboa-Filho, P N; Deimling, C V; Ortiz, W A

2010-01-01

In this contribution superconducting specimens of YBa 2 Cu 3 O 7-δ were synthesized by a modified polymeric precursor method, yielding a ceramic powder with particles of mesoscopic-size. Samples of this powder were then pressed into pellets and sintered under different conditions. The critical current density was analyzed by isothermal AC-susceptibility measurements as a function of the excitation field, as well as with isothermal DC-magnetization runs at different values of the applied field. Relevant features of the magnetic response could be associated to the microstructure of the specimens and, in particular, to the superconducting intra- and intergranular critical current properties.

Magnetic response and critical current properties of mesoscopic-size YBCO superconducting samples

Energy Technology Data Exchange (ETDEWEB)

Lisboa-Filho, P N [UNESP - Universidade Estadual Paulista, Grupo de Materiais Avancados, Departamento de Fisica, Bauru (Brazil); Deimling, C V; Ortiz, W A, E-mail: plisboa@fc.unesp.b [Grupo de Supercondutividade e Magnetismo, Departamento de Fisica, Universidade Federal de Sao Carlos, Sao Carlos (Brazil)

2010-01-15

In this contribution superconducting specimens of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} were synthesized by a modified polymeric precursor method, yielding a ceramic powder with particles of mesoscopic-size. Samples of this powder were then pressed into pellets and sintered under different conditions. The critical current density was analyzed by isothermal AC-susceptibility measurements as a function of the excitation field, as well as with isothermal DC-magnetization runs at different values of the applied field. Relevant features of the magnetic response could be associated to the microstructure of the specimens and, in particular, to the superconducting intra- and intergranular critical current properties.

Structural and critical current properties in Al-doped MgB2

International Nuclear Information System (INIS)

Zheng, D.N.; Xiang, J.Y.; Lang, P.L.; Li, J.Q.; Che, G.C.; Zhao, Z.W.; Wen, H.H.; Tian, H.Y.; Ni, Y.M.; Zhao, Z.X.

2004-01-01

A series of Al-doped Mg 1-x Al x B 2 samples have been fabricated and systematic study on structure and superconducting properties have been carried out for the samples. In addition to a structural transition observed by XRD, TEM micrographs showed the existence of a superstructure of double c-axis lattice constant along the direction perpendicular to the boron honeycomb sheet. In order to investigate the effect of Al doping on flux pinning and critical current properties in MgB 2 , measurements on the superconducting transition temperature T c , irreversible field B irr and critical current density J c were performed too, for the samples with the doping levels lower than 0.15 in particular. These experimental observations were discussed in terms of Al doping induced changes in carrier concentration

Structural and critical current properties in Al-doped MgB 2

Science.gov (United States)

Zheng, D. N.; Xiang, J. Y.; Lang, P. L.; Li, J. Q.; Che, G. C.; Zhao, Z. W.; Wen, H. H.; Tian, H. Y.; Ni, Y. M.; Zhao, Z. X.

2004-08-01

A series of Al-doped Mg 1- xAl xB 2 samples have been fabricated and systematic study on structure and superconducting properties have been carried out for the samples. In addition to a structural transition observed by XRD, TEM micrographs showed the existence of a superstructure of double c-axis lattice constant along the direction perpendicular to the boron honeycomb sheet. In order to investigate the effect of Al doping on flux pinning and critical current properties in MgB 2, measurements on the superconducting transition temperature Tc, irreversible field Birr and critical current density Jc were performed too, for the samples with the doping levels lower than 0.15 in particular. These experimental observations were discussed in terms of Al doping induced changes in carrier concentration.

Current algebra of WZNW models at and away from criticality

International Nuclear Information System (INIS)

Abdalla, E.; Forger, M.

1992-01-01

In this paper, the authors derive the current algebra of principal chiral models with a Wess-Zumino term. At the critical coupling where the model becomes conformally invariant (Wess-Zumino-Novikov-Witten theory), this algebra reduces to two commuting Kac-Moody algebras, while in the limit where the coupling constant is taken to zero (ordinary chiral model), we recover the current algebra of that model. In this way, the latter is explicitly realized as a deformation of the former, with the coupling constant as the deformation parameter

Low field critical currents and ac losses of thin film niobium--tin superconductors

International Nuclear Information System (INIS)

Howard, R.E.

1977-01-01

The results of a study of the low field critical current and ac loss properties of niobium-tin thin films and layered composites fabricated by electron-beam coevaporation are presented. Particular emphasis is placed upon determining the suitability of this material for use as a conductor in a superconducting power transmission line. Chapter I contains a summary of this work and its major results together with an introduction to the scientific and engineering concepts associated with a superconducting power transmission line. Chapter II is a discussion of the physics of current transport and the associated loss mechanisms in a type-II superconductor. Chapter III gives the details of the electron-beam coevaporation technique developed to fabricate the samples for this study. Also discussed in this chapter are the effects of the evaporation conditions on the growth morphology of the niobium-tin films. Chapter IV presents the details of the experimental techniques developed to measure the ac loss and critical current in these samples as a function of temperature. Chapter V shows the dependence of the critical current of these films and composites on temperature, magnetic field, and on the number of artificially introduced pinning centers in the layered composites. Experimental results are also presented concerning the stability of these conductors against flux jumps. Chapter VI is a discussion of the ac losses in these samples. Detailed comparisons are made between the measured loss and the predictions of the critical state model

Thermal domains in inhomogeneous current-carrying superconductors. Current-voltage characteriscs and dynamics of domain formation after current jumps

International Nuclear Information System (INIS)

Bezuglyj, A.I.; Shklovskij, V.A.

1984-01-01

The static and dynamic behavior of thermal domains in inhomogeneous superconducting films, where the inhomogeneity behaves like a portion of the film with a reduced critical current, have been studied theoretically within the framework of the phenomenological approach, using the heat balance equation and the dependence of the superconductor critical current on temperature. Depending on the size of the inhomogeneity (local or extended) and on the relative values of parameters of the homogeneous and inhomogeneous regions, different types of current-voltage characteristics are obtained. The nonstationary problem of thermal domain formation near the inhomogeneity after a current jump has been solved, and the domain boundary (kink) dynamics at a distance from the inhomogeneity has been analyzed. A combination of the results allows one to describe the whole process of normal phase formation and its spread throughout the superconducting film

The influence of strain introduced by differential thermal contraction on the critical current of Nb3Sn supercontractors

International Nuclear Information System (INIS)

Pasztor, G.; Jakob, B.

1992-01-01

The NET Team initiated in 1988 a development program for a high current cable-in-conduit superconductor planned for fusion magnets. The basic strand chosen for the cable was a Nb 3 Sn wire of TWCA made by the MJR method. The electrical testing of the stand and sub-cables was carried out at several European Laboratories including PSI (Paul Scherrer Institute). The inter-laboratory comparison of the results revealed large differences in the measured critical currents of the strands. Obviously, each laboratory performed the measurement of critical current in its own way, and as a result some discrepancies in the measured values were inevitable. No standard technique of measuring critical current has been developed for Nb 3 Sn wires. The main source of difficulty arises from the strain sensitivity of Nb 3 Sn. It has been shown that the sample holder material and geometry as well as the bonding method of the specimen to its holder have important effects on the critical current measurements. It was found recently that the reaction mandrel material significantly influences the current-carrying capacity of Nb 3 Sn wires. The aim of this paper is to improve current understanding of the effect of sample configuration on critical current in Nb 3 Sn multifilamentary wires. The present study confirms the important role of reaction mandrel material on critical current. Based on comparative critical current measurements of straight and coil samples, an attempt is made to find the sample configuration which eliminates the strain induced in the specimen

Thermal instability and current-voltage scaling in superconducting fault current limiters

Energy Technology Data Exchange (ETDEWEB)

Zeimetz, B [Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB1 3QZ (United Kingdom); Tadinada, K [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Eves, D E [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Coombs, T A [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom); Evetts, J E [Department of Materials Science and Metallurgy, Cambridge University, Pembroke Street, Cambridge CB1 3QZ (United Kingdom); Campbell, A M [Department of Engineering, Cambridge University, Trumpington Road, Cambridge CB2 1PZ (United Kingdom)

2004-04-01

We have developed a computer model for the simulation of resistive superconducting fault current limiters in three dimensions. The program calculates the electromagnetic and thermal response of a superconductor to a time-dependent overload voltage, with different possible cooling conditions for the surfaces, and locally variable superconducting and thermal properties. We find that the cryogen boil-off parameters critically influence the stability of a limiter. The recovery time after a fault increases strongly with thickness. Above a critical thickness, the temperature is unstable even for a small applied AC voltage. The maximum voltage and maximum current during a short fault are correlated by a simple exponential law.

Calculation of persistent currents in superconducting magnets

Directory of Open Access Journals (Sweden)

C. Völlinger

2000-12-01

Full Text Available This paper describes a semianalytical hysteresis model for hard superconductors. The model is based on the critical state model considering the dependency of the critical current density on the varying local field in the superconducting filaments. By combining this hysteresis model with numerical field computation methods, it is possible to calculate the persistent current multipole errors in the magnet taking local saturation effects in the magnetic iron parts into consideration. As an application of the method, the use of soft magnetic iron sheets (coil protection sheets mounted between the coils and the collars for partial compensation of the multipole errors during the ramping of the magnets is investigated.

Phonon-induced enhancements of the energy gap and critical current in superconducting aluminum

International Nuclear Information System (INIS)

Seligson, D.

1983-05-01

8 to 10 GHz phonons were generated by piezoelectric transduction of a microwave and by means of a quartz delay line, were allowed to enter the aluminum only after the microwaves had long since disappeared. The maximum enhancements detected were [deltaT/T/sub c/] = -0.07, for i/sub c/ and [deltaT/T/sub c/] = -0.03 for Δ. The power- and temperature-dependence (0.82 less than or equal to T/T/sub c/ less than or equal to 0.994) of the enhancements were compared with the prediction of a theory given by Eliashberg. The gap-enhancement was in good agreement with the theory only for low input lower. The critical current measurements are predicted to be in rough agreement with the Δ measurements but this was not observed. The magnitude of the critical current enhancements was typically more than twice the observed gap enhancements. The measured critical current enhancement was relatively independent of temperature whereas the gap enhancement decreased rapidly as the temperature was lowered

Enhancement of critical currents in superconducting cylindrical samples by circular magnetization

Energy Technology Data Exchange (ETDEWEB)

Sikora, A; Makiej, B

1986-07-16

Evidence is presented for an enhancement of the critical current by a circular magnetization in cylindrical samples of superconductors such as Sn, In, and In-Pb alloy containing 20 wt% ferromagnetic carbon steel particles. The mechanism of this phenomenon is explained.

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors.

Science.gov (United States)

Goodrich, L F; Cheggour, N; Stauffer, T C; Filla, B J; Lu, X F

2013-01-01

We review variable-temperature, transport critical-current (I c) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium ("liquid" or I c liq) at 5

Critical current fluctuation in a microwave-driven Josephson junction

International Nuclear Information System (INIS)

Dong Ning; Sun Guozhu; Wang Yiwen; Cao Junyu; Yu Yang; Chen Jian; Kang Lin; Xu Weiwei; Han Siyuan; Wu Peiheng

2007-01-01

Josephson junction devices are good candidates for quantum computation. A large energy splitting was observed in the spectroscopy of a superconducting Josephson junction. The presence of the critical current fluctuation near the energy splitting indicated coupling between the junction and a two-level system. Furthermore, we find that this fluctuation is microwave dependent. It only appears at certain microwave frequency. This relation suggested that the decoherence of qubits is influenced by the necessary computing operations

Calculation of the Critical Current Reduction in a Brittle Round Multifilamentary Wire due to External Forces

NARCIS (Netherlands)

ten Haken, Bernard; Godeke, A.; ten Kate, Herman H.J.

1994-01-01

A simple model is presented that can describe the electro-mechanical state of a multifilamentary wire. An elastic cylinder model is used to derive the strain state analytically. Axial and transverse forces came a position dependent critical current density in the wire. The integral critical current

Thermodynamic parameters of single- or multi-band superconductors derived from self-field critical currents

Energy Technology Data Exchange (ETDEWEB)

Talantsev, Evgueni [Robinson Research Institute, Victoria University of Wellington, Lower Hutt (New Zealand); Crump, Wayne P.; Tallon, Jeffery L. [Robinson Research Institute, Victoria University of Wellington, Lower Hutt (New Zealand); MacDiarmid Institute for Advanced Materials and Nanotechnology, Lower Hutt (New Zealand)

2017-12-15

Key questions for any superconductor include: what is its maximum dissipation-free electrical current (its 'critical current') and can this be used to extract fundamental thermodynamic parameters? Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self-field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here, using an extended BCS-like model, we calculate the penetration depth from the temperature dependence of the superconducting energy gap thus allowing us to fit self-field critical current data. In this way we extract from the T-dependent gap a set of key thermodynamic parameters, the ground-state penetration depth, energy gap and jump in electronic specific heat. Our fits to 79 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent and the extracted parameters agree well with reported bulk values. Samples include thin films, wires or nanowires of single- or multi-band s-wave and d-wave superconductors of either type I or type II. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Three-Dimensional Non-Fermi-Liquid Behavior from One-Dimensional Quantum Critical Local Moments

Science.gov (United States)

Classen, Laura; Zaliznyak, Igor; Tsvelik, Alexei M.

2018-04-01

We study the temperature dependence of the electrical resistivity in a system composed of critical spin chains interacting with three-dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2 Pt2 Pb , a metal where itinerant electrons coexist with localized moments of Yb ions which can be described in terms of effective S =1 /2 spins with a dominantly one-dimensional exchange interaction. The spin subsystem becomes critical in a relatively weak magnetic field, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the spin criticality by calculating the electronic relaxation rate and the dc resistivity and establish its quasilinear temperature dependence.

Critical current degradation in superconducting niobium-titanium alloys in external magnetic fields under loading

International Nuclear Information System (INIS)

Bojko, V.S.; Lazareva, M.B.; Starodubov, Ya.D.; Chernyj, O.V.; Gorbatenko, V.M.

1992-01-01

The effect of external magnetic fields on the stress at which the critical current starts to degrade (the degradation threshold σ 0 e ) under mechanical loads in superconducting Nb-Ti alloys is studied and a possible mechanism of realization of the effect observed is proposed.It is assumed that additional stresses on the transformation dislocation from the external magnetic fields are beneficial for the growth of martensite inclusions whose superconducting parameters (critical current density j k and critical temperature T k ) are lower then those in the initial material.The degradation threshold is studied experimentally in external magnetic fields H up to 7 T.The linear dependence σ 0 e (H) is observed.It is shown that external magnetic fields play an important role in the critical current degradation at the starting stages of deformation.This fact supports the assumption that the degradation of superconducting parameters under loading are due to the phenomenon of superelasticity,i.e. a reversible load-induced change in the martensite inclusions sizes rather than the reversible mechanical twinning.The results obtained are thought to be important to estimating superconducting solenoid stability in a wide range of magnetic fields

Stress effect on the critical current of Ti-Nb-Zr-Ta multifilamentary superconductors

International Nuclear Information System (INIS)

Monju, Yoshiyuki; Tatara, Isamu

1978-01-01

The tensile behaviour at R.T., 77K, 4.2K and the degradation of the critical current with stress have been measured on multifilamentary Ti-Nb-Zr-Ta alloy superconductors. The assembly of the stress effect apparatus is as follows; At the center of the 60KOe superconducting solenoid coil, sample wire is hold around an FRP spool and the wire ends are gripped to the load train. Current is supplied through helium vapourcooled flexible leads up to 2000 A. It was clear that a definite degradation of the critical current with stress was not observed up to the stress equal to one third of the fracture stress at 4.2K. This stress value should be defined the maximum allowable stress of alloy superconductors examined from stress effects. (author)

Microstructure and critical current of superconducting YBa/sub 2/Cu/sub 3/Osub(7-x)

Energy Technology Data Exchange (ETDEWEB)

Camps, R A; Evetts, J E; Glowacki, B A; Newcomb, S B; Somekh, R E; Stobbs, W M

1987-09-17

The authors present the main results of a detailed electron microscopical study of sintered YBa/sub 2/Cu/sub 3/0sub(7-x), and discuss their relevance to observed critical current and its modification by increased silicon impurity levels. In the light of these results, the prospects are assessed for controlling microstructure development so as to optimize the critical current for technological application.

Grain size dependence of the critical current density in YBa2Cu3Ox superconductors

International Nuclear Information System (INIS)

Kuwabara, M.; Shimooka, H.

1989-01-01

The grain size dependence of the critical current density in bulk single-phase YBa 2 Cu 3 O x ceramics was investigated. The grain size of the materials was changed to range approximately from 1.0 to 25 μm by changing the conditions of power processing and sintering, associated with an increase in the sintered density of the materials with increasing grain size. The critical current density has been found to exhibit a significant grain size dependence, changing from 880 A/cm 2 to a value of 100 A/cm 2 with a small increase in the average grain size from 1.2 to 2.0 μm. This seems to provide information about the nature of the weak link between superconducting grains which might govern the critical current density of the materials

The nature of transport critical current hysteresis in HTSC: magnetic fields and high pressures. [Y-Ba-Cu-O

Energy Technology Data Exchange (ETDEWEB)

Svistunov, V M; Yachenko, A.I. d' ; Tarenkov, V Yu [Donetsk Physico-Technical Inst., Ukrainian SSR (USSR)

1991-12-01

It was found that pressure has a strong influence on the critical current hysteresis loop of ceramics at H {proportional to} 10 kOe. The phenomenon is attributed to the critical current hysteresis of separate Josephson contacts and is due to the Abrikosov vortex density gradient within granules. The gradient defines both the sign and the value of the pinning current, whereas the sign of Meissner reversible surfaces current component is determined by the external field H direction. As a result the critical current of Josephson contacts defined by the total surface value depends on the magnetic prehistory of a sample. (orig.).

Nb/sub 3/Sn critical-current measurements using tubular fiberglass-epoxy mandrels

International Nuclear Information System (INIS)

Goodrich, L.F.; Bray, S.L.; Stauffer, T.C.

1989-01-01

A systematic study of the effect of sample mounting techniques on the superconducting critical-current measurement was made in conjunction with the VAMAS (Versailles Agreement on Advanced Materials and Standards) interlaboratory comparison (round robin) measurements. A seemingly small change in mandrel geometry can result in a 40% change in the measured critical current of a Nb/sub 3/Sn sample at 12 T. This is a result of a change in the conductor pre-strain at 4 K caused by variation in thermal contraction between thick- and thin-walled fiberglass-epoxy composite (G-10) tubes. An approximate measure of the variations in thermal contraction (from room to liquid nitrogen temperature) indicate a 0.2% greater contraction for the thick-walled tube. This difference, combined with strain sensitivity measurements, is consistent with the observed decrease in critical current. Previous publications on thermal contraction of G-10 have addressed the plate geometry, but not the tube geometry. The contraction of a G-10 plate is highly anisotropic. The radial contraction of a tube is different than the contraction of a plate, however, because the circumferential fiberglass is put into hoop compression by the epoxy, and the resulting contraction is a competition between the two structural components. This appears to be the source of the variation in thermal contraction with tube wall thickness

Order parameter effect critical fields and current of Y1–xPrx:123 superconductors

Directory of Open Access Journals (Sweden)

Sedky A.

2018-03-01

Full Text Available Fluctuation induced conductivity by Pr substitution at Y sites of Y1-xPrx:123 superconductors is reported. It is found that the mean field temperature Tcmf, deduced from the peak of dρ/dT versus T plot, gradually decreases by increasing Pr up to 0.40. The order parameter dimensionality (OPD is estimated from the slope of the logarithmic plot between excess conductivity Δσ and reduced temperature є. Interestingly, the crossover from 2D to 3D is obtained for samples with Pr = 0.00, 0.10 and 0.20, while with increasing Pr up to 0.40, the crossover from 0D to quasi-2D is obtained. On the other hand, the calculated values of interlayer coupling, coherence lengths, critical fields and critical current decrease with increasing Pr up to 0.20, but with the further increase of Pr, up to 0.40, they increase. The hole carriers/Cu ions anisotropy and G-L parameter gradually increase with Pr up to 0.40. Our results are discussed in terms of the effects of Pr substitution at Y site, such as oxygen rearrangements, anisotropy, hybridization and localization of holes in the overdoped region.

Localization of the phantom force induced by the tunneling current

Science.gov (United States)

Wutscher, Thorsten; Weymouth, Alfred J.; Giessibl, Franz J.

2012-05-01

The phantom force is an apparently repulsive force, which can dominate the atomic contrast of an AFM image when a tunneling current is present. We described this effect with a simple resistive model, in which the tunneling current causes a voltage drop at the sample area underneath the probe tip. Because tunneling is a highly local process, the areal current density is quite high, which leads to an appreciable local voltage drop that in turn changes the electrostatic attraction between tip and sample. However, Si(111)-7×7 has a metallic surface state and it might be proposed that electrons should instead propagate along the surface state, as through a thin metal film on a semiconducting surface, before propagating into the bulk. In this paper, we first measure the phantom force on a sample that displays a metallic surface state [here, Si(111)-7×7] using tips with various radii. If the metallic surface state would lead to a constant electrostatic potential on the surface, we would expect a direct dependence of the phantom force with tip radius. In a second set of experiments, we study H/Si(100), a surface that does not have a metallic surface state. We conclude that a metallic surface state does not suppress the phantom force, but that the local resistance Rs has a strong effect on the magnitude of the phantom force.

Tensile damage and its influence on the critical current of Bi2223/Ag superconducting composite tape

International Nuclear Information System (INIS)

Ochiai, S; Nagai, T; Okuda, H; Oh, S S; Hojo, M; Tanaka, M; Sugano, M; Osamura, K

2003-01-01

We have studied the tensile behaviour of Bi2223 superconducting composite tapes at room temperature, and the influence of the tensile damages introduced at room temperature on the critical current I c and the n values at 77 K. In the measurement of the I c and n values, the overall composite with a gauge length 60 mm was divided into six elements with a gauge length of 10 mm in order to find the correlation of the I c and n values of the overall composite to those of the local elements which constitute the composite. From the measured stress-strain curve of the composite and the calculated residual strain of the Bi2223 filaments, the intrinsic fracture strain of Bi2223 filaments was estimated to be 0.09-0.12%. When the applied strain was lower than the onset strain of the filament damage, the original I c and n values were retained both in the overall composite and the elements. In this situation, while the overall voltage at the transition from superconductivity to normal conductivity of the composite was the sum of the voltages of the constituent elements, among all elements the overall voltage was affected more by the element with the lower I c (higher voltage). The damage of the filaments arose first locally, resulting in a reduction of the I c and n values in the corresponding local element, even though the other elements retained the original I c and n values. In this situation, the voltage of the overall composite stemmed dominantly from that of the firstly damaged weakest element, and the overall I c and n values were almost determined by the values of such an element. After the local element was fully damaged, the damage arose also in other elements, resulting in segmentation of the filaments. Thus, the I c and n values were reduced in all elements. The correlation of I c between the overall composite and the elements could be described comprehensively for non-damaged and damaged states from the voltage-current relation

Prospects for enhancement of critical current of HTSC: thin films with artificial pinning centres

Energy Technology Data Exchange (ETDEWEB)

Mozhaev, P.B. (Institute of Physics and Technology RAS, Moscow (Russian Federation)); Mozhaev, J.E.; Khoryushin, A.V.; Bindslev Hansen, J.; Jacobsen, C.S. (Technical Univ. of Denmark, Dept. of Physics, Kgs. Lyngby (Denmark)); Kotelyanskil, I.M.; Luzanov, V.A. (Institute of Radio Engineering and Electronics RAS, Moscow (Russian Federation)); Puriy, A.V. (Moscow Institute of Physics and Technology, Moscow (Russian Federation)); Yurchenko, V.; Johansen, T. (Univ. of Oslo, Dept. of Physics, Oslo (Norway))

2008-10-15

Improvement of the critical current of YBCO thin films and heterostructures remains one of the main tasks for fabrication of modern superconducting wires and connectors. Possible ways of achieving the goal are choice of superconductor composition, engineering of artificial pinning centres, and combination of the superconducting layer with other materials. The team of the Department of Physics at Technical University of Denmark is working in all these fields and this paper is a short review of our achievements in an attempt to improve the critical current density of YBCO thin films. (au)

Non-local currents in 2D QFT: an alternative To - the quantum inverse scattering method

International Nuclear Information System (INIS)

Bernard, D.; Leclair, A.; Cornell Univ., Ithaca, NY

1990-01-01

The formalism based on non-local charges that we propose provides an alternative to the quantum inverse scattering method for solving integrable quantum field theories in 2D. The content of the paper is: 1. Introduction: historical background. 2. The NLC approach to 2D QFT: a summary. 3 Exchange algebras and on-shell conservation laws: why non-local charges are useful. 4. The lattice construction: the geometrical origin of non-local conserved currents. 5. The continuum construction: how to deal with non-local conserved currents. 6. Examples: Yangian and quantum group currents. 7 Conclusions: open problems. 22 refs., 4 figs

Disaster management and the critical thinking skills of local emergency managers: correlations with age, gender, education, and years in occupation.

Science.gov (United States)

Peerbolte, Stacy L; Collins, Matthew Lloyd

2013-01-01

Emergency managers must be able to think critically in order to identify and anticipate situations, solve problems, make judgements and decisions effectively and efficiently, and assume and manage risk. Heretofore, a critical thinking skills assessment of local emergency managers had yet to be conducted that tested for correlations among age, gender, education, and years in occupation. An exploratory descriptive research design, using the Watson-Glaser Critical Thinking Appraisal-Short Form (WGCTA-S), was employed to determine the extent to which a sample of 54 local emergency managers demonstrated the critical thinking skills associated with the ability to assume and manage risk as compared to the critical thinking scores of a group of 4,790 peer-level managers drawn from an archival WGCTA-S database. This exploratory design suggests that the local emergency managers, surveyed in this study, had lower WGCTA-S critical thinking scores than their equivalents in the archival database with the exception of those in the high education and high experience group. © 2013 The Author(s). Journal compilation © Overseas Development Institute, 2013.

Tensile Strain Dependence of Critical Current for RHQ-Nb3Al Wires

OpenAIRE

Jin, Xinzhe; Oguro, Hidetoshi; Nakamoto, Tatsushi; Awaji, Satoshi; Ogitsu, Toru; Tsuchiya, Kiyosumi; Yamamoto, Akira; Kikuchi, Akihiro; Takeuchi, Takao

2011-01-01

KEK and NIMS have been jointly developing Nb3Al superconducting wire with a rapid heating and quenching (RHQ) method towards high field accelerator magnets in the Large Hadron Collider (LHC) luminosity upgrade. A15-type superconductors such as Nb3Al and Nb3Sn exhibit strain dependence with respect to their critical currents. Therefore, a thorough understanding of strain behavior is necessary for high field accelerator magnet development, which will be critical for the luminosity upgrade of th...

Transport critical current density in flux creep model

International Nuclear Information System (INIS)

Wang, J.; Taylor, K.N.R.; Russell, G.J.; Yue, Y.

1992-01-01

The magnetic flux creep model has been used to derive the temperature dependence of the critical current density in high temperature superconductors. The generally positive curvature of the J c -T diagram is predicted in terms of two interdependent dimensionless fitting parameters. In this paper, the results are compared with both SIS and SNS junction models of these granular materials, neither of which provides a satisfactory prediction of the experimental data. A hybrid model combining the flux creep and SNS mechanisms is shown to be able to account for the linear regions of the J c -T behavior which are observed in some materials

Contactless estimation of critical current density and its temperature dependence using magnetic measurements

Czech Academy of Sciences Publication Activity Database

Youssef, A.; Baničová, L.; Švindrych, Zdeněk; Janů, Zdeněk

2010-01-01

Roč. 118, č. 5 (2010), s. 1036-1037 ISSN 0587-4246. [Czech and Slovak Conference on Magnetism /14./. Košice, 06.07.2010-09.07.2010] R&D Projects: GA MŠk(CZ) ME10069 Institutional research plan: CEZ:AV0Z10100520 Keywords : superconductivity * critical state * Bean model * critical current density Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.467, year: 2010

Contradiction between the results of observations of resistance and critical current quantum oscillations in asymmetric superconducting rings

International Nuclear Information System (INIS)

Gurtovoi, V. L.; Dubonos, S. V.; Karpii, S. V.; Nikulov, A. V.; Tulin, V. A.

2007-01-01

Magnetic field dependences of critical current, resistance, and rectified voltage of asymmetric (half circles of different widths) and symmetrical (half circles of equal widths) aluminum rings close to the super-conducting transition were measured. All these dependences are periodic magnetic field functions with periods corresponding to the flux quantum in the ring. The periodic dependences of critical current measured in opposite directions were found to be close to each other for symmetrical rings and shifted with respect to each other by half the flux quantum in asymmetric rings with ratios between half circle widths of from 1.25 to 2. This shift of the dependences by a quarter of the flux quantum as the ring becomes asymmetric makes critical current anisotropic, which explains the effect of alternating current rectification observed for asymmetric rings. Shifts of the extrema of the periodic dependences of critical current by a quarter of the flux quantum directly contradict the results obtained by measuring asymmetric ring resistance oscillations, whose extrema are, as for symmetrical rings, observed at magnetic fluxes equal to an integer and a half of flux quanta

Optimum launching of electron-cyclotron power for localized current drive in a hot tokamak

International Nuclear Information System (INIS)

Smith, G.R.

1989-05-01

Optimum launch parameters are determined for localized electron-cyclotron current drive near the magnetic axis and the q=2 surface by solving several minimization problems. For central current drive, equatorial and bottom launch are compared. Localized current drive near q=2 is studied for equatorial launch and for an alternative outside launch geometry that may be better for suppressing tearing modes and controlling disruptions. 6 refs., 2 figs

Reversible oxidation and critical current of YBa2Cu3Ox coated conductors

International Nuclear Information System (INIS)

Claus, H.; Uprety, K.K.; Ma, B.; Paulikas, A.P.; Vlasko-Vlasov, V.K.; Welp, U.; Veal, B.W.; Gray, K.E.

2004-01-01

We were able to vary the oxygen concentration of a YBCO coated-conductor sample from the under-doped to the over-doped regime. This was achieved by secondary oxygenation treatments at temperatures between 250 deg. C and 500 deg. C employing a novel oxygenation scheme. The YBCO-coated conductor was fabricated by the inclined substrate deposition method. Superconducting transition temperature and critical current as function of temperature and magnetic field were determined by a contact-free magnetization technique on a ring sample. It is observed that for temperatures at and below 77 K, the maximum critical current is obtained in the most over-doped state where the transition temperature is significantly depressed

Correlations between critical current density, jc, critical temperature, Tc, and structural quality of Y1B2Cu3O7-x thin superconducting films

International Nuclear Information System (INIS)

Chrzanowski, J.; Xing, W.B.; Atlan, D.

1994-01-01

Correlations between critical current density (j c ) critical temperature (T c ) and the density of edge dislocations and nonuniform strain have been observed in YBCO thin films deposited by pulsed laser ablation on (001) LaAlO 3 single crystals. Distinct maxima in j c as a function of the linewidths of the (00 ell) Bragg reflections and as a function of the mosaic spread have been found in the epitaxial films. These maxima in j c indicate that the magnetic flux lines, in films of structural quality approaching that of single crystals, are insufficiently pinned which results in a decreased critical current density. T c increased monotonically with improving crystalline quality and approached a value characteristic of a pure single crystal. A strong correlation between j c and the density of edge dislocations N D was found. At the maximum of the critical current density the density of edge dislocations was estimated to be N D ∼1-2 x 10 9 /cm 2

Analysis of critical thinking ability in direct current electrical problems solving

Science.gov (United States)

Hartono; Sunarno, Widha; Sarwanto; Arya Nugraha, Dewanta

2017-11-01

This study concern on analyzing the ability of students in critical thinking skills on the subject matter of direct current electricity. Samples were taken using purposive random sampling consisted of 32 students of grade XI, Multimedia 1, SMK Negeri 3 Surakarta in academic year 2016/2017. This study used descriptive quantitative method. The data were collected using tests and interviews regarding the subject matter of direct current electricity. Based on the results, students are getting some difficulties in solving problem in indicator 4. The average of students’ correct answer is 62.8%.

Coexistence in neutral theories: interplay of criticality and mild local preferences

International Nuclear Information System (INIS)

Borile, Claudio; Molina-Garcia, Daniel; Muñoz, Miguel A; Maritan, Amos

2015-01-01

Neutral theories have played a crucial and revolutionary role in fields such as population genetics and biogeography. These theories are critical by definition, in the sense that the overall growth rate of each single allele/species/type vanishes. Thus each species in a neutral model sits at the edge between invasion and extinction, allowing for the coexistence of symmetric/neutral types. However, in finite systems, mono-dominated states are ineluctably reached in relatively short times owing to demographic fluctuations, thus leaving us with an unsatisfactory framework to rationalize empirically-observed long-term coexistence. Here, we scrutinize the effect of heterogeneity in quasi-neutral theories, in which there can be a local mild preference for some of the competing species at some sites, even if the overall species symmetry is maintained. As we show here, mild biases at a small fraction of locations suffice to induce overall robust and durable species coexistence, even in regions arbitrarily far apart from the biased locations. This result stems from the long-range nature of the underlying critical bulk dynamics and has a number of implications, for example, in conservation ecology as it suggests that constructing local specific ‘sanctuaries’ for different competing species can result in global enhancement of biodiversity, even in regions arbitrarily distant from the protected refuges. (paper)

Flux pinning and critical current in layered type-II superconductors in parallel magnetic fields

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We have shown, within the Ginzburg-Landau theory, that the interaction between vortices and normal-metal layers in high-T c superconductor--normal-metal superlattices can cause high critical-current densities j c . The interaction is primarily magnetic, except at very low temperatures T, where the core interaction is dominant. For a lattice of vortices commensurate with an array of normal-metal layers in a parallel magnetic field H, strong magnetic pinning is obtained, with a nonmonotonic critical-current dependence on H, and with j c of the order of 10 7 --10 8 A/cm 2

Critical current densities and vortex dynamics in FeTexSe1-x single crystals

International Nuclear Information System (INIS)

Taen, T.; Tsuchiya, Y.; Nakajima, Y.; Tamegai, T.

2010-01-01

The critical current density and the normalized relaxation rate are reported in FeTe 0.59 Se 0.41 single crystal. Critical current density is of order of 10 5 A/cm 2 , which is comparable to that in Co-doped BaFe 2 As 2 . In low temperature and low field region, the vortex dynamics of this system is well defined by the collective creep theory, which is quite similar to Co-doped BaFe 2 As 2 reported before. We also discuss the origin of the anomaly in the field dependence of the relaxation rate.

Development of MgB2 superconductor wire with high critical current

International Nuclear Information System (INIS)

Kim, Chan Joong; Jun, Byung Hyuk; Park, Soon Dong; Kim, Nam Kyu; Kim, Yi Jeong; Yi, Ji Hye; Lee, Ji Hyun; Tan, Kai Sin

2009-07-01

The MgB 2 superconductor with smaller grain size could improve its critical properties by providing flux pinning centers with high grain boundary density. The effects of C doping such as charcoal, paper ash and glycerin on the superconducting properties was investigated for in situ processed MgB 2 samples using low purity semi-crystalline B powder. The results show a decrease in Tc and an enhancement of Jc at high fields for the C-doped samples as compared to the un-doped samples. A combined process of a mechanical ball milling and liquid glycerin (C 3 H 8 O 3 ) treatment of B powder has been conducted to enhance the superconducting properties of MgB 2 . The mechanical ball milling was effective for grain refinement, and a lattice disorder was easily achieved by glycerin addition. With the combined process, the critical properties was further increased due to a higher grain boundary density and a greater C substitution. To get fine grain structure of MgB 2 with high critical current properties, mechanical milling for as-received B powder and low temperature solid-state reaction of 550 or 600 .deg. C were attempted to in situ powder-in-tube processed MgB 2 /Fe wires. The critical current properties of the MgB 2 wires using the milled B powder were enhanced due to a smaller grain size and an increased volume of the superconducting phase. The solid-state reaction of a low temperature process for the samples using the milled B powder resulted in a poorer crystallinity with a smaller grain size, which improved superconducting properties. We established the system to measure the transport current properties of the MgB 2 wires. The field dependence of the transport Jc was evaluated for the MgB 2 wires heat-treated at different heat treatment conditions using ball-milled and glycerin-treated B powder. The MgB 2 magnet was developed and the AC loss of MgB 2 wire was also investigated. A conduction cooling device to cool the MgB 2 coil down to 4 K has been fabricated and the

Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

International Nuclear Information System (INIS)

Zhu, Yunpeng; Wang, Gang; Liu, Liyuan; Yang, Xinsheng; Zhao, Yong

2015-01-01

Abstract : HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate. - Highlight: • A continuous Hall sensor array system has been designed. • The inhomogeneity of YBCO tape with ferromagnetic substrate can be detected by HAS. • Finite element method is an effective method for calibrating the remanent field.

Numerical versus analytical Ic(H) patterns in Josephson junctions with periodically alternating critical current density

International Nuclear Information System (INIS)

Lazarides, N

2004-01-01

An analytical expression for the magnetic-field-dependent critical current I c (H) of Josephson junctions with periodically alternating critical current density J c (x) is derived within the uniform field approximation. Comparison with numerically calculated I c (H) patterns for junctions with identical, thick, periodically arranged defects with the corresponding analytical expression reveals fair agreement for a wide range of parameters, due to increased characteristic length. Based on qualitative arguments, we give the dependence of the new characteristic length on the geometrical parameters of the junction, which is in agreement with self-consistent calculations with the static sine-Gordon equation. The analytical expression captures the observed qualitative features of the I c (H) patterns, while it is practically exact for short junctions or high fields. It also produces the shift of the major peak from the zero-field position of the standard Fraunhofer pattern to another position related to the periodicity of the critical current density in φ-junctions

Investigation on the enhancement of the critical current densities in bronze-process Nb3Sn

International Nuclear Information System (INIS)

Hong, M.; Wu, I.W.; Morris, J.W. Jr.; Gilbert, W.; Hassenzahl, W.V.; Taylor, C.

1981-10-01

The work reported here addressed the problem of improving the critical current characteristic of a comercial multifilamentary Nb 3 Sn strand by varying its heat treatment. The work was done from the perspective that the critical current characteristic is controlled by the metallurgical state of the reacted layer, which is, in turn, fixed by the processing the wire has undergone. The research was carried out in parallel with metallographic studies which analyzed the microstructure and composition profile within the reacted Nb 3 Sn layer as a function of heat treatment. The combined results of metallographic and processing research suggest that it is possible to engineer the microstructure of the reacted layer to improve J/sub c/(H). The specific product of the work is a tailored double-aging treatment which introduces a favorable combination of microstructure and composition in the reacted layer and causes a substantial improvement in the critical current characteristic of the strand

Calibration of Hall sensor array for critical current measurement of YBCO tape with ferromagnetic substrate

Energy Technology Data Exchange (ETDEWEB)

Zhu, Yunpeng; Wang, Gang; Liu, Liyuan [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Yang, Xinsheng, E-mail: xsyang@swjtu.edu.cn [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Zhao, Yong [Key laboratory of Magnetic levitation Technologies and Maglev Trains (Ministry of Education), Superconductor and New Energy R& D Center, Mail Stop 165#, Southwest Jiaotong University, Chengdu, 610031 (China); Superconductivity Research Group, School of Materials Science and Engineering, University of New South Wale, Sydney 2052, NSW (Australia)

2015-12-15

Abstract : HAS (Hall sensor array) is a powerful tool to detect the uniformity of HTS (high temperature superconductor) tape through mapping the distribution of remanent or shielding field along the surface of the tape. However, measurement of HTS tape with ferromagnetic parts by HSA is still an issue because the ferromagnetic substrate has influence on the magnetic field around the HTS layer. In this work, a continuous HSA system has been designed to measure the critical current of the YBCO tape with ferromagnetic substrate. The relationship between the remanent field and critical current was calibrated by the finite element method. The result showed that the HSA is an effective method for evaluating the critical current of the HTS tape with ferromagnetic substrate. - Highlight: • A continuous Hall sensor array system has been designed. • The inhomogeneity of YBCO tape with ferromagnetic substrate can be detected by HAS. • Finite element method is an effective method for calibrating the remanent field.

Critical tunnel currents and dissipation of Quantum-Hall bilayers in the excitonic condensate state

International Nuclear Information System (INIS)

Yoon, Y; Huang, X; Yarar, E; Dietsche, W; Tiemann, L; Schmult, S; Klitzing, K v

2011-01-01

Transport and tunneling is studied in the regime of the excitonic condensate at total filling factor one using the counterflow geometry. At small currents the coupling between the layers is large making the two layers virtually electrically inseparable. Above a critical current the tunneling becomes negligible. An onset of dissipation in the longitudinal transport is observed in the same current range.

Critical currents and flux-pinning properties in PbMo6S8 superconductors

International Nuclear Information System (INIS)

Noto, K.; Hamasaki, K.; Komata, T.; Saito, T.; Watanabe, K.; Yamashita, T.

1986-01-01

We report on recent investigations of the fabrication of PbMo 6 S 8 tapes prepared using an electro-plating and diffusion technique. Measurement of critical currents was carried out in either 16.5 T superconducting magnet, or 20.5 T (HM-3) and 23 T (HM-2) hybrid magnets in High Field Laboratory for Superconducting Materials RIISOM, Tohoku University in Japan. After optimal reaction the critical temperature measured by a resistive method reaches about 14.5 K, and a transition width was less than 0.5 K. Critical current densities are relatively high in a low magnetic field, and reached 1X10 4 A/cm 2 in a 15 T magnetic field at 4.2 K. However, J /SUB c/ 's in a strong magnetic field above 15 T are still insufficient for practical applications. In some of these samples pinning force densities were found to obey a simple scaling law, and in most cases the scaling is not obey. Poor J /SUB c/ -B characteristics in a strong magnetic field may be due to inhomogeneities of this compound

How States Can Promote Local Innovation, Options, and Problem-Solving in Public Education. Linking State and Local School Improvement

Science.gov (United States)

Posamentier, Jordan; Lake, Robin; Hill, Paul

2017-01-01

State policy plays a critical role in determining whether and how well local education improvement strategies can be implemented. As states rework their education policies under the Every Student Succeeds Act (ESSA), state and local leaders need a way to assess their current policy environment and identify the changes needed to encourage local…

The potential of large critical currents in the high Tc oxides

International Nuclear Information System (INIS)

Deutcher, G.

1993-01-01

The potential for high critical current densities is examined. on a thermodynamical basis, the energy scale for vortex pinning can be derived for instance from a measurement of the width of the critical region. This energy scale is of the order of 0.2 eV in YBCO, which is sufficient for practical applications. Another important parameter is the short coherence length. The inner plane length, of the order of a few lattice spacing, is favorable for pinning by point defects. But the very short outer plane length gives rise to anomalous magnetic behavior, unfavorable for high-field applications at high temperature; this is true in particular in most anisotropic oxides, such as the Bi compounds (author)

Fabrication of Ba-K-Bi-O thick film artefacts with improved critical currents

International Nuclear Information System (INIS)

Moore, J.C.; Salter, C.J.; Jenkins, R.J.; Grovenor, C.R.M.; Jones, H.

1993-01-01

The Ba-K-Bi-O system has a maximum T c of around 30K for a composition of Ba 0.6 K 0.4 BiO 3 . Fabrication of good quality single phase samples is extremely difficult and requires careful control of the fabrication conditions. Successful synthesis procedures for Ba-K-Bi-O powder and melt cast material which allow some control of the potassium content of the product were established by Hinks et al. The process is based on a melt and sinter step in an inert atmosphere which creates oxygen vacancies and allows potassium to enter the lattice. The oxygen vacancies are then filled by a subsequent oxygen anneal to obtain superconductivity. Ba-K-Bi-O is, therefore, metastable and consequently difficult to synthesise. There have been few reports of transport measurements and even fewer reports of transport critical currents for bulk material. It is often accepted that Ba-K-Bi-O has an intrinsically low critical current, and extremely poor critical current densities of 0.05 Acm -2 have been quoted for melt cast material. It has been suggested that the presence of weak links is the cause. However, there has been little research into the relationship between process conditions and superconducting properties for melt processed Ba-K-Bi-O to confirm this. (orig.)

Influence of electron spectrum dielectrizations on critical current of the Josephson medium BaPb1-xBixO3

International Nuclear Information System (INIS)

Vojtenko, A.I.; Gabovich, A.M.; Moiseev, D.P.; Postnikov, V.M.; Shpigel', A.S.

1990-01-01

Temperature dependences of the critical current I c across the symmetrical tunnel Josephson junctions between superconductors with partially-gapped electron spectrum were calculated. Densities J c of the critical current for the bulk Josephson-type samples and current-voltage characteristics of the tunnel-type were measured

The critical current density of an SNS Josephson-junction in high magnetic fields

International Nuclear Information System (INIS)

Carty, George J; Hampshire, Damian P

2013-01-01

Although the functional form of the critical current density (J c ) of superconducting–normal–superconducting (SNS) Josephson-junctions (J-Js) has long been known in the very low field limit (e.g. the sinc function), includes the local properties of the junction and has been confirmed experimentally in many systems, there have been no such general solutions available for high fields. Here, we derive general analytic equations for J c in zero field and in high fields across SNS J-Js for arbitrary resistivity of the superconductor and the normal layer which are consistent with the literature results available in limiting cases. We confirm the validity of the approach using both computational solutions to time-dependent Ginzburg–Landau (TDGL) theory applied to SNS junctions and experimental J c data for an SNS PbBi–Cd–PbBi junction. We suggest that since SNS junctions can be considered the basic building blocks for the description of the grain boundaries of polycrystalline materials because they both provide flux-flow channels, this work may provide a mathematical framework for high J c technological polycrystalline superconductors in high magnetic fields. (paper)

Higher spin currents in the critical O(N) vector model at 1/N2

International Nuclear Information System (INIS)

Manashov, A.N.; Strohmaier, M.

2017-06-01

We calculate the anomalous dimensions of higher spin singlet currents in the critical O(N) vector model at order 1/N 2 . The results are shown to be in agreement with the four-loop perturbative computation in φ 4 theory in 4-2ε dimensions. It is known that the order 1/N anomalous dimensions of higher-spin currents happen to be the same in the Gross-Neveu and the critical vector model. On the contrary, the order 1/N 2 corrections are different. The results can also be interpreted as a prediction for the two-loop computation in the dual higher-spin gravity.

Critical report of current fisheries management measures implemented for the North Sea mixed demersal fisheries

DEFF Research Database (Denmark)

Nielsen, J. Rasmus; Ulrich, Clara; Hegland, Troels J.

The present report is an EU-FP7-SOCIOEC Report giving an overview and critical evaluation of the current management measures implemented for the North Sea mixed demersal fisheries and the fish stocks involved in this. Also, this involves review and critical evaluation of the scientific advice...

Influence of the current-phase relation on the critical-current-applied-magnetic-flux dependence in parallel-connected Josephson junctions

International Nuclear Information System (INIS)

Tsang, W.; Van Duzer, T.

1976-01-01

The form of the current-phase relations for the Josephson junctions is shown to have a significant influence on the relation I/sub c/(theta/sub a/) between critical current and applied flux for two junctions connected in parallel in a superconducting circuit. The observed one-flux-quantum periodicity and inversion symmetry of the I/sub c/(theta/sub a/) relation are shown to result from the fact that the current-phase, i-phi, relations of the junctions satisfy i (phi+2mπ) =i (phi) and i (-phi) =-i (phi), respectively. It is also shown that if the current-phase relations for the two junctions are different, an asymmetry appears in the I/sub c/(theta/sub a/)

Critical Velocity for Shear Localization in A Mature Mylonitic Rock Analogue

Science.gov (United States)

Takahashi, M.; van den Ende, M.; Niemeijer, A. R.; Spiers, C. J.

2016-12-01

Highly localized slip zones, seen within ductile shear zones developed in nature, such as pseudotachylite bands occurring within mylonites, are widely recognized as evidence for earthquake nucleation and/or propagation within and overprinting the ductile regime. To understand brittle/frictional localization processes in ductile shear zones and to connect these to earthquake nucleation and propagation processes, we performed large velocity step-change tests on a brine-saturated, 80:20 (wt. %) halite and muscovite gouge mixture, after forming a mature mylonitic structure through pressure solution creep at low-velocity. The sharp increase in sliding strength that occurs in response to an instantaneous upward velocity-step (direct effect) is an important parameter in determining the potential for and nature of seismic rupture nucleation. We obtained reproducible results regarding low velocity mechanical behavior compared with previous work of Niemeijer and Spiers, [2006], but also obtained new insights into the effects of sudden increases in slip velocity on localization and strength evolution, at velocities above a specific critical velocity Vc ( 20 μm/sec). We found that once a ductile, mylonitic structure has developed in a shear zone, subsequent cataclastic deformation at high velocity (> Vc) is consistently localized in a narrow zone characterized by fine grains of halite aligned in arrays between foliated muscovite Due to this intense localization, structures presumably developed under low velocity conditions were still preserved in large parts of the gouge body. This switch to localized deformation is controlled by the imposed velocity, and becomes most apparent at velocities over Vc. In addition, the direct effect a decreases rapidly when the velocity exceeds Vc. This implies that slip can localize and accelerate towards seismic velocities more or less instantly once Vc is exceeded. Obtaining a measure for Vc in natural faults is therefore of key importance

Improved critical current densities and compressive strength in porous superconducting structures containing calcium

International Nuclear Information System (INIS)

Walsh, D; Hall, S R; Wimbush, S C

2008-01-01

Templated control of crystallization by biopolymers is a new technique in the synthesis of high temperature superconducting phases. By controlling the way YBa 2 Cu 3 O 7-δ (Y123) materials crystallize and are organized in three dimensions, the critical current density can be improved. In this work, we present the results of doping superconducting sponges with calcium ions, which result in higher critical current densities (J c ) and improved compressive strength compared to that of commercially available Y123, in spite of minor reductions in T c . Y123 synthesis using the biopolymer dextran achieves not only an extremely effective oxygenation of the superconductor but also an in situ template-directing of the crystal morphology producing high J c , homogeneous superconducting structures with nano-scale crystallinity

What happens in Josephson junctions at high critical current densities

Science.gov (United States)

Massarotti, D.; Stornaiuolo, D.; Lucignano, P.; Caruso, R.; Galletti, L.; Montemurro, D.; Jouault, B.; Campagnano, G.; Arani, H. F.; Longobardi, L.; Parlato, L.; Pepe, G. P.; Rotoli, G.; Tagliacozzo, A.; Lombardi, F.; Tafuri, F.

2017-07-01

The impressive advances in material science and nanotechnology are more and more promoting the use of exotic barriers and/or superconductors, thus paving the way to new families of Josephson junctions. Semiconducting, ferromagnetic, topological insulator and graphene barriers are leading to unconventional and anomalous aspects of the Josephson coupling, which might be useful to respond to some issues on key problems of solid state physics. However, the complexity of the layout and of the competing physical processes occurring in the junctions is posing novel questions on the interpretation of their phenomenology. We classify some significant behaviors of hybrid and unconventional junctions in terms of their first imprinting, i.e., current-voltage curves, and propose a phenomenological approach to describe some features of junctions characterized by relatively high critical current densities Jc. Accurate arguments on the distribution of switching currents will provide quantitative criteria to understand physical processes occurring in high-Jc junctions. These notions are universal and apply to all kinds of junctions.

Field mapping measurements to determine spatial and field dependence of critical current density in YBCO tapes

International Nuclear Information System (INIS)

Leclerc, J.; Berger, K.; Douine, B.; Lévêque, J.

2013-01-01

Highlights: • A method for characterizing superconducting tapes from field mapping is presented. • A new and efficient field mapping apparatus has been setup. • This method allows the spatial characterization of superconducting tapes. • The critical current density is obtained as a function of the flux density. • This method has been experimentally tested on an YBCO tape. -- Abstract: In this paper a measurement method that allows the determination of the critical current density of superconducting tape from field mapping measurements is presented. This contact-free method allows obtaining characteristics of the superconductor as a function of the position and of the applied flux density. With some modifications, this technique can be used for reel-to-reel measurements. The determination of the critical current density is based on an inverse calculation. This involves calculating the current distribution in the tape from magnetic measurements. An YBaCuO tape has been characterized at 77 K. A defect in this superconductor has been identified. Various tests were carried out to check the efficiency of the method. The inverse calculation was tested theoretically and experimentally. Comparison with a transport current measurement was also performed

Experimental and numerical study of influence of ferromagnetic cover on critical current of BiSCCO-2223/Ag tape superconductor

International Nuclear Information System (INIS)

Vojenciak, M; Souc, J; Goemoery, F

2009-01-01

Samples of commercially available BiSCCO-2223/Ag tape have been partially covered by the ferromagnetic material. Improvement of the self-field critical current up to 15 % has been achieved by this procedure. A critical current of such tape strongly depends on geometric and magnetic properties of both, the superconducting tape as well as the ferromagnetic cover. Numerical simulations, based on the critical state model using commercial finite element method (FEM) code, have been performed. Properties of superconductor are characterized by anisotropic dependence of the critical current density on magnetic field as well as detail geometry of filaments. The ferromagnetic material is characterized by nonlinear magnetization curve. Nonlinear dependences of the critical current on selected parameters are shown in this work. Optimization of the cover parameters using these curves has been made. Samples with various parameters have been manufactured for the confirmation of numerical simulations results. Experimental results are in good qualitative agreement with results obtained by numerical simulations.

Influence of two-stage annealing treatment on critical current of bronze-processed multifilamentary Nb/sub 3/Sn superconducting materials

International Nuclear Information System (INIS)

Ochiai, S.; Osamura, K.; Ryoji, M.

1987-01-01

The influence of changes of volume fraction of Nb/sub 3/Sn, grain size and upper critical magnetic field due to two-stage annealing treatment (low temperature annealing to form fine grains + high temperature annealing to raise upper critical magnetic field) on overall critical current and critical current density were studied at magnetic field of 3-15 T. When annealing temperature was low (773-923 K) and the volume fraction of Nb/sub 3/Sn was low in first stage annealing, second stage annealing could raise the overall critical current over the range of the applied magnetic field due to increase in upper critical magnetic field H/sub c2/ and volume fraction of Nb/sub 3/Sn accompanying with reduction in Sn concentration in the bronze matrix, which played a role to reduce residual strain in Nb/sub 3/Sn, leading to high H/sub c2/ although the loss in pinning force arose from the coarsening of the grains. When the annealing temperature was high (973 K) and the Nb/sub 3/Sn was formed until the Sn was consumed in the first stage, second stage annealing could not raise the critical current due to increase in grain size and no effective increase in H/sub c2/. The critical current density at low magnetic fields below several Teslas was reduced by the second stage annealing due to increase in grain size but that at high fields was raised due to increase in high H/sub c2/. The reverse two-stage annealing treatment (high temperature annealing in the first stage+low temperature annealing in the second stage) reduced the H/sub c2/ slightly with increasing second stage annealing temperature and time. The critical current density at low magnetic fields was determined mainly by the grain size and that at high fields was determined by the combination of the upper critical field and grain size

Higher critical current density achieved in Bi-2223 High-Tc superconductors

Directory of Open Access Journals (Sweden)

M.S. Shalaby

2016-07-01

Full Text Available Bi2Sr2Ca2Cu3Ox (Bi-2223 were prepared using a solid state reaction method at different sintering times and temperatures. Structural phase identifications have been done using X-Ray analysis and refinement by Reitveld method which proves the coexistence of Bi-2223 and Bi-2212 phases. The critical transition temperature Tc and critical current density Jc values were measured using superconducting quantum interference device magnetometer (SQUID and by the magneto-optics technique. A remarkable rapid decrease to the diamagnetic signal in the magnetization versus temperature M(T at 110 K and Jc around 1.2 × 107 A/m2 at 5 K are confirmed for the Bi-2223 compound.

ac loss and dc critical current densities of Nb3Sn tapes by the solid state diffusion process

International Nuclear Information System (INIS)

Suenaga, M.; Klamut, C.; Bussiere, J.F.

1976-01-01

The effects of metallurgical processing on 60 Hz ac losses and dc critical currents in Nb 3 Sn tapes fabricated by the solid state diffusion technique were investigated. An addition of Al to the Cu--Sn alloy for the matrix resulted in large reduction in the ac losses of Nb 3 Sn tapes, but the highest linear critical current densities were observed in Nb 3 Sn tapes produced with a Nb-1 wt percent Zr core in a Cu-13 wt percent Sn matrix. Values of the losses and the critical currents in these tapes can meet the present requirements for the ac superconducting power cables

Exponential temperature dependence of the critical transport current in Y-Ba-Cu-O thin films

International Nuclear Information System (INIS)

Yom, S.S.; Hahn, T.S.; Kim, Y.H.; Chu, H.; Choi, S.S.

1989-01-01

We have measured the critical currents in rf-sputtered YBa 2 Cu 3 O/sub 7-x/ thin films deposited on polycrystalline yttria-stabilized zirconia substrates as a function of temperature down to 10 K. The dependence of the granular films at low temperature indicated exponential behavior which is similar to the superconductor-normal metal-superconductor (S-N-S) type tunneling junctions. For the films with a grain size of approximately 1 μm, we observed two exponential decay constants, which suggest that Josephson junctions limiting the transport critical current are possible both at the grain boundaries and at twin boundaries

Critical current density of four-CuO2-layer T1Ba2Ca3Cu4O11-δ

International Nuclear Information System (INIS)

Zhang, L.; Liu, J.Z.; Shelton, R.N.

1998-01-01

Full text: A key requirement for technological application is to have superconductors with high critical current density at practical operating temperatures and magnetic fields. The critical current density is strongly related to underlying properties of high T c superconductors, such as layering, anisotropy and other intrinsic material structures. The thallium-based superconductors attracted much attention at early stage mainly due to their high superconducting transitions. Recent studies show that these materials appear to be a better choice for achieving higher critical current density because of a stronger interlayer coupling between superconducting layers. Single crystals of TlBa 2 Ca 3 Cu 4 O 11-δ were grown by a self-flux method. This material is a strong-layered superconductor with four-CuO 2 -planes in a unit cell and a superconducting transition temperature of 128K. Our experimental results show that TlBa 2 Ca 3 Cu 4 O 11-δ crystals have high irreversibility line, large critical current density and high upper critical field. The impact of layering and the number of Cu-O layers on flux pinning, critical current density and other magnetic properties will also be discussed

Study of critical beta non-circular tokamak equilibria sustained in steady state by beam driven currents

International Nuclear Information System (INIS)

Okano, K.; Ogawa, Y.; Naitou, H.

1988-07-01

A new MHD-equilibrium/current-drive analysis code was developed to analyse the high beta tokamak equilibria consistent with the beam driven current profiles. In this new code, the critical beta equilibrium, which is stable against the ballooning mode, the kink mode and the Mercier mode, is determined first using MHD equilibrium and stability analysis codes (EQLAUS/ERATO). Then, the current drive parameters and the plasma parameters, required to sustain this critical beta equilibrium, are determined by iterative calculations. The beam driven current profiles are evaluated by the Fokker-Planck calculations on individual flux surfaces, where the toroidal effects on the beam ion and plasma electron trajectories are considered. The pressure calculation takes into account the beam ion and fast alpha components. A peculiarity of our new method is that the obtained solution is not only consistent with the MHD equilibrium but also consistent with the critical beta limit conditions, in the current profile and the pressure profile. Using this new method, β ∼ 21 % bean and β ∼ 6 % D-type critical beta equilibria were scanned for various parameters; the major radius, magnetic field, temperature, injection energy, etc. It was found that the achievable Q value for the bean type was always about 30 % larger than for the D-type cases, where Q = fusion power/beam power. With strong beanness, Q ∼ 6 for DEMO type tokamaks (∼500 MWth) and Q ∼ 20 for power reactor size (4.5 GWth) are achievable. On the other hand, the Q value would not exceed sixteen for the D-type machines. (author)

Critical condition for current-driven instability excited in turbulent heating of TRIAM-1 tokamak plasma

Energy Technology Data Exchange (ETDEWEB)

Nakamura, Y; Watanabe, T; Nagao, A; Nakamura, K; Kikuchi, M; Aoki, T; Hiraki, N; Itoh, S [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Mitarai, O

1982-02-01

Critical condition for current-driven instability excited in turbulently heated TRIAM-1 tokamak plasma is investigated experimentally. Resistive hump in loop voltage, plasma density fluctuation and rapid increase of electron temperature in a skin layer are simultaneously observed at the time when the electron drift velocity amounts to the critical drift velocity for low-frequency ion acoustic instability.

Advanced electrical current measurements of microdischarges: evidence of sub-critical pulses and ion currents in barrier discharge in air

Science.gov (United States)

Synek, Petr; Zemánek, Miroslav; Kudrle, Vít; Hoder, Tomáš

2018-04-01

Electrical current measurements in corona or barrier microdischarges are a challenge as they require both high temporal resolution and a large dynamic range of the current probe used. In this article, we apply a simple self-assembled current probe and compare it to commercial ones. An analysis in the time and frequency domain is carried out. Moreover, an improved methodology is presented, enabling both temporal resolution in sub-nanosecond times and current sensitivity in the order of tens of micro-amperes. Combining this methodology with a high-tech oscilloscope and self-developed software, a unique statistical analysis of currents in volume barrier discharge driven in atmospheric-pressure air is made for over 80 consecutive periods of a 15 kHz applied voltage. We reveal the presence of repetitive sub-critical current pulses and conclude that these can be identified with the discharging of surface charge microdomains. Moreover, extremely low, long-lasting microsecond currents were detected which are caused by ion flow, and are analysed in detail. The statistical behaviour presented gives deeper insight into the discharge physics of these usually undetectable current signals.

Requirements on localized current drive for the suppression of neoclassical tearing modes

NARCIS (Netherlands)

Bertelli, N.; De Lazzari, D.; Westerhof, E.

2011-01-01

A heuristic criterion for the full suppression of an NTM was formulated as eta(NTM) = j(CD,max)/j(BS) >= 1.2 (Zohm et al 2005 J. Phys. Conf. Ser. 25 234), where j(CD,max) is the maximum in the driven current density profile applied to stabilize the mode and j(BS) is the local bootstrap current

CRITICAL RADAR: TOOL AND METHODOLOGY FOR EVALUATING CURRENT PROJECTS USING MULTIPLE VARIABLES

Directory of Open Access Journals (Sweden)

André M. Ferrari

2017-06-01

Full Text Available Many resources are invested in measurement processes of projects indicators without, however, give a clear view of which projects deserves the right attention at the right time. This paper proposes the use of statistics, through the analysis of multiple variables and their interrelationships, to give better basis to a critical assessment methodology of current projects used in a multinational mining company. The contribution of the research is to report the methodology called Critical Radar which is based on a graphical tool with simple operationalization that can support the decision making in complex environments, and has great flexibility across the different market scenarios and possible changes in companies guidelines. The tool has great potential to help evaluate current projects due to their characteristics of flexible use in different business areas; high degree of freedom for improvement; use of known market tool in its development; ease of viewing the results through charts and notes and user freedom to use any existing indicators in the company if complied with some statistical data quality characteristics.

Influence of the 3D-2D crossover on the critical current of Nb/Cu multilayers

DEFF Research Database (Denmark)

Krasnov, V. M.; Pedersen, Niels Falsig; Oboznov, V. A.

1994-01-01

We report the experimental observation of the Josephson critical current across layers, I(c) perpendicular-to, for Nb/Cu multilayers. Unique samples with a small cross section (20 mum in diameter) consisting of ten Nb/Cu junctions were fabricated for such measurements. A strong influence of the d......We report the experimental observation of the Josephson critical current across layers, I(c) perpendicular-to, for Nb/Cu multilayers. Unique samples with a small cross section (20 mum in diameter) consisting of ten Nb/Cu junctions were fabricated for such measurements. A strong influence...... of the dimensional 3D-2D cross-over on the I(c)perpendicular-to was observed. Thus, as the temperature becomes smaller than T2D, hysteresis in the current-voltage characteristic appears and the behavior of the temperature dependence of the I(c)perpendicular-to changes. For T > T2D the diminishing of the hysteresis...... is caused by a sharp decrease of the junction capacitance in the 3D regime when the sample becomes uniform across layers. Calculation of the critical-current temperature dependence I(c)perpendicular-to (T) for our multilayers was made. An agreement between experimental and theoretical dependencies I...

Microstructural and crystallographic imperfections of MgB2 superconducting wire and their correlation with the critical current density

Science.gov (United States)

Shahabuddin, Mohammed; Alzayed, Nasser S.; Oh, Sangjun; Choi, Seyong; Maeda, Minoru; Hata, Satoshi; Shimada, Yusuke; Hossain, Md Shahriar Al; Kim, Jung Ho

2014-01-01

A comprehensive study of the effects of structural imperfections in MgB2 superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB2 material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB2, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB2, however, even at low sintering temperature, and thus block current transport paths.

Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

Energy Technology Data Exchange (ETDEWEB)

Selvamanickam, V; Chen, Y; Shi, T; Liu, Y; Khatri, ND; Liu, J; Yao, Y; Xiong, X; Lei, C; Soloveichik, S; Galstyan, E; Majkic, G

2013-01-21

The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba2Cu3Ox film. By a modified MOCVD process,enhanced critical current densities have been achieved with high levels of Zr addition,including 3.83 MA cm(-2) in 15 at.% Zr- added 1.1 mu m thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/ 12 mm have been reached in (Gd,Y) BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape,corresponding to a pinning force value of 268 GN m(-3). The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second- phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met.

Enhanced critical currents in (Gd,Y)Ba2Cu3Ox superconducting tapes with high levels of Zr addition

International Nuclear Information System (INIS)

Selvamanickam, V; Shi, T; Liu, Y; Khatri, N D; Liu, J; Yao, Y; Galstyan, E; Majkic, G; Chen, Y; Xiong, X; Lei, C; Soloveichik, S

2013-01-01

The critical current and structural properties of (Gd,Y)BaCuO tapes made by metal organic chemical vapor deposition (MOCVD) with Zr addition levels up to 30 at.% have been investigated. The reduction in critical current beyond the previously optimized Zr addition level of 7.5 at.% was found to be due to structural deterioration of the (Gd,Y)Ba 2 Cu 3 O x film. By a modified MOCVD process, enhanced critical current densities have been achieved with high levels of Zr addition, including 3.83 MA cm −2 in 15 at.% Zr-added 1.1 μm thick film at 77 K in zero magnetic field. Critical currents as high as 1072 A/12 mm have been reached in (Gd,Y)BaCuO tapes with 15 at.% Zr addition at 30 K in a field of 3 T applied perpendicular to the tape, corresponding to a pinning force value of 268 GN m −3 . The enhanced critical currents achievable with a high density of nanoscale defects by employing high levels of second-phase additions enable the performance targets needed for the use of HTS tapes in coil applications involving high magnetic fields at temperatures below 50 K to be met. (paper)

Effect of localized states on the current-voltage characteristics of metal-semiconductor contacts with thin interfacial layer

Science.gov (United States)

Chattopadhyay, P.

1994-10-01

The role of discrete localized states on the current-voltage characteristics of metal-semiconductor contact is examined. It is seen that, because of these localized states, the logarithmic current vs voltage characteristics become nonlinear. Such nonlinearity is found sensitive to the temperature, and the energy and density of the localized states. The predicted temperature dependence of barrier height and the current-voltage characteristics are in agreement with the experimental results of Aboelfotoh [ Phys. Rev. B39, 5070 (1989)].

Higher spin currents in the critical O(N) vector model at 1/N{sup 2}

Energy Technology Data Exchange (ETDEWEB)

Manashov, A.N. [Hamburg Univ. (Germany). 2. Inst. fuer Theoretische Physik; Regensburg Univ. (Germany). Inst. fuer Theoretische Physik; Skvortsov, E.D. [Munich Univ. (Germany). Arnold Sommerfeld Center for Theoretical Physics; Lebedev Institute of Physics, Moscow (Russian Federation); Strohmaier, M. [Regensburg Univ. (Germany). Inst. fuer Theoretische Physik

2017-06-15

We calculate the anomalous dimensions of higher spin singlet currents in the critical O(N) vector model at order 1/N{sup 2}. The results are shown to be in agreement with the four-loop perturbative computation in φ{sup 4} theory in 4-2ε dimensions. It is known that the order 1/N anomalous dimensions of higher-spin currents happen to be the same in the Gross-Neveu and the critical vector model. On the contrary, the order 1/N{sup 2} corrections are different. The results can also be interpreted as a prediction for the two-loop computation in the dual higher-spin gravity.

Temperature dependence of critical current and transport current losses of 4 mm YBCO coated conductors manufactured using nonmagnetic substrate

Science.gov (United States)

Kvitkovic, J.; Hatwar, R.; Pamidi, S. V.; Fleshler, S.; Thieme, C.

2015-12-01

The temperature dependence of the critical current and AC losses were measured on American Superconductor Corporation's (AMSC) second generation high temperature superconducting (2G HTS) wire produced by Rolling Assisted Biaxially Textured Substrate (RABiTS) and Metal Organic Deposition (MOD) process. Wires manufactured with two types of substrates were characterized. The magnetic substrate with composition Ni5a%W exhibits a magnetic signature and has non-negligible AC losses in AC power applications. A new nonmagnetic substrate with an alloy composition Ni9a%W has been developed by AMSC to address the AC losses in 2G HTS. The data presented show that the performance of the new conductor is identical to the conductor with magnetic substrate in terms of critical current density. The data on AC losses demonstrate the absence of ferromagnetic loss component in the new conductor and significantly reduced AC losses at low to moderate values of I/Ic. The reduced losses will translate into reduced capital costs and lower operating costs of superconducting electrical devices for AC applications.

Eddy current testing device for metallic tubes at least locally curved

International Nuclear Information System (INIS)

Pigeon, Marcel; Vienot, Claude.

1975-01-01

Steam generators, condensers and heat exchangers generally consist of metallic tube bundles, the tubes having a complex geometry. The invention concerns an Eddy current testing device for metallic tubes at least locally curved, operating by translation of a probe inside the tubes [fr

Theory of flux cutting and flux transport at the critical current of a type-II superconducting cylindrical wire

International Nuclear Information System (INIS)

Clem, John R.

2011-01-01

I introduce a critical-state theory incorporating both flux cutting and flux transport to calculate the magnetic-field and current-density distributions inside a type-II superconducting cylinder at its critical current in a longitudinal applied magnetic field. The theory is an extension of the elliptic critical-state model introduced by Romero-Salazar and Perez-Rodriguez. The vortex dynamics depend in detail on two nonlinear effective resistivities for flux cutting (ρ(parallel)) and flux flow (ρ(perpendicular)), and their ratio r = ρ(parallel)/ρ(perpendicular). When r c (φ) that makes the vortex arc unstable.

Field-dependent transport critical current in single crystals of Ba(Fe1-xTMx)2As2 (TM = Co, Ni) superconductors

International Nuclear Information System (INIS)

Tanatar, M A; Ni, N; Bud'ko, S L; Canfield, P C; Prozorov, R

2010-01-01

Critical current density was studied by direct electrical transport measurements in single crystals of Ba(Fe 1-x TM x ) 2 As 2 under magnetic fields up to 9 T. To understand the relation of the critical current to the structural transformations in the material, the electron doping level was controlled by the amount of TM = Co (underdoped x = 0.054 versus optimally doped x = 0.074) and by the nature of the dopant (optimally doped TM = Co versus TM = Ni). It is found that the suppression of the critical current density by the magnetic field is much slower for Ni and underdoped Co compositions than for an optimally doped Co composition. We relate this difference to the proximity to the orthorhombic/antiferromagnetic phase boundary in the T(x) phase diagram. Structural domains formed in this area of the phase diagram create favorable conditions for pinning and not only increase critical current densities, but also hamper the degradation of the critical current under magnetic field.

Hysteresis of critical currents of superconducting bridges in low perpendicular magnetic fields

International Nuclear Information System (INIS)

Aomine, T.; Tanaka, E.; Yamasaki, S.; Tani, K.; Yonekura, A.

1989-01-01

Hysteresis of critical currents I c of superconducting bridges with In, Nb, and NbN has been studied in low perpendicular magnetic fields. Influences of bridge geometry, small field sweep, trapped flux, and bombardment of argon ions on the hysteresis were made clear. The experimental results suggest that the edge pinning and trapped flux in the bank of bridges are associated with the hysteresis. The peak value of I c of NbN bridges, as well as granular Al and In bridges reported before, in decreasing fields agrees with the calculated pair-breaking current. The origin of the hysteresis is discussed

Dependence of critical current density on crystalline direction in thin YBCO films

DEFF Research Database (Denmark)

Paturi, P.; Peurla, M.; Raittila, J.

2005-01-01

The dependence of critical current density (J(c)) on the angle between the current direction and the (100) direction in the ab-plane of thin YBCO films deposited on (001)-SrTiO3 from natiocrystalline and microcrystalline targets is studied using magneto-optical microscopy. In the films made from...... the nanocrystalline target it is found that J(c) does not depend on the angle whereas J(c) decreases with increasing angle in the films made from the microcrystalline target. The films were characterized by detailed X-ray diffraction measurements. The findings are explained in terms of a network of planar defects...

Recalled peer relationship experiences and current levels of self-criticism and self-reassurance.

Science.gov (United States)

Kopala-Sibley, Daniel C; Zuroff, David C; Leybman, Michelle J; Hope, Nora

2013-03-01

Numerous studies have shown that personality factors may increase or decrease individuals' vulnerability to depression, but little research has examined the role of peer relationships in the development of these factors. Accordingly, this study examined the role of recalled parenting and peer experiences in the development of self-criticism and self-reassurance. It was hypothesized that, controlling for recalled parenting behaviours, specific recalled experiences of peer relationships would be related to current levels of specific forms of self-criticism and self-reassurance. Hypotheses were tested using a retrospective design in which participants were asked to recall experiences of parenting and peer relationships during early adolescence. This age was chosen as early adolescence has been shown to be a critical time for the development of vulnerability to depression. A total of 103 female and 97 male young adults completed measures of recalled parenting, overt and relational victimization and prosocial behaviour by peers, and current levels of self-criticism and self-reassurance. Hierarchical regression analyses showed that parents and peers independently contributed to the development of self-criticism and self-reassurance. Specifically, controlling for parental care and control, overt victimization predicted self-hating self-criticism, relational victimization predicted inadequacy self-criticism, and prosocial behaviour predicted self-reassurance. As well, prosocial behaviour buffered the effect of overt victimization on self-reassurance. Findings highlight the importance of peers in the development of personality risk and resiliency factors for depression, and suggest avenues for interventions to prevent the development of depressive vulnerabilities in youth. The nature of a patient's personality vulnerability to depression may be better understood through a consideration of the patient's relationships with their peers as well as with parents during

Local electromagnetic waves in layered superconductors

International Nuclear Information System (INIS)

Gvozdikov, V.M.; Vega-Monroy, R.

1999-01-01

A dispersion equation for electromagnetic waves localized on a defect layer of a layered superconductor is obtained in the frame of a model which neglects electron hopping between layers but assumes an arbitrary current-current response function within the layers. The defect layer differs from the rest of the layers by density and mass of charge carriers. It is shown that near the critical temperature in the London limit the local mode lies within the superconducting gap and has a wave vector threshold depending on the layered crystal and defect layer parameters. In the case of highly anisotropic layered superconductors, like Bi- or Tl-based high-T c cuprates, the local mode exists within a narrow range of positive variations of the mass and charge carriers. (author)

A one-dimensional model to describe flow localization in viscoplastic slender bars subjected to super critical impact velocities

Science.gov (United States)

Vaz-Romero, A.; Rodríguez-Martínez, J. A.

2018-01-01

In this paper we investigate flow localization in viscoplastic slender bars subjected to dynamic tension. We explore loading rates above the critical impact velocity: the wave initiated in the impacted end by the applied velocity is the trigger for the localization of plastic deformation. The problem has been addressed using two kinds of numerical simulations: (1) one-dimensional finite difference calculations and (2) axisymmetric finite element computations. The latter calculations have been used to validate the capacity of the finite difference model to describe plastic flow localization at high impact velocities. The finite difference model, which highlights due to its simplicity, allows to obtain insights into the role played by the strain rate and temperature sensitivities of the material in the process of dynamic flow localization. Specifically, we have shown that viscosity can stabilize the material behavior to the point of preventing the appearance of the critical impact velocity. This is a key outcome of our investigation, which, to the best of the authors' knowledge, has not been previously reported in the literature.

Fatigue-damage evolution and damage-induced reduction of critical current of a Nb3Al superconducting composite

International Nuclear Information System (INIS)

Ochiai, S; Sekino, F; Sawada, T; Ohno, H; Hojo, M; Tanaka, M; Okuda, H; Koganeya, M; Hayashi, K; Yamada, Y; Ayai, N; Watanabe, K

2003-01-01

We have studied the fatigue-damage mechanism of a Nb 3 Al superconducting composite at room temperature, and the influences of the fatigue damages introduced at room temperature on the critical current at 4.2 K and the residual strength at room temperature. The main (largest) fatigue crack arose first in the clad copper and then extended into the inner core with an increasing number of stress cycles. The cracking of the Nb 3 Al filaments in the core region occurred at a late stage (around 60-90% of the fatigue life). Once the fracture of the core occurred, it extended very quickly, resulting in a quick reduction in critical current and the residual strength with increasing stress cycles. Such a behaviour was accounted for by the crack growth calculated from the S-N curves (the relation of the maximum stress to the number of stress cycles at failure) combined with the Paris law. The size and distribution of the subcracks along the specimen length, and therefore the reduction in critical current of the region apart from the main crack, were dependent on the maximum stress level. The large subcracks causing fracture of the Nb 3 Al filaments were formed when the maximum stress was around 300-460 MPa, resulting in large reduction in critical current, but not when the maximum stress was outside such a stress range

The influence of vortex pinning and grain boundary structure on critical currents across grain boundaries in YBa2Cu3Ox

International Nuclear Information System (INIS)

Miller, D. J.

1998-01-01

We have used studies of single grain boundaries in YBCO thin films and bulk bicrystals to study the influence of vortex pinning along a grain boundary on dissipation. The critical current density for transport across grain boundaries in thin films is typically more than an order of magnitude larger than that measured for transport across grain boundaries in bulk samples. For low disorientation angles, the difference in critical current density within the grains that form the boundary can contribute to the substantial differences in current density measured across the boundary. However, substantial differences exist in the critical current density across boundaries in thin film compared to bulk bicrystals even in the higher angle regime in which grain boundary dissipation dominates. The differences in critical current density in this regime can be understood on the basis of vortex pinning along the boundary

Anisotropy of the critical current in MgB₂ tapes made of high energy milled precursor powder

DEFF Research Database (Denmark)

Hässler, W.; Kovac, P.; Eisterer, M.

2010-01-01

For applications of MgB2 wires or tapes, high critical currents in high magnetic fields are essential. By using tapes in superconducting coils the anisotropic behaviour of the critical current, i.e. the dependence on the direction of the external field in relation to the tape surface, has to be t...

Large critical current density improvement in Bi-2212 wires through the groove-rolling process

International Nuclear Information System (INIS)

Malagoli, A; Bernini, C; Braccini, V; Romano, G; Putti, M; Chaud, X; Debray, F

2013-01-01

Recently there has been a growing interest in Bi-2212 superconductor round wire for high magnetic field use despite the fact that an increase of the critical current is still needed to boost its successful use in such applications. Recent studies have demonstrated that the main obstacle to current flow, especially in long wires, is the residual porosity inside these powder-in-tube processed conductors that develops from bubble agglomeration when the Bi-2212 melts. In this work we tried to overcome this issue affecting the wire densification by changing the deformation process. Here we show the effects of groove rolling versus the drawing process on the critical current density J C and on the microstructure. In particular, groove-rolled multifilamentary wires show a J C increased by a factor of about 3 with respect to drawn wires prepared with the same Bi-2212 powder and architecture. We think that this approach in the deformation process is able to produce the required improvements both because the superconducting properties are enhanced and because it makes the fabrication process faster and cheaper. (paper)

Superconductivity, critical current density, and flux pinning in MgB2-x(SiC)x/2 superconductor after SiC nanoparticle doping

Science.gov (United States)

Dou, S. X.; Pan, A. V.; Zhou, S.; Ionescu, M.; Wang, X. L.; Horvat, J.; Liu, H. K.; Munroe, P. R.

2003-08-01

We investigated the effect of SiC nanoparticle doping on the crystal lattice structure, critical temperature Tc, critical current density Jc, and flux pinning in MgB2 superconductor. A series of MgB2-x(SiC)x/2 samples with x=0-1.0 were fabricated using an in situ reaction process. The contraction of the lattice and depression of Tc with increasing SiC doping level remained rather small most likely due to the counterbalancing effect of Si and C co-doping. The high level Si and C co-doping allowed the creation of intragrain defects and highly dispersed nanoinclusions within the grains which can act as effective pinning centers for vortices, improving Jc behavior as a function of the applied magnetic field. The enhanced pinning is mainly attributable to the substitution-induced defects and local structure fluctuations within grains. A pinning mechanism is proposed to account for different contributions of different defects in MgB2-x(SiC)x/2 superconductors.

Experiment to measure the effects of biaxial strain on the critical current of NbTi superconductor

International Nuclear Information System (INIS)

Froelich, K.J.

1975-01-01

Twisted multifilament, copper-clad NbTi superconductors have been axially and biaxially strained at 4.2K with a 7.5T background field. A simply-constructed cryogenic loading frame was built and used to strain the conductor. Results on 1.27 mm x 3.13 mm conductor have shown that degradation of less than .3 percent of critical current occurred when the wire was biaxially strained to +3260 μepsilon in the axial direction and -1875 μepsilon in the transverse direction. Degradation approaches 3 percent of critical current at approximately 6000 μepsilon in the axial direction only

Majorana splitting from critical currents in Josephson junctions

Science.gov (United States)

Cayao, Jorge; San-Jose, Pablo; Black-Schaffer, Annica M.; Aguado, Ramón; Prada, Elsa

2017-11-01

A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (LN≪ξ , where LN is the junction length and ξ is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effect.

Development of Bi-based high critical current density superconducting tapes

International Nuclear Information System (INIS)

Swaminathan, G.

1995-01-01

In order to achieve the aim of developing suitable superconducting materials the main emphasis has to be made in the following areas viz., synthesizing powders, detailed study of sintering and phase conversion process in relation to the critical current density (J c ) on pellets and optimising of tape processing parameters. The bismuth system has been found to be more favourable for making wires and tapes because of its high transition temperature, good stability, does not require oxygen on cooling and is non-toxic. These have been the most convenient properties which made the BiSCO material the most popular one

DROPOUTS IN SOLAR ENERGETIC PARTICLES: ASSOCIATED WITH LOCAL TRAPPING BOUNDARIES OR CURRENT SHEETS?

International Nuclear Information System (INIS)

Seripienlert, A.; Ruffolo, D.; Matthaeus, W. H.; Chuychai, P.

2010-01-01

In recent observations by the Advanced Composition Explorer, the intensity of solar energetic particles exhibits sudden, large changes known as dropouts. These have been explained in terms of turbulence or a flux tube structure in the solar wind. Dropouts are believed to indicate filamentary magnetic connection to a localized particle source near the solar surface, and computer simulations of a random-phase model of magnetic turbulence have indicated a spatial association between dropout features and local trapping boundaries (LTBs) defined for a two-dimensional (2D) + slab model of turbulence. Previous observations have shown that dropout features are not well associated with sharp magnetic field changes, as might be expected in the flux tube model. Random-phase turbulence models do not properly treat sharp changes in the magnetic field, such as current sheets, and thus cannot be tested in this way. Here, we explore the properties of a more realistic magnetohydrodynamic (MHD) turbulence model (2D MHD), in which current sheets develop and the current and magnetic field have characteristic non-Gaussian statistical properties. For this model, computer simulations that trace field lines to determine magnetic connection from a localized particle source indicate that sharp particle gradients should frequently be associated with LTBs, sometimes with strong 2D magnetic fluctuations, and infrequently with current sheets. Thus, the 2D MHD + slab model of turbulent fluctuations includes some realistic features of the flux tube view and is consistent with the lack of an observed association between dropouts and intense magnetic fields or currents.

Transport currents along c-axis and (a,b) planes in YBCO single domain materials. Critical current densities and normal-superconducting transitions

International Nuclear Information System (INIS)

Porcar, L.; Bourgault, D.; Chaud, X.; Noudem, J.G.; Tournier, R.; Tixador, P.

1998-01-01

High transport currents along the (a,b) planes and along the c-axis have been measured in pulsed current of different pseudo-frequencies. Self field losses and transport current of 8000 A (20000 A cm -2 ) have been measured in Y 1 Ba 2 Cu 3 O 7-δ bars textured by the melting zone technique. Critical currents as high as 500 A (90000 A cm -2 ) along the (a,b) planes or 3000 A (7500 A cm -2 ) along the c-axis have been measured. For both orientations, the transition from the normal state to the superconducting state has been observed. Electric field of 1000 V m -1 and study of the superconducting state recovery are reported. (orig.)

Forces of vortice trapping and critical current in type II superconductors

International Nuclear Information System (INIS)

Bormio, C.

1985-12-01

The vortice-centers interactions of trapping in type II superconductor materials were studied by two theories: thermodynamic (Hampshire-Taylor) and microscopic (Larkin - Ovchinnikov). The study was applied to NbTi with composition of 50% weight of Ti. They are commercial cables containing 361 filaments with final diameter of 0.35 mm for the wire and 9.2 μm foi filaments. The material presents high deformation rate in area and high density of dislocations. These defects actuate as centers of trapping. Variations in themomechanical treatments of superconductor cables modify the interaction mechanisms. The specific mechanism for each treatment type was identified. Measurements of critical current density in function of magnetic field in the range from 1 to 7 Tesla were done, which the usual superconductor parameters as upper critical field and Ginzburg - Landau (Kappa-k) parameter are estimated from literature data. (M.C.K.) [pt

Self-field AC losses and critical currents in multi-tube Ag-Bi-2223 conductors

Energy Technology Data Exchange (ETDEWEB)

Ciszek, M; Ashworth, S P; Campbell, A M [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); James, M P; Glowacki, B A [IRC in Superconductivity, University of Cambridge, Madingley Road, Cambridge CB3 0HE (United Kingdom); Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ (United Kingdom); Garre, R; Conti, S [Centro Ricerche Europa Metalli, Fornaci di Barga, LU (Italy)

1996-05-01

The purpose of this work was to investigate the influence of different technological treatments of silver sheathed Bi-2223 tapes on the critical current density and the AC transport losses. The tapes were produced using the 'tube-in-tube' technique, by including a silver rod in the centre of the superconducting powder during packing of the silver tube. The aim of the process is to increase the silver to superconductor surface area and thus also the alignment at the centre of the conductor ceramic core. AC transport losses were measured by means of an electrical method using sinusoidally varying currents in the frequency range 30-180 Hz. In this range the power losses are hysteretic. The measured variation in losses from those predicted by a critical state model is attributed to the complex geometry of superconducting regions existing in these tapes. (author)

Uniaxial Strain Induced Critical Current Degradation of Ag-Sheathed Bi-2212 Round Wire

NARCIS (Netherlands)

Dai, Chao; Qin, Jinggang; Liu, Bo; Liu, Peihang; Wu, Yu; Nijhuis, Arend; Zhou, Chao; Li, Chenshan; Hao, Qingbin; Liu, Sheng

2018-01-01

The critical current degradation of Bi-2212 Ag-sheathed round wire subjected to uniaxial strain was studied at 4.2 K in 14 T background field. The strains applied on the sample are both tension and compression. The additional tensile strain caused by the difference in thermal expansion between the

Microstructural and crystallographic imperfections of MgB{sub 2} superconducting wire and their correlation with the critical current density

Energy Technology Data Exchange (ETDEWEB)

Shahabuddin, Mohammed; Alzayed, Nasser S. [Department of Physics and Astronomy, College of Science, P. O. Box 2455, King Saud University, Riyadh 11451 (Saudi Arabia); Oh, Sangjun [Materials Research Team, National Fusion Research Institute, Yueeong, Daejeon 305-333 (Korea, Republic of); Choi, Seyong [Busan Center, Korea Basic Science Institute, Geumjeong, Busan 609-735 (Korea, Republic of); Maeda, Minoru [Department of Physics, College of Science and Technology, Nihon University, 1-8 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8308 (Japan); Hata, Satoshi; Shimada, Yusuke [Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580 (Japan); Hossain, Md Shahriar Al [Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia); Kim, Jung Ho, E-mail: jhk@uow.edu.au [Department of Physics and Astronomy, College of Science, P. O. Box 2455, King Saud University, Riyadh 11451 (Saudi Arabia); Institute for Superconducting and Electronic Materials, University of Wollongong, North Wollongong, New South Wales 2500 (Australia)

2014-01-15

A comprehensive study of the effects of structural imperfections in MgB{sub 2} superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB{sub 2} material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB{sub 2}, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB{sub 2}, however, even at low sintering temperature, and thus block current transport paths.

The critical current of point symmetric Josephson tunnel junctions

International Nuclear Information System (INIS)

Monaco, Roberto

2016-01-01

Highlights: • We disclose some geometrical properties of the critical current field dependence that apply to a large class of Josephson junctions characterized by a point symmetric shape. • The developed theory is valid for any orientation of the applied magnetic field, therefore it allows the determine the consequences of field misalignment in the experimental setups. • We also address that the threshold curves of Josephson tunnel junctions with complex shapes can be expressed as a linear combination of the threshold curves of junctions with simpler point symmetric shapes. - Abstract: The physics of Josephson tunnel junctions drastically depends on their geometrical configurations. The shape of the junction determines the specific form of the magnetic-field dependence of its Josephson current. Here we address the magnetic diffraction patterns of specially shaped planar Josephson tunnel junctions in the presence of an in-plane magnetic field of arbitrary orientations. We focus on a wide ensemble of junctions whose shape is invariant under point reflection. We analyze the implications of this type of isometry and derive the threshold curves of junctions whose shape is the union or the relative complement of two point symmetric plane figures.

Critical Current Properties of HTS Twisted Stacked-Tape Cable in Subcooled- and Pressurized-Liquid Nitrogen

International Nuclear Information System (INIS)

Tomita, M; Suzuki, K; Fukumoto, Y; Ishihara, A; Akasaka, T; Kobayashi, Y; Maeda, A; Takayasu, M

2015-01-01

A 2 m length Twisted Stacked-Tape Cable (TSTC) conductor which was fabricated by 32-YBCO-tapes (4 mm width) with a 200 mm twist pitch was investigated at various temperatures near 77 K in subcooled- and pressurized-liquid nitrogen. The critical current of the TSTC cable which was 1.45 kA at 77 K measured from 64 K to 85 K by controlling the equilibrium vapor pressure of nitrogen bath and were varied from 3.65 kA at 64 K to 0.42 kA at 85 K. The temperature dependence of cables’ critical current agrees with that of the 4 mm width YBCO tape. These results are encouraging for applications of a compact Twisted Stacked-Tape Cable application in railway systems. (paper)

Critical current and flux dynamics in Ag-doped FeSe superconductor

Science.gov (United States)

Galluzzi, A.; Polichetti, M.; Buchkov, K.; Nazarova, E.; Mancusi, D.; Pace, S.

2017-02-01

The measurements of DC magnetization as a function of the temperature M(T), magnetic field M(H), and time M(t) have been performed in order to compare the superconducting and pinning properties of an undoped FeSe0.94 sample and a silver doped FeSe0.94 + 6 wt% Ag sample. The M(T) curves indicate an improvement of the superconducting critical temperature and a reduction of the non-superconducting phase Fe7Se8 due to the silver doping. This is confirmed by the field and temperature dependent critical current density Jc(H,T) extracted from the superconducting hysteresis loops at different temperatures within the Bean critical state model. Moreover, the combined analysis of the Jc(T) and of the pinning force Fp(H/Hirr) indicate that the pinning mechanisms in both samples can be described in the framework of the collective pinning theory. The U*(T, J) curves show a pinning crossover from an elastic creep regime of intermediate size flux bundles, for low temperatures, to a plastic creep regime at higher temperatures for both the samples. Finally, the vortex hopping attempt time has been evaluated for both samples and the results are comparable with the values reported in the literature for high Tc materials.

Critical currents and energy dissipation in Y1Ba2Cu3O7-δ films

International Nuclear Information System (INIS)

Windte, C.V.

1993-09-01

The critical current density j c of patterned YBaCuO thin film samples and the electric field E seen by the superconductor were calculated from data of magnetization loops, external magnetic field sweeps and relaxation, respectively. Data were taken at 77 K up to external magnetic fields of 150 mT with a sensitive Hall probe detecting the magnetic fields of the screening currents of the sample. The E(j) characteristic could be determined over six decades of magnitude of E (10 -7 μV/cm -1 μV/cm). These characteristics permit the comparison with theoretical pictures: They are incompatible with Kim-Andersons flux-creep and a power law behaviour. The characteristics are compatible with the vortex-glass or the collective pinning ansatz. There exists a limiting critical current beyond no known theoretical picture describes the E(j) characteristic. (orig.) [de

Influence of Electrolyte Modulus on the Local Current Density at a Dendrite Tip on a Lithium Metal Electrode

Energy Technology Data Exchange (ETDEWEB)

Harry, KJ; Higa, K; Srinivasan, V; Balsara, NP

2016-08-10

Understanding and controlling the electrochemical deposition of lithium is imperative for the safe use of rechargeable batteries with a lithium metal anode. Solid block copolymer electrolyte membranes are known to enhance the stability of lithium metal anodes by mechanically suppressing the formation of lithium protrusions during battery charging. Time-resolved hard X-ray microtomography was used to monitor the internal structure of a symmetric lithium-polymer cell during galvanostatic polarization. The microtomography images were used to determine the local rate of lithium deposition, i.e. local current density, in the vicinity of a lithium globule growing through the electrolyte. Measurements of electrolyte displacement enabled estimation of local stresses in the electrolyte. At early times, the current density was maximized at the globule tip, as expected from simple current distribution arguments. At later times, the current density was maximized at the globule perimeter. We show that this phenomenon is related to the local stress fields that arise as the electrolyte is deformed. The local current density, normalized for the radius of curvature, decreases with increasing compressive stresses at the lithium-polymer interface. To our knowledge, our study provides the first direct measurement showing the influence of local mechanical stresses on the deposition kinetics at lithium metal electrodes.

Improvements in the critical current densities of Nb3Sn by solid solution additions of Sn in Nb

International Nuclear Information System (INIS)

Luhman, T.; Suenaga, M.

1975-01-01

The effectiveness of solid solution additions of Sn to Nb in improving the superconducting properties of diffusion processed Nb 3 Sn conductors was examined. It was found that an increase in the superconducting critical current density, Jc, as function of layer thickness (d) may be obtained for thick Nb 3 Sn layers by solid solution additions of Sn in Nb. A large increase in J/sub c/ (d) is also achieved by increasing the Sn content in the bronze matrix material. In addition to uses of this material in magnet fabrications a potential application of these improved J/sub c/(d) values may lie in the use of Nb 3 Sn in power transmission lines. Here, a high superconducting critical current density is necessary throughout the material to carry the increased current during fault conditions. The magnetic field dependence of J/sub c/ is a function of alloy content but the alloying changes studied here do not increase the high field critical current capability of Nb 3 Sn. (auth)

Localized Induced Current Stimulation to Neuronal Culture Using Soft Magnetic Material

Science.gov (United States)

Saito, Atsushi; Saito, Aki; Moriguchi, Hiroyuki; Kotani, Kiyoshi; Jimbo, Yasuhiko

To establish precisely focused magnetic stimulation, we developed a Mu-meal based low-frequency localized induced current (LIC) stimulation system with micro-fabricated dual cell-culture chamber. The dual cell-culture chamber was arranged in a concentric circle manner. Between the inner and outer chambers, 4 or 8 connecting micro-channels were fabricated using polydimethylsiloxane (PDMS). Rat cortical neurons were separately cultured in outer and inner chambers. Through the micro-channels, functional synaptic connections were formed. Mu-metal that has very high magnetic permeability was aligned along the outer circle, which allowed us of LIC stimulation to the cells in the outer chamber. Applying low-frequency magnetic fields to the Mu-metal, induced currents were generated and the electrical activity of the cells in the outer chamber was modified depending on the stimulation intensity. Following the modified activity in the outer circles, the cells in the inner chamber also showed slightly depressed activity patterns. These results suggested that our system would be promising for localized stimulation of neuronal networks and highly regulation of network activities.

Enhancement of critical current density of in situ processed MgB sub 2 tapes by WB addition

CERN Document Server

Fujii, H; Kumakura, H

2003-01-01

The effect of tungsten boride (WB) addition on the microstructure and superconducting properties of Fe-sheathed MgB sub 2 tapes has been investigated. The microstructure was not influenced appreciably by the addition, whereas the superconducting properties changed. Even by a 5 mol% addition, the critical temperature (T sub c) decreased by about 0.5 K. However, the field dependence of the inductive critical current density (J sub c sub i) became smaller with the increase in the amount of addition, suggesting that pinning centres effective in a high-field region were possibly introduced. The transport critical current density (J sub c sub t) at 4.2 K increased about twice by the 5 mol% addition and reached 15 and 5 kA cm sup - sup 2 at 8 and 10 T, respectively.

Casimir amplitudes and capillary condensation of near-critical fluids between parallel plates: renormalized local functional theory.

Science.gov (United States)

Okamoto, Ryuichi; Onuki, Akira

2012-03-21

We investigate the critical behavior of a near-critical fluid confined between two parallel plates in contact with a reservoir by calculating the order parameter profile and the Casimir amplitudes (for the force density and for the grand potential). Our results are applicable to one-component fluids and binary mixtures. We assume that the walls absorb one of the fluid components selectively for binary mixtures. We propose a renormalized local functional theory accounting for the fluctuation effects. Analysis is performed in the plane of the temperature T and the order parameter in the reservoir ψ(∞). Our theory is universal if the physical quantities are scaled appropriately. If the component favored by the walls is slightly poor in the reservoir, there appears a line of first-order phase transition of capillary condensation outside the bulk coexistence curve. The excess adsorption changes discontinuously between condensed and noncondensed states at the transition. With increasing T, the transition line ends at a capillary critical point T=T(c) (ca) slightly lower than the bulk critical temperature T(c) for the upper critical solution temperature. The Casimir amplitudes are larger than their critical point values by 10-100 times at off-critical compositions near the capillary condensation line. © 2012 American Institute of Physics

Dislocation structure, aging processes and critical currents of vanadium-gallium alloys

International Nuclear Information System (INIS)

Pan, V.M.; Beletskii, Yu.I.; Flis, V.S.; Firstov, S.A.; Sarzhan, G.F.

1976-04-01

An electron microscopical investigation of the structural and phase changes in vanadium-gallium alloys was carried out in the range of concentrations corresponding to a supersaturated mixed crystal with bcc lattice during plastic deformation and annealing. The determined data were compared with the measured results of the electrophysical and superconducting properties. It was shown that the deformed and aged vanadium-gallium samples at 4.2 K could conduct a dissipation-free transport current with a density of 8 x 10 3 A/cm 2 in the transversal magnetic field of 60 kOe. Based on the experimental results of the dislocation structure, the mechanism and kinetics of the separation process, conclusions were drawn as to the character of the exceeding of the critical current density in the presence of a magnetic field in these compounds. (orig.) [de

Uranium doping and neutron irradiation of Bi-2223 superconduction tapes for improved critical current density

International Nuclear Information System (INIS)

Moss, S.D.; Wang, W.G.; Dou, S.X.; Weinstein, R.

1998-01-01

It is demonstrated that a combination of neutron irradiation with uranium doping introduce fission tracks through a Bi-2223 tape which act as effective pinning centres, leading to a substantial increase in critical current. Preliminary data suggests that the combination of uranium doping and neutron irradiation produces improved flux pinning in Bi-2223 tapes over neutron irradiation alone. Before irradiation, SEM, DTA and XRD analyses were performed on the tapes. Both before and after irradiation the trapped maximum magnetic flux was measured at 77K. Before neutron irradiation, uranium doping has no effect on critical current. Preliminary SEM data suggested that the uranium is homogeneously distributed throughout the oxide core of the tape. The presence of 2212 and other secondary phases in the doped tapes suggest further refinement of the sintering procedure is necessary. (authors)

Critical current densities amd pinning mechanisms of high-Tc films on single crystalline and technologically relevant substrates. Final report

International Nuclear Information System (INIS)

Adrian, H.

1995-12-01

The report deals with six project tasks: (1) Effects of impurity additions at atomic level on the pinning behaviour and the critical current densities, examined in epitactic YBA 2 (Cu 1-x Ni x ) 3 O 7 films. It could be proven that the Ni atoms increase the activation energy for flux movement and the critical current density in a concentration range of 0 2 Sr 2 Ca n-1 Cu n O 2n+4+δ films (n = 2 and 3) with good crystalline properties, high critical currents, and high current densities were prepared. Thin YBa 2 Cu 3 O 7 films of high quality could be grown on saphire substrates, both by the MO-CVD process and by MBE. The aim of depositing biaxially textured YBa 2 Cu 3 O 7 films with high critical current densities on polycrystalline, metallic substrates was achieved by the IBAD process combined with MBE. The buffer layer was YSZ. Heterostructures of the layer sequence YBa 2 Cu 3 O 7 /CeO 2 /Y 0.3 Pr 0.7 Ba 2 Cu 3 O 7 /YBa 2 Cu 3 O 7 and YBa 2 Cu 3 O 7 /CeO 2 /Au were prepared by laser ablation and sputtering processes, in order to examine Josephson ramp contacts and superconducting field-effect transistors. (orig./MM) [de

Local Magnetic Measurements of Trapped Flux Through a Permanent Current Path in Graphite

Science.gov (United States)

Stiller, Markus; Esquinazi, Pablo D.; Quiquia, José Barzola; Precker, Christian E.

2018-04-01

Temperature- and field-dependent measurements of the electrical resistance of different natural graphite samples suggest the existence of superconductivity at room temperature in some regions of the samples. To verify whether dissipationless electrical currents are responsible for the trapped magnetic flux inferred from electrical resistance measurements, we localized them using magnetic force microscopy on a natural graphite sample in remanent state after applying a magnetic field. The obtained evidence indicates that at room temperature a permanent current flows at the border of the trapped flux region. The current path vanishes at the same transition temperature T_c≈ 370 K as the one obtained from electrical resistance measurements on the same sample. This sudden decrease in the phase is different from what is expected for a ferromagnetic material. Time-dependent measurements of the signal show the typical behavior of flux creep of a permanent current flowing in a superconductor. The overall results support the existence of room-temperature superconductivity at certain regions in the graphite structure and indicate that magnetic force microscopy is suitable to localize them. Magnetic coupling is excluded as origin of the observed phase signal.

An exponential scaling law for the strain dependence of the Nb3Sn critical current density

International Nuclear Information System (INIS)

Bordini, B; Alknes, P; Bottura, L; Rossi, L; Valentinis, D

2013-01-01

The critical current density of the Nb 3 Sn superconductor is strongly dependent on the strain applied to the material. In order to investigate this dependence, it is a common practice to measure the critical current of Nb 3 Sn strands for different values of applied axial strain. In the literature, several models have been proposed to describe these experimental data in the reversible strain region. All these models are capable of fitting the measurement results in the strain region where data are collected, but tend to predict unphysical trends outside the range of data, and especially for large strain values. In this paper we present a model of a new strain function, together with the results obtained by applying the new scaling law on relevant datasets. The data analyzed consisted of the critical current measurements at 4.2 K that were carried out under applied axial strain at Durham University and the University of Geneva on different strand types. With respect to the previous models proposed, the new scaling function does not present problems at large strain values, has a lower number of fitting parameters (only two instead of three or four), and is very stable, so that, starting from few experimental points, it can estimate quite accurately the strand behavior in a strain region where there are no data. A relationship is shown between the proposed strain function and the elastic strain energy, and an analogy is drawn with the exponential form of the McMillan equation for the critical temperature. (paper)

Critical current density of MgB2 thin films and the effect of interface pinning

International Nuclear Information System (INIS)

Choi, Eun-Mi; Gupta, S K; Sen, Shashwati; Lee, Hyun-Sook; Kim, Hyun-Jung; Lee, Sung-Ik

2004-01-01

Preferentially oriented MgB 2 thin films with c-axis normal to the surface have been prepared and characterized for microstructure and transport properties. The magnetic field dependence of superconducting critical current density J c has been determined from the magnetization hysteresis (M-H) loops at various temperatures using the Bean's critical state model. High J c of these films show their potential for applications. We have also measured the angular dependences of J c . The angular dependence is seen to be in agreement with the anisotropic Ginzburg-Landau model except that at angles close to the ab plane, increased pinning due to film-substrate interaction is observed. The angular range where interface pinning is effective has been determined by measurement of asymmetry in dissipation on reversal of current for fields applied at angles close to the ab plane

Effect of eddy current damping on phononic band gaps generated by locally resonant periodic structures

Science.gov (United States)

Ozkaya, Efe; Yilmaz, Cetin

2017-02-01

The effect of eddy current damping on a novel locally resonant periodic structure is investigated. The frequency response characteristics are obtained by using a lumped parameter and a finite element model. In order to obtain wide band gaps at low frequencies, the periodic structure is optimized according to certain constraints, such as mass distribution in the unit cell, lower limit of the band gap, stiffness between the components in the unit cell, the size of magnets used for eddy current damping, and the number of unit cells in the periodic structure. Then, the locally resonant periodic structure with eddy current damping is manufactured and its experimental frequency response is obtained. The frequency response results obtained analytically, numerically and experimentally match quite well. The inclusion of eddy current damping to the periodic structure decreases amplitudes of resonance peaks without disturbing stop band width.

Analysis of the ac SQUID with low inductance and low critical current

DEFF Research Database (Denmark)

Sørensen, O. H.

1976-01-01

The properties of the ac SQUID magnetometer has been analyzed. The results are valid in the low-inductance low-critical-current regime, where the Lri0 producted is belowthe value at which the relation between the enclosed and externally applied magnetic dc flux becomes reentrant. The effects...... of the screening current circulating in the SQUID ring as well as of the SQUID-ring time constant, tau-Lr/R9 are taken into account. Here LR IS THE SQUID-ring inductance, and R is the shunt resistance in the shunted junction model assumed to describe the weak link. It is shown that for finite values of omegatau...... constriuctively with the result that the optimal response occurs at a definite and finite value of omegatau. If omegatau is increased beyond this optimal value the weak link behavior is dominated by the Ohmic current channel implying that only if the shunt conductance contains a term depending...

[Team approaches to critical bleeding (massive bleeding and transfusion) - chairmen's introductory remarks. Questionnaire survey on current status of hospital clinical laboratories evaluating critical hemorrhage].

Science.gov (United States)

Kino, Shuichi; Suwabe, Akira

2014-12-01

In 2007, "the Guidelines for Actions against Intraoperative Critical Hemorrhage" were established by the Japanese Society of Anaesthesiologists and the Japanese Society of Blood transfusion and Cell Therapy. The documentation of in-hospital procedures for critical hemorrhage, especially about how to select RBC units, has widely standardized hospital practice. Patients with intraoperative critical hemorrhage sometimes suffer from massive blood loss. In this situation, some patients develop coagulopathy. To treat them, we need to evaluate their coagulation status based on laboratory test results. So, we performed a nationwide questionnaire survey on the current status of hospital clinical laboratories evaluating critical hemorrhage. From the results of this survey, it was recommended that central hospital laboratories should try to reduce the turn-around time required to test for coagulation parameters as much as possible for appropriate substitution therapy. (Review).

Neutron radiography characterization of an operating proton exchange membrane fuel cell with localized current distribution measurements

International Nuclear Information System (INIS)

Gagliardo, J.J.; Owejan, J.P.; Trabold, T.A.; Tighe, T.W.

2009-01-01

Neutron radiography has proven to be a powerful tool to study and understand the effects of liquid water in an operating fuel cell. In the present work, this experimental method is coupled with locally resolved current and ohmic resistance measurements, giving additional insight into water management and fuel cell performance under a variety of conditions. The effects of varying the inlet humidification level and the current density of the 50 cm 2 cell are studied by simultaneously monitoring electrochemical performance with a 10x10 matrix of current sensors, and liquid water volumes are measured using the National Institute of Standards and Technology (NIST) neutron imaging facility. A counter flow, straight channel proton exchange membrane (PEM) fuel cell is used to demonstrate localized performance loss corresponds to water-filled channels that impede gas transport to the catalyst layer, thereby creating an area that has low current density. Furthermore, certain operating conditions causing excess water accumulation in the channels can result in localized proton resistance increase, a result that can only be accurately observed with combined radiography and distributed electrochemical measurements.

Effects of oxygen content on the pinning energy and critical current in the granular (Hg, Re)-1223 superconductors

International Nuclear Information System (INIS)

Passos, C.A.C.; Orlando, M.T.D.; Fernandes, A.A.R.; Oliveira, F.D.C.; Simonetti, D.S.L.; Fardin, J.F.; Belich, H.; Ferreira, M.M.

2005-01-01

Hg 0.82 Re 0.18 Ba 2 Ca 2 Cu 3 O 8+d polycrystalline samples, with different oxygen content, were investigated by ac resistance measurements under different applied magnetic field (up to 3 A/m) and critical current measurements. The intergrain and intragrain regions have shown an improvement in the pinning energy and critical current density, as considering the precursor preparation with 10% of O 2 and 90% of Ar (optimal doped). In addition, the samples presented S-I-S junctions type as considering Ambegaokar-Baratoff theory

Study of local currents in low dimension materials using complex injecting potentials

Science.gov (United States)

He, Shenglai; Covington, Cody; Varga, Kálmán

2018-04-01

A complex potential is constructed to inject electrons into the conduction band, mimicking electron currents in nanoscale systems. The injected electrons are time propagated until a steady state is reached. The local current density can then be calculated to show the path of the conducting electrons on an atomistic level. The method allows for the calculation of the current density vectors within the medium as a function of energy of the conducting electron. Using this method, we investigate the electron pathway of graphene nanoribbons in various structures, molecular junctions, and black phosphorus nanoribbons. By analyzing the current flow through the structures, we find strong dependence on the structural geometry and the energy of the injected electrons. This method may be of general use in the study of nano-electronic materials and interfaces.

Critical current degradation of short YBa2Cu3O7-δ coated conductor due to an unprotected quench

International Nuclear Information System (INIS)

Wang, X; Trociewitz, U P; Schwartz, J

2011-01-01

The critical current of a short YBa 2 Cu 3 O 7-δ (YBCO) coated conductor sample degrades in an unprotected quench performed in a nearly adiabatic environment at 30 K. The conductor has Cu stabilizers on both surfaces. The quench is initiated by a heater attached to the sample surface. The amplitude of the transport current is fixed as 91% of the sample's initial critical current. The duration of the current is increased to simulate an unprotected quench and to reach increasing and controlled voltage and temperature levels. A peak temperature of 490 ± 50 K and a heating rate of 1800 K s -1 are measured when the critical current degrades by ∼ 5%. The applied thermal strain on the YBCO layer from 30 to 490 K is estimated to be 0.31% and is applied at a strain rate of ∼ 1% s -1 . The rate of temperature change and the time to reach a certain peak temperature, determined by the current density in the Cu stabilizer, are estimated assuming adiabatic conditions based on the short sample case. For a Cu stabilizer current density ranging from 1000 to 2000 A mm -2 , achieved in commercial conductors currently available, the quench detection and protection requires a response time -2 may challenge the existing detection and protection techniques for the same 200 K limit. Integrating the substrate as part of the stabilizer may help reduce the stabilizer current density to gain more time for quench detection and protection while maintaining the engineering current density.

First time observation of local current shrinkage during the MARFE behavior on the J-TEXT tokamak

Science.gov (United States)

Shi, Peng; Zhuang, G.; Gentle, K.; Hu, Qiming; Chen, Jie; Li, Qiang; Liu, Yang; Gao, Li; Zhang, Xiaolong; Liu, Hai; Chen, Zhipeng; Zhu, Lizhi; Li, Fuming; Zhou, Yinan; Zeng, Zhong; Liu, Linzi; He, Jiyang

2017-11-01

Multifaceted asymmetric radiation as well as strong poloidal asymmetry of the electron density from the edge, dubbed as ‘MARFE’, has been observed in high electron density Ohmically heated plasmas on J-TEXT tokamak. Equilibrium reconstruction based on the measured data from the 17-channel FIR polarimeter-interferometer indicates that an asymmetric plasma current density distribution forms at the edge region and the plasma current shrinkage locates at the MARFE affected region. Furthermore, associated with the localized plasma current shrinkage, a locked mode MHD activity is excited, which then terminate the discharge with a major disruption. Localized plasma current shrinkage at the MARFE region is considered to be the direct cause for the density limit disruptions, and the proposed interpretation is consistent with the experimental observations.

Improved critical current of YBaCuO thick-films and ceramics by the addition of Ag

International Nuclear Information System (INIS)

Dwir, B.; Kellett, B.; Mieville, L.; Pavuna, D.

1991-01-01

In a series of papers we have discussed the importance of Ag for contacts and analyzed the resistivity, magnetization, critical current density and percolation properties of YBCO-Ag ceramics. This work has been followed by investigation of electrical and structural properties of thick-films containing Ag in their composition. Here we summarize the most important of our results: In YBCO-Ag ceramic compounds, silver fills the intergranular space (voids), improving the YBaCuO compactness and enhancing the critical current density. These properties are mostly enhanced at 10-20% wt% Ag. The reduction in normal-state resistivity can be described well by 3D percolation theory with a critical concentration of ≅20%. In thick films, prepared by spinning YBaCuO powders on a substrate, adding silver (in the form of Ag 2 O) to the powder mixture improves both T c and J c (by up to 50%), as well as resistivity and resistivity slope. The structural properties, like amount of secondary phases and micro-crack density, are also improved by the addition of Ag. (orig.)

Experimental investigation of localized stress-induced leakage current distribution in gate dielectrics using array test circuit

Science.gov (United States)

Park, Hyeonwoo; Teramoto, Akinobu; Kuroda, Rihito; Suwa, Tomoyuki; Sugawa, Shigetoshi

2018-04-01

Localized stress-induced leakage current (SILC) has become a major problem in the reliability of flash memories. To reduce it, clarifying the SILC mechanism is important, and statistical measurement and analysis have to be carried out. In this study, we applied an array test circuit that can measure the SILC distribution of more than 80,000 nMOSFETs with various gate areas at a high speed (within 80 s) and a high accuracy (on the 10-17 A current order). The results clarified that the distributions of localized SILC in different gate areas follow a universal distribution assuming the same SILC defect density distribution per unit area, and the current of localized SILC defects does not scale down with the gate area. Moreover, the distribution of SILC defect density and its dependence on the oxide field for measurement (E OX-Measure) were experimentally determined for fabricated devices.

Limits to the critical transport current in superconducting (Bi,Pb)2Sr2Ca2Cu3O10 silver-sheathed tapes: The railway-switch model

International Nuclear Information System (INIS)

Hensel, B.; Grasso, G.; Fluekiger, R.

1995-01-01

We have proposed the ''railway-switch'' model to describe the superconducting transport current in (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10 silver-sheathed tapes. The model assumes that in the textured polycrystalline filament the frequent small-angle c-axis tilt grain boundaries (''railway switches'') constitute strong links for the supercurrent. With the objective to identify the mechanisms that limit the critical-current density in the tapes we present measurements of the transport critical current normal to the tape plane and of the current-transfer length along the tape axis. From I-V curves we obtain the longitudinal critical-current distribution and compare it to the thickness variation of the filament. The experiments have been performed on monofilamentary powder-in-tube samples prepared in long lengths by rolling as the only tape-forming process. For all investigated samples the critical-current density at T=77 K in self-field was in the range j c =20--30 kA/cm 2 . We conclude that the dominant limitation for the transport critical current in the tapes is imposed by the low intragrain critical-current density j c c along the c axis (as compared to the in-plane critical-current density j c ab ) and by the even lower critical-current density j c t across twist boundaries or intergrowths. Possibilities for an improvement of the performance of the (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10 silver-sheathed tapes are discussed

Current clinical nutrition practices in critically ill patients in Latin America: a multinational observational study.

Science.gov (United States)

Vallejo, Karin Papapietro; Martínez, Carolina Méndez; Matos Adames, Alfredo A; Fuchs-Tarlovsky, Vanessa; Nogales, Guillermo Carlos Contreras; Paz, Roger Enrique Riofrio; Perman, Mario Ignacio; Correia, Maria Isabel Toulson Davisson; Waitzberg, Dan Linetzky

2017-08-25

Malnutrition in critically ill adults in the intensive care unit (ICU) is associated with a significantly elevated risk of mortality. Adequate nutrition therapy is crucial to optimise outcomes. Currently, there is a paucity of such data in Latin America. Our aims were to characterise current clinical nutrition practices in the ICU setting in Latin America and evaluate whether current practices meet caloric and protein requirements in critically ill patients receiving nutrition therapy. We conducted a cross-sectional, retrospective, observational study in eight Latin American countries (Argentina, Brazil, Chile, Colombia, Ecuador, Mexico, Panama, and Peru). Eligible patients were critically ill adults hospitalised in the ICU and receiving enteral nutrition (EN) and/or parenteral nutrition (PN) on the Screening Day and the previous day (day -1). Caloric and protein balance on day -1, nutritional status, and prescribed nutrition therapy were recorded. Multivariable logistic regression analysis was performed to identify independent predictors of reaching daily caloric and protein targets. The analysis included 1053 patients from 116 hospitals. Evaluation of nutritional status showed that 74.1% of patients had suspected/moderate or severe malnutrition according to the Subjective Global Assessment. Prescribed nutrition therapy included EN alone (79.9%), PN alone (9.4%), and EN + PN (10.7%). Caloric intake met >90% of the daily target in 59.7% of patients on day -1; a caloric deficit was present in 40.3%, with a mean (±SD) daily caloric deficit of -688.8 ± 455.2 kcal. Multivariable logistic regression analysis showed that combined administration of EN + PN was associated with a statistically significant increase in the probability of meeting >90% of daily caloric and protein targets compared with EN alone (odds ratio, 1.56; 95% confidence interval, 1.02-2.39; p = 0.038). In the ICU setting in Latin America, malnutrition was highly prevalent and caloric

Critical current oscillations in superconductor-ferromagnet-superconductor structure taking into account s-d scattering

International Nuclear Information System (INIS)

Vedyaev, A.V.; Ryzhanova, N.V.; Pugach, N.G.

2007-01-01

One calculated the critical current in the Josephson contact with the transition metal slightly ferromagnetic alloy interlayer. One solved the Gorkov equations taking into account s-d-scattering in a ferromagnet. The account of the mentioned scattering breaking down the Cooper pairs is shown to enable to ensure the conformity with the experiment [ru

Development of high temperature superconductors having high critical current density

International Nuclear Information System (INIS)

Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H.

2000-08-01

Fabrication of high T c superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm 2 and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation

Development of high temperature superconductors having high critical current density

Energy Technology Data Exchange (ETDEWEB)

Hong, Gye Wong; Kim, C. J.; Lee, H.G.; Kwon, S. C.; Lee, H. J.; Kim, K. B.; Park, J. Y.; Jung, C. H

2000-08-01

Fabrication of high T{sub c} superconductors and its applications for electric power device were carried out for developing superconductor application technologies. High quality YBCO superconductors was fabricated by melt texture growth, top-seeded melt growth process and multi-seeded melt growth process and the properties was compared. The critical current density of the melt processed YBCO superconductors was about few 10,000 A/cm{sup 2} and the levitation force was 50 N. The processing time needed for the growth of the 123 single grain was greatly reduced by applying multi-seeding without no significant degradation of the levitation force. The multi-seeded melt growth process was confirmed as a time-saving and cost-effective method for the fabrication of bulk superconductors with controlled crystallographic orientation.

Effect of copper additions in tin molten pool on stability temperature and critical current of Nb3Sn

International Nuclear Information System (INIS)

Kruzliak, J.; Hutka, P.; Tomasich, M.

1979-01-01

Tested is the effect of 55 at% copper addition into the tin bath on the stability temperature and crytical current of Nb 3 Sn, prepared by the diffusion method. It is shown that copper presence in the tin bath transfers the stability temperature of NbSn 2 and Nb 6 Sn 5 phases below the annealing temperature of 700 deg C. It results in Nb 3 Sn appearance at the annealing temperatures above 600 deg C. The critical current increase is explained as follows: lower Nb 3 Sn appearance temperatures provide fine-grained structure of superconducting Nb 3 Sn layer with greater density of binning centers and with higher critical current in accordance with NbSn prepared by the diffusion of pure tin into niobium

Experiment of enhancing critical current and reducing ac loss in pancake coil comprised of Ni-coated Bi-2223/Ag tape

International Nuclear Information System (INIS)

Alamgir, A.K.M.; Gu, C.; Han, Z.

2006-01-01

An approach of realizing high performance HTS coil comprised of ferromagnetic material-coated BSCCO tape is proposed. The concept of influencing critical current and ac loss is based on the magnetic shielding effect resulting in redirection of self-field flux-lines. In the previous article, ac performance of Ni-coated tape was demonstrated where the Ni-coating was introduced at the edge-regime of the finished tape in order to redirect the perpendicular component of self-field lines. In order to investigate the shielding effect on ac performance in HTS coil, a two-turn pancake coil comprised of Ni-coated Bi-2223/Ag tape is demonstrated in the present article. About 6.4% of critical current was enhanced and 30% of transport current ac loss was reduced by means of 40 μm thick and 0.3 mm long (from the edge toward center of the tape) Ni-coating. This result suggests that additional ferromagnetic loss could be compensated well by the shielding effect of the partial Ni-coating. The degree of enhancement in critical current as well as ferromagnetic impact on ac losses depend on the volume and geometry of ferromagnetic coating introduced. Therefore, it is very important to control the parameter of ferromagnetic coating of the tape in order to balance the critical current and ac loss for optimum coil performance

Experiment of enhancing critical current and reducing ac loss in pancake coil comprised of Ni-coated Bi-2223/Ag tape

Energy Technology Data Exchange (ETDEWEB)

Alamgir, A.K.M. [Department of Physics, Applied Superconductivity Research Center, Tsinghua University, Beijing 100084 (China)]. E-mail: alam643@hotmail.com; Gu, C. [Department of Physics, Applied Superconductivity Research Center, Tsinghua University, Beijing 100084 (China); Han, Z. [Department of Physics, Applied Superconductivity Research Center, Tsinghua University, Beijing 100084 (China)

2006-07-01

An approach of realizing high performance HTS coil comprised of ferromagnetic material-coated BSCCO tape is proposed. The concept of influencing critical current and ac loss is based on the magnetic shielding effect resulting in redirection of self-field flux-lines. In the previous article, ac performance of Ni-coated tape was demonstrated where the Ni-coating was introduced at the edge-regime of the finished tape in order to redirect the perpendicular component of self-field lines. In order to investigate the shielding effect on ac performance in HTS coil, a two-turn pancake coil comprised of Ni-coated Bi-2223/Ag tape is demonstrated in the present article. About 6.4% of critical current was enhanced and 30% of transport current ac loss was reduced by means of 40 {mu}m thick and 0.3 mm long (from the edge toward center of the tape) Ni-coating. This result suggests that additional ferromagnetic loss could be compensated well by the shielding effect of the partial Ni-coating. The degree of enhancement in critical current as well as ferromagnetic impact on ac losses depend on the volume and geometry of ferromagnetic coating introduced. Therefore, it is very important to control the parameter of ferromagnetic coating of the tape in order to balance the critical current and ac loss for optimum coil performance.

Views from the Frontline: A critical assessment of local risk governance in South Africa

Directory of Open Access Journals (Sweden)

Doret Botha

2013-02-01

Full Text Available In 2005 the United Nations International Strategy for Disaster Reduction introduced the ‘Hyogo Framework for Action’ (HFA aimed at mainstreaming disaster risk reduction. Subsequently, the ‘Global Network for Disaster Reduction’ (GNDR was formed to support the implementation of the HFA. The GNDR initiated a country-based, international research project called ‘Views from the Frontline’ (VFL in order to measure progress at local level in terms of compliance with the HFA. The VFL 2011 project focused on local risk governance, which is critical for effective implementation of policy and provision of resources at grassroots level. This article provides insight into the findings for South Africa. The project made use of quantitative and qualitative data. Quantitative data was gathered by means of a survey and/or questionnaire consisting of 20 questions on ‘indicators’ which assessed progress toward the goals of the HFA. The surveys also provided for qualitative commentary. The target population for this research consisted of local government officials and community representatives. Based on the quantitative scores for all the different indicators, the research showed that South Africa could still improve significantly in terms of compliance with the HFA. More attention must be given to operationalise the HFA at local level, a culture of safety must be fostered, local actors and communities must be involved directly and consulted, indigenous knowledge must be recognised, and significant capacity development for disaster risk reduction is necessary.

Students' Critical Thinking Skills in Chemistry Learning Using Local Culture-Based 7E Learning Cycle Model

Science.gov (United States)

Suardana, I. Nyoman; Redhana, I. Wayan; Sudiatmika, A. A. Istri Agung Rai; Selamat, I. Nyoman

2018-01-01

This research aimed at describing the effectiveness of the local culture-based 7E learning cycle model in improving students' critical thinking skills in chemistry learning. It was an experimental research with post-test only control group design. The population was the eleventh-grade students of senior high schools in Singaraja, Indonesia. The…

Superconductivity, intergrain, and intragrain critical current densities of materials

International Nuclear Information System (INIS)

Thompson, J.R.; Brynestad, J.; Kroeger, D.M.; Kim, Y.C.; Sekula, S.T.; Christen, D.K.; Specht, E.D.

1989-01-01

Bulk sintered and powdered samples of the high-temperature superconductive compounds Tl 2 Ca 2 Ba 2 Cu 3 O/sub 1+//sub δ/ (Tl-2:2:2:3) and Tl 2 Ca 2 Ba 2 Cu 2 O/sub 8+//sub δ/ (Tl-2:1:2:2) have been synthesized with phase purity of approximately 90%. The materials were characterized by x-ray-diffraction, metallographic, and electron microprobe analyses. The electronic and superconductive properties were investigated through measurement of the electrical resistivity and the critical current density J/sub c/ using transport methods and by extensive magnetization measurements. Primary results and conclusions are that (1) the intragrain J/sub c/ values were large, much larger than the transport values; (2) both sintered and powdered materials exhibited large flux creep; (3) and the J/sub c/ decreased exponentially with temperature. These features are qualitatively very similar to those found in the corresponding YBa 2 Cu 3 O/sub z/ (with z≅7) series of compounds

Temperature and pinning strength dependence of the critical current of a superconductor with a square periodic array of pinning sites

International Nuclear Information System (INIS)

Benkraouda, M.; Obaidat, I.M.; Al Khawaja, U.

2006-01-01

We have conducted extensive series of molecular dynamic simulations on driven vortex lattices interacting with periodic square arrays of pinning sites. In solving the over damped equation of vortex motion we took into account the vortex-vortex repulsion interaction, the attractive vortex-pinning interaction, and the driving Lorentz force at several values of temperature. We have studied the effect of varying the driving Lorentz force and varying the pinning strength on the critical current for several pinning densities, and temperature values. We have found that the pinning strength play an important role in enhancing the critical current over the whole temperature range. At low temperatures, the critical current was found to increase linearly with increasing the pinning strengths for all pinning densities. As the temperature increases, the effect of small pinning strengths diminishes and becomes insignificant at high temperatures

High critical current density YBCO films and fabrication of dc-SQUIDs

CERN Document Server

Kuriki, S; Kawaguchi, Y; Matsuda, M; Otowa, T

2002-01-01

In order to improve the sensitivity of SQUID magnetometers made of high-T sub c films, we have studied the conditions of pulsed-laser deposition of YBCO films. Among the different deposition parameters examined, extensive degassing of the vacuum chamber before and precise control of the substrate temperature during the film deposition were found effective for obtaining high critical temperature T sub c and high critical current density J sub c. It was also found that the residual-resistance ratio has a clear correlation with J sub c , indicating that it can be a good, and easy to measure, index of the film quality. Films having T sub c approx 89-90 K and J sub c >= 5x10 sup 6 A cm sup - sup 2 at 77 K were used to fabricate SQUIDs without a pickup loop. Grain-boundary junctions formed on bicrystal substrates with a 30 deg. misorientation angle exhibited I sub c R sub n values of more than 100 mu V at 77 K. The well-known scaling behaviour of the relation I sub c R sub n propor to (J sup G sup B sub c) sup 1 su...

Overlooked mountain rock pools in deserts are critical local hotspots of biodiversity.

Science.gov (United States)

Vale, Cândida Gomes; Pimm, Stuart L; Brito, José Carlos

2015-01-01

The world is undergoing exceptional biodiversity loss. Most conservation efforts target biodiversity hotspots at large scales. Such approach overlooks small-sized local hotspots, which may be rich in endemic and highly threatened species. We explore the importance of mountain rock pools (gueltas) as local biodiversity hotspots in the Sahara-Sahel. Specifically, we considered how many vertebrates (total and endemics) use gueltas, what factors predict species richness, and which gueltas are of most priority for conservation. We expected to provide management recommendations, improve local biodiversity conservation, and simultaneously contribute with a framework for future enhancement of local communities' economy. The identification of local hotspots of biodiversity is important for revaluating global conservation priorities. We quantified the number of vertebrate species from each taxonomic group and endemics present in 69 gueltas in Mauritania, then compared these with species present in a surrounding area and recorded in the country. We evaluated the predictors of species number's present in each guelta through a multiple regression model. We ranked gueltas by their priority for conservation taking into account the percentage of endemics and threats to each guelta. Within a mere aggregate extent of 43 ha, gueltas hold about 32% and 78% of the total taxa analysed and endemics of Mauritania, respectively. The number of species present in each guelta increased with the primary productivity and area of gueltas and occurrence of permanent water. Droughts and human activities threaten gueltas, while 64% of them are currently unprotected. Gueltas are crucial for local biodiversity conservation and human activities. They require urgent management plans in Mauritania's mountains. They could provide refugia under climate change being important for long-term conservation of Sahara-Sahel biodiversity. Given their disproportional importance in relation to their size, they are

Characterization of superconducting coil for fault current limitation

International Nuclear Information System (INIS)

Polasek, Alexander; Dias, Rodrigo; Niedu, Daniel Brito; Ogasawara, Tsuneharu; Oliveira Filho, Orsino Borges de; Serra, Eduardo Torres; Gomes Junior, George; Amorim, Helio Salim

2010-01-01

The increasing power demand has been raising fault currents up to dangerous levels. Superconducting fault current limiters are a promising solution for this problem. In the present work, we studied a superconducting Bi-2212 coil that is used for fault current limitation. Samples were analyzed by XRD, SEM/EDS and measurement of critical temperature (Tc). The Rietveld method was employed for phase quantification. Relatively high Bi-2212 fractions were found. However, Tc varies from a sample to another one. Variations of local Tc are attributed to variations of oxygen content in Bi- 2212 phase. (author)

Comparison of AC losses, magnetic field/current distributions and critical currents of superconducting circular pancake coils and infinitely long stacks using coated conductors

Energy Technology Data Exchange (ETDEWEB)

Yuan Weijia; Campbell, A M; Hong, Z; Ainslie, M D; Coombs, T A, E-mail: wy215@cam.ac.u [Electronic, Power and Energy Conversion Group, Electrical Engineering Division, Engineering Department, University of Cambridge, Cambridge CB3 0FA (United Kingdom)

2010-08-15

A model is presented for calculating the AC losses, magnetic field/current density distribution and critical currents of a circular superconducting pancake coil. The assumption is that the magnetic flux lines will lie parallel to the wide faces of tapes in the unpenetrated area of the coil. Instead of using an infinitely long stack to approximate the circular coil, this paper gives an exact circular coil model using elliptic integrals. A new efficient numerical method is introduced to yield more accurate and fast computation. The computation results are in good agreement with the assumptions. For a small value of the coil radius, there is an asymmetry along the coil radius direction. As the coil radius increases, this asymmetry will gradually decrease, and the AC losses and penetration depth will increase, but the critical current will decrease. We find that if the internal radius is equal to the winding thickness, the infinitely long stack approximation overestimates the loss by 10% and even if the internal radius is reduced to zero, the error is still only 60%. The infinitely long stack approximation is therefore adequate for most practical purposes. In addition, the comparison result shows that the infinitely long stack approximation saves computation time significantly.

Critical current scaling and the pivot-point in Nb3Sn strands

International Nuclear Information System (INIS)

Tsui, Y; Hampshire, D P

2012-01-01

Detailed measurements are provided of the engineering critical current density (J c ) and the index of transition (n-value) of two different types of advanced ITER Nb 3 Sn superconducting strand for fusion applications. The samples consist of one internal-tin strand (OST) and two bronze-route strands (BEAS I and BEAS II—reacted using different heat treatments). Tests on different sections of these wires show that prior to applying strain, J c is homogeneous to better than 2% along the length of each strand. J c data have been characterized as a function of magnetic field (B ≤ 14.5 T), temperature (4.2 K ≤ T ≤ 12 K) and applied axial strain ( − 1% ≤ ε A ≤ 0.8%). Strain-cycling tests demonstrate that the variable strain J c data are reversible to better than 2% when the applied axial strain is in the range of − 1% ≤ ε A ≤ 0.5%. The wires are damaged when the intrinsic strain (ε I ) is ε I ≥ 0.55% and ε I ≥ 0.23% for the OST and BEAS strands, respectively. The strain dependences of the normalized J c for each type of strand are similar to those of prototype strands of similar design measured in 2005 and 2008 to about 2% which makes them candidate strands for a round-robin interlaboratory comparison. The J c data are described by Durham, ITER and Josephson-junction parameterizations to an accuracy of about 4%. For all of these scaling laws, the percentage difference between the data and the parameterization is larger when J c is small, caused by high B, T or |ε I |. The n-values can be described by a modified power law of the form n=1+rI c s , where r and s are approximately constant and I c is the critical current. It has long been known that pivot-points (or cross-overs) in J c occur at high magnetic field and temperature. Changing the magnetic field or temperature from one side of the pivot-point to the other changes the highest J c sample to the lowest J c sample and vice versa. The pivot-point follows the B–T phase boundary

Evaluation of critical current density and residual resistance ratio limits in powder in tube Nb$_{3}$Sn conductors

CERN Document Server

Segal, Christopher; Sung, Zu Hawn; Lee, Peter J; Sailer, Bernd; Thoener, Manfred; Schlenga, Klaud; Ballarino, Amalia; Bottura, Luca; Bordini, Bernardo; Scheuerlein, Christian; Larnalestier, David C

2016-01-01

High critical current density ( Jc) Nb$_{3}$Sn A15 multifilamentary wires require a large volume fraction of small grain (SG), superconducting A15 phase, as well as Cu stabilizer with high Residual Resistance Ratio (RRR) to provide electromagnetic stabilization and protection. In powder-in-tube (PIT) wires the unreacted Nb7.5 wt%Ta outer layer of the tubular filaments acts as a diffusion barrier and protects the interfilamentary Cu stabilizer from Sn contamination. A high RRR requirement generally imposes a restricted A15 reaction heat treatment to prevent localized full reaction of the filament that could allow Sn to reach the Cu. In this study we investigate recent high quality PIT wires that achieve a Jc (12 T, 4.2 K) up to ∼2500 A mm−2 and find that the minimum diffusion barrier thickness decreases as the filament aspect ratio increases from ∼1 in the inner rings of filaments to 1.3 in the outer filament rings. We found that just 2–3 diffusion barrier breaches can degrade RRR from 300 to 150 or le...

Experimental data and calculation studies of critical heat fluxes at local disturbances of geometry of WWER fuel assemblies

International Nuclear Information System (INIS)

Kobzar, L.L.; Oleksyuk, D.A.

2001-01-01

The results of experiments executed in RRC 'Kurchatov Institute on the thermal-physical critical facility SVD are presented herein. The experiments modeled the drawing of two fuel rods to each other till touching WWER-1000 reactor in FA. The experimental model is a 7-rod bundle with the heated length of 1 m. The primary goal of experiments was to acquire the quantitative factors of the reduction in the critical heat fluxes as contrasted to the basic model (without disturbances of FA geometry) at the expense of local disturbance of a rod bundle geometry. As it follows from the experiment, the effect of decrease of the critical heat rate depends on combination of regime parameters and it makes 15% in the most unfavorable case (Authors)

A nonparametric approach to calculate critical micelle concentrations: the local polynomial regression method

Energy Technology Data Exchange (ETDEWEB)

Lopez Fontan, J.L.; Costa, J.; Ruso, J.M.; Prieto, G. [Dept. of Applied Physics, Univ. of Santiago de Compostela, Santiago de Compostela (Spain); Sarmiento, F. [Dept. of Mathematics, Faculty of Informatics, Univ. of A Coruna, A Coruna (Spain)

2004-02-01

The application of a statistical method, the local polynomial regression method, (LPRM), based on a nonparametric estimation of the regression function to determine the critical micelle concentration (cmc) is presented. The method is extremely flexible because it does not impose any parametric model on the subjacent structure of the data but rather allows the data to speak for themselves. Good concordance of cmc values with those obtained by other methods was found for systems in which the variation of a measured physical property with concentration showed an abrupt change. When this variation was slow, discrepancies between the values obtained by LPRM and others methods were found. (orig.)

Anisotropy of critical current density in the superconducting Nb/sub 3/Sn tape wires

Energy Technology Data Exchange (ETDEWEB)

Glowacki, B A [Technical Univ., Wroclaw (Poland). Inst. of Fundamental Electrotechnics and Electrotechnology

1985-04-01

In this letter the results are presented of an investigation of Isub(c parallel) and Isub(c perpendicular) in Nb/sub 3/Sn layers obtained in the process diffusion of tin atoms from liquid bronze solution Cu-80% Sn to the Nb-1.5% Zr substrate. Measurements of critical current density in Nb/sub 3/Sn layers were carried out in a perpendicular magnetic field of the induction value 4.25 T for different sample surface orientations in relation to the magnetic field strength vector defined by the value of angle. The critical current density was measured at a temperature of 4.2 K. Phase identification and investigation of the microstructure of superconducting Nb-Sn layers were performed on the Moessbauer spectrometer and scanning electron microscope, respectively. Classification measurements of grains in Nb-Sn layers were carried out with TV automatic image analyser. The texture and lattice parameter in Nb/sub 3/Sn layers were investigated by means of an X-ray diffractometer. The surface zone of Nb/sub 3/Sn layer was removed with the use of an argon ion gun. Results are presented and discussed.

Computation of quantum electron transport with local current conservation using quantum trajectories

International Nuclear Information System (INIS)

Alarcón, A; Oriols, X

2009-01-01

A recent proposal for modeling time-dependent quantum electron transport with Coulomb and exchange correlations using quantum (Bohm) trajectories (Oriols 2007 Phys. Rev. Lett. 98 066803) is extended towards the computation of the total (particle plus displacement) current in mesoscopic devices. In particular, two different methods for the practical computation of the total current are compared. The first method computes the particle and the displacement currents from the rate of Bohm particles crossing a particular surface and the time-dependent variations of the electric field there. The second method uses the Ramo–Shockley theorem to compute the total current on that surface from the knowledge of the Bohm particle dynamics in a 3D volume and the time-dependent variations of the electric field on the boundaries of that volume. From a computational point of view, it is shown that both methods achieve local current conservation, but the second is preferred because it is free from 'spurious' peaks. A numerical example, a Bohm trajectory crossing a double-barrier tunneling structure, is presented, supporting the conclusions

Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC

Science.gov (United States)

Kido, R.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Jha, A. K.; Matsumoto, K.

The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5-10 nm and 10-20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.

Current trends in local antibacterial therapy of periprosthetic infection and osteomyelitis

Directory of Open Access Journals (Sweden)

S. A. Bozhkova

2015-01-01

Full Text Available The rational use of antibiotics in the treatment of orthopedic infection still presents a significant problem. Local antibiotic delivery systems enable to achieve effective concentrations of drugs in the focus of bone infection without the development of toxicity. It is the important accompaniment to systemic antibiotics in the treatment of periprosthetic infection and osteomyelitis. The data collected through the PubMed and eLIBRARY databases (http://www.ncbi.nlm. nih.gov/pubmed, 1995-2015; http://elibrary.ru, 2005-2015 years present the information about bone substitutes used for local antibiotic therapy in scientific investigations and in clinical practice. The information is submitted in accordance with the groups of materials: cements based on polymethylmethacrylate, bone grafts, demineralized bone matrix, bioceramics, natural and synthetic polymers, combined antibiotic delivery systems. The majority of these materials have only been studied experimentally and only a limited range of them is registered for use in clinical practice. Informing orthopedic surgeons about current methods of local antibiotic use is the key to the development of a modern integrated approach to the therapy of infectious complications after orthopedic surgery.

Magnetic penetration depth δ o and critical current density in Y-BA-Cu-O crystals

International Nuclear Information System (INIS)

Zavaritsky, N.V.; Zavaritsky, V.N.

1989-01-01

Magnetic penetration depthδ o ∼1.03 10 - 5 cm and critical current density (j c = 0.5 divided-by 1 x 10 5 A/cm 2 at T/T ∼0.98) are determined from low-field do magnetization measurements on Y 1 Ba 2 Cu 3 O 7 - crystals

Angular dependence of critical current density and magnetoresistance of sputtered high-T{sub c}-films

Energy Technology Data Exchange (ETDEWEB)

Geerkens, A.; Frenck, H.J.; Ewert, S. [Technical Univ. of Cottbus (Germany)] [and others

1994-12-31

The angular dependence of the critical current density and the magnetoresistance of high-T{sub c}-films in high and low magnetic fields and for different temperatures were measured to investigate the flux pinning and the superconducting properties. A comparison of the results for the different superconductors shows their increasing dependence on the angle {Theta} between the magnetic field and the c-axis of the film due to the anisotropy of the chosen superconductor. Furthermore the influence of the current direction to the {Theta}-rotation plane is discussed.

Enhancements of the critical currents of YBaCuO single crystals by neutron (n) and proton (p) irradiation

International Nuclear Information System (INIS)

Vlcek, B.M.; Frischherz, M.C.; Vishwanathan, H.K.; Welp, U.; Crabtree, G.W.; Kirk, M.A.

1992-01-01

We present results of magnetization hysteresis and T c measurements of neutron and proton irradiated YBaCuO single crystals. The crystals used for comparison were irradiated to a fluence of 2x10 7 n/cm 2 (n,E > 0.1MeV) and 1x10 16 p/cm 2 (p,E=3.5MeV). The critical currents at 1T and 10K are enhanced by a factor of 5 for the neutron irradiated and a factor of 9 for the proton irradiated sample respectively. After irradiation the crystals were annealed at 100, 200 and 300C for 8h each in air. Following each annealing step the critical temperature and the magnetization hysteresis at 10 and 70K was measured. Upon annealing, we observe a decrease of the critical currents, which is more pronounced for the proton irradiated sample. This decrease is related to the removal of point defects or their small clusters. Thus, their contribution to pinning can be studied. The critical temperature decreases after both types of irradiation by about 0.5K and is fully recovered after annealing

Effect of the critical current density and the junction size on the leakage current of Nb/Al-AlOx/Nb superconducting tunnel junctions for radiation detection

International Nuclear Information System (INIS)

Joosse, K.; Nakagawa, Hiroshi; Akoh, Hiroshi; Takada, Susumu; Maehata, Keisuke; Ishibashi, Kenji.

1996-01-01

Nb/Al-AlO x /Nb superconducting tunnel junctions (STJ's) designed for X-ray detection have been fabricated. The behavior of the low-temperature subgap leakage current, which severely limits the energy resolution obtained in such devices, is investigated. From trends in the dependence of the leakage currents on the critical current density and the size of the STJ, as well as from the low-temperature current-voltage characteristics, and an analysis of the base electrode surface morphology, it is concluded that physical defects in the barrier region are the most probable cause of the leakage currents. Suggestions are given for optimization of the device processing. (author)

Numerical Modeling of Edge-Localized-Mode Filaments on Divertor Plates Based on Thermoelectric Currents

International Nuclear Information System (INIS)

Wingen, A.; Spatschek, K. H.; Evans, T. E.; Lasnier, C. J.

2010-01-01

Edge localized modes (ELMs) are qualitatively and quantitatively modeled in tokamaks using current bursts which have been observed in the scrape-off-layer (SOL) during an ELM crash. During the initial phase of an ELM, a heat pulse causes thermoelectric currents. They first flow in short connection length flux tubes which are initially established by error fields or other nonaxisymmetric magnetic perturbations. The currents change the magnetic field topology in such a way that larger areas of short connection length flux tubes emerge. Then currents predominantly flow in short SOL-like flux tubes and scale with the area of the flux tube assuming a constant current density. Quantitative predictions of flux tube patterns for a given current are in excellent agreement with measurements of the heat load and current flow at the DIII-D target plates during an ELM cycle.

Localized excitations in nonlinear complex systems current state of the art and future perspectives

CERN Document Server

Cuevas-Maraver, Jesús; Frantzeskakis, Dimitri; Karachalios, Nikos; Kevrekidis, Panayotis; Palmero-Acebedo, Faustino

2014-01-01

The study of nonlinear localized excitations is a long-standing challenge for research in basic and applied science, as well as engineering, due to their importance in understanding and predicting phenomena arising in nonlinear and complex systems, but also due to their potential for the development and design of novel applications. This volume is a compilation of chapters representing the current state-of-the-art on the field of localized excitations and their role in the dynamics of complex physical systems.

Transport current ac losses and current-voltage curves of multifilamentary Bi-2223/Ag tape with artificial defects

International Nuclear Information System (INIS)

Polak, M.; Jansak, L.

2000-01-01

We experimentally studied the effects of a single artificial defect and a linear array of artificial defects on I-V curves, critical currents and transport current ac losses of 55 filament untwisted Bi-2223/Ag tapes. The artificial defect was a small hole drilled into the tape. The reduction in the critical current measured on a 1 cm long section due to one hole of diameter 0.9 mm was 33% and that due to a linear array of seven similar holes was 62%. The slopes of the I-V curves, n, measured in this section were 33, 16 and 5.8 in the original sample, in the sample with one defect and the sample with seven defects, respectively. Both I c and the slope reduction were smaller if the distance between the potential taps was increased. The transport current ac losses at 50 Hz and I rms = 10 A in the sample with one defect measured in a 1 cm long section were practically the same as those in the original sample (4.1x10 -4 W m -1 ), but they increased by 83% in the sample with a linear array of seven defects. The measured increase in losses per unit length was the smaller, the larger the distance between the potential taps. A comparison between the measured and calculated losses revealed that a formal application of the Norris equations for loss calculations in samples with local defects leads to an overestimation of the ac losses. A procedure for the calculation of transport current losses in samples with local defects based on the Norris model is proposed and verified. (author)

Local governments' roles of the compensation for damage by the Tokai JCO criticality accident

International Nuclear Information System (INIS)

Tanabe, Tomoyuki

2003-01-01

The Tokai JCO criticality accident on September 30, 1999 was the first case to which The Law on Compensation for Nuclear Damage was applied. Although the Law on Compensation for Nuclear Damage formulates the outline of the institutional framework for nuclear third party liability together with operator's insurance scheme, details of actual compensation procedure are not specified. By this reason, the compensation procedure in the Tokai accident had been executed without a concrete legal specification and a precedent. In spite of this situation, the compensation procedure with the accident led to an unexpectedly successful result. We observe the several reasons why the compensation procedure was implemented successfully despite the lack of concrete legal specification and a precedent. One of the reasons is that the local governments, Tokai Village and Ibaraki Prefecture, immediately took the leadership in implementing a temporary regime of compensation procedure without wasting time for waiting national government's directives. Upon practicing this compensation procedure, the local governments implemented the following steps. (1) Initial estimation of the amount and scope of damage. (2) Providing the criteria and heads of damage subject to compensation. (3) Unitary compensation procedure at the local levels. (4) Distribution of emergency payments for the victims. (5) Facilitating compensatory negotiation between the victims and JCO as arbitrator. However, some concerns are also pointed out about the fact that the local government directed the whole procedure without sufficient adjustment with the national government for compensation policy. Among all, in the compensation led by the local governments, it was difficult to guarantee fairness of compensation because victims who are influential on the local government such as industrial associations would have unfairly strong negotiation power in the compensatory negotiation, while the operator being responsible for the

Superconducting critical-current densities of commercial multifilamentary Nb3Sn(Ti) wires made by the bronze process

International Nuclear Information System (INIS)

Suenaga, M.; Tsuchiya, K.; Higuchi, N.; Tachikawa, K.

1985-01-01

Superconducting critical-current densities Jsub(c) in fields up to 24 T and at 4.2 and 1.8 K were measured for a number of commercial Nb 3 Sn wires which were alloyed with Ti. The best values of Jsub(c) at 20 T and at 4.2 and 1.8 K were 78 and 156 A mm -2 , respectively. In order to achieve these high current densities at H>20 T, it was shown that nonuniformity of the filaments had to be minimized. It was also shown that the grain size of Nb 3 Sn is not very important in determining Jsub(c) at these high magnetic fields, and that achieving high values of critical magnetic field Hsub(c2) is more important than small grain size. (author)

Advances in superconductivity: new materials, critical currents and devices

International Nuclear Information System (INIS)

Pinto, R.; Malik, S.K.; Grover, A.K.; Ayyub, P.

1997-01-01

The discovery of superconductivity in the cuprates produced an explosive growth in research, driven by the quest for higher and higher superconducting transition temperatures. In the initial stages, the excitement was tremendous both in the physical sciences and in engineering. However, the complexity of the new materials on the one hand, and the absence of a viable theory on the other, have made further developments much more difficult. It is to be expected therefore, that the early excitement and the subsequent rapid advances have paved the way for more systematic and detailed studies of all aspects of superconductivity. The International Symposium was intended to provide a forum to review the progress in selected areas in superconductivity. The emphasis was on experimental and theoretical studies of the new superconductors, advances in the theoretical understanding, progress in studies of flux pinning and vortex dynamics which affect critical currents, and developments of novel material synthesis methods. Recent developments in the twin areas of thin films and devices were extensively discussed during the symposium. Papers relevant to INIS are indexed separately

Information technology systems for critical care triage and medical response during an influenza pandemic: a review of current systems.

Science.gov (United States)

Bandayrel, Kristofer; Lapinsky, Stephen; Christian, Michael

2013-06-01

To assess local, state, federal, and global pandemic influenza preparedness by identifying pandemic plans at the local, state, federal, and global levels, and to identify any information technology (IT) systems in these plans to support critical care triage during an influenza pandemic in the Canadian province of Ontario. The authors used advanced MEDLINE and Google search strategies and conducted a comprehensive review of key pandemic influenza Web sites. Descriptive data extraction and analysis for IT systems were conducted on all of the included pandemic plans. A total of 155 pandemic influenza plans were reviewed: 29 local, 62 state, 63 federal, and 1 global. We found 70 plans that examined IT systems (10 local, 33 state, 26 federal, 1 global), and 85 that did not (19 local, 29 state, 37 federal). Of the 70 plans, 64 described surveillance systems (10 local, 32 state, 21 federal, 1 global), 2 described patient data collection systems (1 state, 1 federal); 4 described other types of IT systems (4 federal), and none were intended for triage. Although several pandemic plans have been drafted, the majority are high-level general documents that do not describe IT systems. The plans that discuss IT systems focus strongly on surveillance, which fails to recognize the needs of a health care system responding to an influenza pandemic. The best examples of the types of IT systems to guide decision making during a pandemic were found in the Kansas and the Czech Republic pandemic plans, because these systems were designed to collect both patient and surveillance data. Although Ontario has yet to develop such an IT system, several IT systems are in place that could be leveraged to support critical care triage and medical response during an influenza pandemic.

Onset of local ordering in some copper-based alloys: critical solute concentration vis-a-vis various solutionhardening parameters

Science.gov (United States)

Butt, Muhammad Zakria; Noshi, Mozina; Bashir, Farooq

2008-12-01

The mode of planar distribution of solute atoms in Cu single crystals alloyed with 0.5 to 8.0 at.%Ge has been investigated via the temperature dependence of the critical resolved shear stress of these alloys. It is found that there exists a critical solute concentration c m ≈ 5 at.%Ge below which the distribution of solute atoms in the crystal is random, and above which some local ordering occurs. This together with such data available in the literature for Cu-Zn, Cu-Al and Cu-Mn alloys, i.e. c m ≈7 at. %Zn, 7 at.%Al and 1 at.%Mn, when examined as a function of the size-misfit factor δ = (1/ b)(d b/d c)of a given binary alloy system, shows that the value of c m strongly depends on δ; the smaller the magnitude of δ, the greater the value of c m and vice versa. Also, the value of c m is found to correlate well with the electron-to-atom ratio ( e/a)of the Cu-Zn, Cu-Al, Cu-Ge and Cu-Mn alloys with the solute concentration c = c m . However, no systematic correlation exists between the critical solute concentration c m for the onset of local ordering and the modulus-mismatch parameter η = (1/ G)(d G/d c).

Perineuronal nets increase inhibitory GABAergic currents during the critical period in rats

Directory of Open Access Journals (Sweden)

Zheng-Qin Yin

2013-04-01

Full Text Available AIM: To investigate inhibitory γ-aminobutyric acid (GABA ergic postsynaptic currents (IPSCs and postsynaptic currents (PSCs in layer IV of the rat visual cortex during the critical period and when plasticity was extended through dissolution of the perineuronal nets (PNNs.METHODS:We employed 24 normal Long-Evans rats to study GABAA-PSC characteristics of neurons within layer IV of the visual cortex during development. The animals were divided into six groups of four rats according to ages at recording:PW3 (P21-23d, PW4 (P28-30d, PW5 (P35-37d, PW6 (P42-44d, PW7 (P49-51d, and PW8 (56-58d. An additional 24 chondroitin sulfate proteoglycan (CSPG degradation rats (also Long-Evans were generated by making a pattern of injections of chondroitinase ABC (chABC into the visual cortex 1 week prior to recording at PW3, PW4, PW5, PW6, PW7, and PW8. Immunohistochemistry was used to identify the effect of chABC injection on CSPGs. PSCswere detected with whole-cell patch recordings, and GABAA receptor-mediated IPSCs were pharmacologically isolated.RESULTS:IPSC peak current showed a strong rise in the age-matched control group, peaked at PW5 and were maintained at a roughly constant value thereafter. Although there was a small increase in peak current for the chABC group with age, the peak currents continued to decrease with the delayed highest value at PW6, resulting in significantly different week-by-week comparison with normal development. IPSC decay time continued to increase until PW7 in the control group, while those in the chABC group were maintained at a stable level after an initial increase at PW4. Compared with normal rats, the decay times recorded in the chABC rats were always shorter, which differed significantly at each age. We did not observe any differences in IPSC properties between the age-matched control and penicillinase (P-ase group.However, the change in IPSCs after chABC treatment was not reflected in the total PSCs or in basic membrane

Correlations between critical current density, j{sub c}, critical temperature, T{sub c}, and structural quality of Y{sub 1}B{sub 2}Cu{sub 3}O{sub 7-x} thin superconducting films

Energy Technology Data Exchange (ETDEWEB)

Chrzanowski, J.; Xing, W.B.; Atlan, D. [Simon Fraser Univ., British Columbia (Canada)] [and others

1994-12-31

Correlations between critical current density (j{sub c}) critical temperature (T{sub c}) and the density of edge dislocations and nonuniform strain have been observed in YBCO thin films deposited by pulsed laser ablation on (001) LaAlO{sub 3} single crystals. Distinct maxima in j{sub c} as a function of the linewidths of the (00{ell}) Bragg reflections and as a function of the mosaic spread have been found in the epitaxial films. These maxima in j{sub c} indicate that the magnetic flux lines, in films of structural quality approaching that of single crystals, are insufficiently pinned which results in a decreased critical current density. T{sub c} increased monotonically with improving crystalline quality and approached a value characteristic of a pure single crystal. A strong correlation between j{sub c} and the density of edge dislocations N{sub D} was found. At the maximum of the critical current density the density of edge dislocations was estimated to be N{sub D}{approximately}1-2 x 10{sup 9}/cm{sup 2}.

Best practice in English Local Air Quality Management: principles illustrated by some examples of current practice

Energy Technology Data Exchange (ETDEWEB)

Beattie, C.I.; Ling, K.; Longhurst, J.W.S. [Univ. of the West of England, Faculty of Applied Sciences, Bristol (GB)] [and others

1999-07-01

The Local Air Quality Management (LAQM) process, a holistic approach to management, is well underway in England. The process aims to tackle air pollution problems from a variety of diverse sources, operating over different time scales and spatial areas. Although technical guidance from the Government has been published over the last two years, little guidance has been available for the management aspects of the process. Arguably, the management of air quality will be the crucial test of the LAQM process. Only by collaboration can technologies and policy actions, such as traffic management schemes, be put into effective action. The authors present an overview of the process, including a model of current LAQM procedures in the UK. Current practice is illustrated by way of results from a questionnaire survey of local authorities, health authorities and the Environment Agency and also by reference to specific examples from local authorities. (Author)

Effects of stress on critical current in V3Ga tape

International Nuclear Information System (INIS)

Okada, Touichi; Terada, R.

1979-01-01

For the generation of magnetic field less than 8T NbTi conductors have been used with considerable reliability. For the higher field (which is strongly expected for advanced SCM in near future) compound type superconductors such as Nb 3 Sn or V 3 Ga are to be used. These compound superconducting materials are, however, intrinsically brittle, so that it has been said that considerable degradation cannot be avoided, if they are subjected to certain amount of strain say, --0.1%. This is the main reason that compound superconducting materials have been hesitated to the application to the LARGE magnets. To give a clearer insight to the problem we have studied stress/strain degradation effects on commercially available superconducting V 3 Ga tape using specially designed apparatus by making ''in situ'' experiment, i.e. 1) in liquid He, 2) with external magnetic field, 3) with current in the conductor and 4) with stresses. An interesting and very important results were obtained that the critical current density increases with stress (or strain) at the first stage and degraded drastically after the sample is strained higher than about ''one percent''. (author)

Magnetization, critical current, and injection field harmonics in superconducting accelerator magnets

International Nuclear Information System (INIS)

Ghosh, A.K.; Sampson, W.B.; Wanderer, P.

1985-01-01

The very large energy ratio of machines such as the SSC dictates rather low injection field (for 6T, 20 TeV it is approximately 0.3T). Since the harmonic content at such low fields is largely determined by magnetization currents in the superconductor, the random errors depend on the uniformity of the superconducting wire. In principle the magnitude of the residual fields can be reduced indefinitely by using finer filaments, but in practice there is a lower limit of a few microns. We have compared the injection field harmonics for a number of accelerator dipoles with magnetization measurements made on samples of the conductor used to wind the coils. In addition both the magnetization and harmonics have been compared with short sample critical current measurements made at 5T. The results indicated that an accurate estimate of the variation in injection field harmonics can only be obtained from direct measurements of the magnetization of the cable. It appears feasible to use such measurements to ''shuffle'' magnets for a large accelerator by predicting the low field properties of a magnet before actually winding the coils. 10 refs., 4 figs., 2 tabs

Non-Fermi Liquid Behavior Close to a Quantum Critical Point in a Ferromagnetic State without Local Moments

Directory of Open Access Journals (Sweden)

E. Svanidze

2015-03-01

Full Text Available A quantum critical point (QCP occurs upon chemical doping of the weak itinerant ferromagnet Sc_{3.1}In. Remarkable for a system with no local moments, the QCP is accompanied by non-Fermi liquid behavior, manifested in the logarithmic divergence of the specific heat both in the ferro-and the paramagnetic states, as well as linear temperature dependence of the low-temperature resistivity. With doping, critical scaling is observed close to the QCP, as the critical exponents δ, γ, and β have weak composition dependence, with δ nearly twice and β almost half of their respective mean-field values. The unusually large paramagnetic moment μ_{PM}∼1.3μ_{B}/F.U. is nearly composition independent. Evidence for strong spin fluctuations, accompanying the QCP at x_{c}=0.035±0.005, may be ascribed to the reduced dimensionality of Sc_{3.1}In, associated with the nearly one-dimensional Sc-In chains.

Critical currents of Y sub 1 Ba sub 2 Cu sub 3 O sub 7-. delta. ceramics

Energy Technology Data Exchange (ETDEWEB)

Vasiliev, B V; Obukhov, Yu V [Joint Inst. for Nuclear Research, Low Temperature Physics Dept., Moscow (USSR)

1991-12-01

The magnetization measurements on a ceramic YBaCuO sample were carried out. The M(H,T) dependence has demonstrated some peculiarities which we suppose to be connected with H{sub j1}, H{sub j2}, H{sub C1} fields. By analizing the magnetization in the field region between H{sub j1} and H{sub j2} within the frame of the critical state model one can found the dependence of the intergranular critical current density on field and temperature. (orig.).

Systemic sclerosis and localized scleroderma--current concepts and novel targets for therapy.

Science.gov (United States)

Distler, Oliver; Cozzio, Antonio

2016-01-01

Systemic sclerosis (SSc) is a chronic autoimmune disease with a high morbidity and mortality. Skin and organ fibrosis are key manifestations of SSc, for which no generally accepted therapy is available. Thus, there is a high unmet need for novel anti-fibrotic therapeutic strategies in SSc. At the same time, important progress has been made in the identification and characterization of potential molecular targets in fibrotic diseases over the recent years. In this review, we have selected four targeted therapies, which are tested in clinical trials in SSc, for in depths discussion of their preclinical characterization. Soluble guanylate cyclase (sGC) stimulators such as riociguat might target both vascular remodeling and tissue fibrosis. Blockade of interleukin-6 might be particularly promising for early inflammatory stages of SSc. Inhibition of serotonin receptor 2b signaling links platelet activation to tissue fibrosis. Targeting simultaneously multiple key molecules with the multityrosine kinase-inhibitor nintedanib might be a promising approach in complex fibrotic diseases such as SSc, in which many partially independent pathways are activated. Herein, we also give a state of the art overview of the current classification, clinical presentation, diagnostic approach, and treatment options of localized scleroderma. Finally, we discuss whether the novel targeted therapies currently tested in SSc could be used for localized scleroderma.

Vortex lines in layered superconductors. II. Pinning and critical currents in high temperature superconductors

Science.gov (United States)

Manuel, P.

1994-02-01

In this article, a qualitative survey is given on the various phenomena which influence the critical current of high temperature superconductors. Critical current is defined as a property related to a non-zero electric field criterion, the level of which is fixed by experimental considerations, or efficiency requirements of applications. The presentation is restricted to extrinsic intragranular critical current, which depends in a complex way on the interplay between the characteristics of pinning centres and the properties of the vortex lattice. The discussion is focussed on the configuration {B} / / {c}, which contains the main elements of this problem. Differences of behaviour between Y(123) and BSCCO (Bi(2212) or Bi(2223)) are analysed in the context of their respective anisotropy factors. Possible regimes for pinning and creep are discussed in various temperature domains. From critical current results, a strong pinning regime is found to occur in BSCCO, whereas the pinning strength in Y(123) is still an open question. The thermal decrease of critical current allows a collective creep regime to appear in both materials, but at different temperature ranges. The disappearance of correlation effects near the irreversibility line results in a fall of the effective pinning energy. We show that in BSCCO, the effective pinning energy deduced from experimental results is not in agreement with pinning by randomly dispersed oxygen vacancies. Finally, we shortly describe the microstructures which could allow a more efficient pinning in future materials. On effectue une présentation qualitative des divers phénomènes qui contrôlent la valeur du courant critique dans les supraconducteurs à haute température. La notion de courant critique qui est utilisée est reliée à un critère de champ électrique non nul, fixé par des considérations expérimentales ou des exigences de rendement pour les applications. On se restreint au problème des courants critiques

SOME CONSIDERATIONS ON LOCAL FINANCIAL AUTONOMY IN THE CONTEXT OF THE CURRENT FINANCIAL CRISIS

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Vezure Oana Sabina

2012-03-01

Full Text Available Financing of local authorities is currently at the Centre of the political discourse is a daily concern. Romania faces, usually with an attempt to offset the need for control and reduction of public spending with greater financial autonomy of local authorities. At the time, it was searched and searches for a path, a means to achieve a fair distribution of financial resources between the various levels of administration, budget reductions to all of them. If strengthening democracy means to strengthen local autonomy, then it means you have created a system for financing local authorities to be efficient, fair and pointing towards the economic needs of States. In other words, decentralization and local financing and the principle of subsidiarity are mutually dependent. Rightly, the decentralisation of financial management is considered to be the "backbone" of the administrative system of decentralisation, the financial resources being those which are operational link between the needs of local communities and the rules necessary to satisfy them. Thus, the lack of financial resources of the local self-government can result in failure to meet the needs of its members, which at the same time failure of administrative decentralization. The decentralisation of financial management can also be seen as the Government of some specific functions on the line of management authority and the tax revenue to the local public authorities.

Condensate localization by mesoscale disorder in high-Tc superconductors

International Nuclear Information System (INIS)

Kumar, N.

1994-06-01

We propose and solve approximately a phenomenological model for Anderson localization of the macroscopic wavefunction for an inhomogeneous superconductor quench-disordered on the mesoscale of the order of the coherence length ξ 0 . Our treatment is based on the non-linear Schroedinger equation resulting from the Ginzburg-Landau free-energy functional having a spatially random coefficient representing spatial disorder of the pairing interaction. Linearization of the equation, valid close to the critical temperature T c , or to the upper critical field H c2 (T c ) maps it to the Anderson localization problem with T c identified with the mobility edge. For the highly anisotropic high-T c materials and thin (2D) films in the quantum Hall geometry, we predict windows of re-entrant superconductivity centered at integrally spaced temperature values. Our model treatment also provides a possible explanation for the critical current J c perpendicular becoming non-zero on cooling before J c parallel does in some high-T c superconductors. (author). 18 refs

Finite element transport methods for criticality calculations - current status and potential applications

International Nuclear Information System (INIS)

Oliveira, C.R.E. de; Goddard, A.

1991-01-01

In this paper we review the current status of the finite element method applied to the solution of the neutron transport equation and we discuss its potential role in the field of criticality safety. We show that the method's ability in handling complex, irregular geometry in two- and three-dimensions coupled with its accurate solutions potentially renders it an attractive alternative to the longer-established Monte Carlo method. Details of the most favoured form of the method - that which combines finite elements in space and spherical harmonics in angle - are presented. This form of the method, which has been extensively investigated over the last decade by research groups at the University of London, has been numerically implemented in the finite element code EVENT. The code has among its main features the capability of solving fixed source eigenvalue and time-dependent complex geometry problems in two- and three-dimensions. Other features of the code include anisotropic up- and down-scatter, direct and/or adjoint solutions and access to standard data libraries. Numerical examples, ranging from simple criticality benchmark studies to the analysis of idealised three-dimensional reactor cores, are presented to demonstrate the potential of the method. (author)

The influence of atomic disordering on the critical currents in A15 superconductors near Hsub(c1)

International Nuclear Information System (INIS)

Faehnle, M.; Kronmueller, H.

1976-01-01

By a model calculation based on the Labbe-Friedel-van-Reuth model of A15 superconductors it is shown that atomic disordering in Nb 3 Sn reduces significantly the critical current densities, jsub(c), in materials with large pinning effects. (author)

Critical current anisotropy in Ag/(Pb,Bi){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} multifilamentary tapes: influence of self-magnetic field

Energy Technology Data Exchange (ETDEWEB)

Majoros, M [IRC in Superconductivity, University of Cambridge, Cambridge (United Kingdom); Institute of Electrical Engineering, Slovak Academy of Sciences, Bratislava (Slovakia); Glowacki, B A [IRC in Superconductivity, University of Cambridge, Cambridge (United Kingdom); Department of Materials Science and Metallurgy, University of Cambridge, Cambridge (United Kingdom); Campbell, A M [IRC in Superconductivity, University of Cambridge, Cambridge (United Kingdom)

2001-06-01

Two factors affect critical current anisotropy in multifilamentary Ag/(Pb,Bi){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} tapes - the intrinsic material anisotropy and the geometry. Experimental results on the magnetic field dependence and anisotropy of the critical current in a multifilamentary Ag/(Pb,Bi){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} tape after correction for self-magnetic field effects were found to fit the anisotropic Kim relation. Based on this relation a finite-element-method numerical code for solving the nonlinear Poisson equation for vector magnetic potential was adopted. It allowed the experimental data to be reproduced by back calculation and made possible the study of the interplay of self and external magnetic fields in different cases with well defined physical parameters of the material. The model was used to analyse the distribution of the critical current in individual filaments as well as to evaluate the influence of their geometrical arrangements on the critical current of the tape. The self-field critical current of an individual filament 'extracted' from the tape was compared with the critical current of the overall tape. The effect of the self-magnetic field on critical current distribution obtained by the cutting method was determined. The critical currents of the tapes with different cross sections were calculated and compared with experiments and the influence of the self-field was analysed. The anisotropic properties of a low anisotropy architecture of a multifilamentary Ag/(Pb,Bi){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} conductor were studied. The dependence of critical currents (normalized to self-field critical currents) on external magnetic field corrected for the self-field was found to follow nearly the same curves as those for tapes with different critical current densities (in the range 20-70 kA cm{sup -2} in a self-field), which makes the numerical model applicable to different tapes. (author)

Correlation between in-field critical currents in Zr-added (Gd, Y)Ba2Cu3Ox superconducting tapes at 30 and 77 K

Energy Technology Data Exchange (ETDEWEB)

Selvamanickam, V; Xu, A; Liu, Y; Khatri, ND; Lei, C; Chen, Y; Galstyan, E; Majkic, G

2014-03-11

Critical current (I-c) values of 1384 Lambda/12 mm, corresponding to a critical current density of 12.47 MA cm(-2) and a pinning force of 374 GN m(-3), have been achieved at 30 K, 3 T in the orientation of field parallel to the c axis (B parallel to c) in (Gd, Y)BaCuO tapes with 15 mol% Zr addition made by metal organic chemical vapor deposition (MOCVD). These tapes show pinning force levels as high as 453 GN m(-3) at 30 K. An analysis of the properties of 24-28 (Gd, Y)BaCuO tapes with 15 mol% Zr addition showed a lack of correlation between their critical currents at 30 K, 3 T (B parallel to c) and I-c values both at 77 K, zero field and at 77 K, 1 T (B parallel to c). However, a strong correlation was found between the critical currents at 30 K, 3 T and at 77 K, 3 T (B parallel to c). It has also been discovered that the minimum critical current (I-c, (min)) value at 77 K, 3 T has no influence on the I-c,I- (min) value at 30 K, 3 T, and it in turn depends on the ratio of the I-c values in the orientations of field parallel and perpendicular to the c axis at 77 K, 3 T.

Influence of copper volume fraction on tensile strain/stress tolerances of critical current in a copper-plated DyBCO-coated conductor

International Nuclear Information System (INIS)

Ochiai, Shojiro; Okuda, Hiroshi; Arai, Takahiro; Sugano, Michinaka; Osamura, Kozo; Prusseit, Werner

2013-01-01

The influence of the volume fraction (V f ) of copper, plated at room temperature over a DyBa 2 Cu 3 O 7-δ -coated conductor, on the tensile strain tolerance and stress tolerance of critical current at 77 K was studied over a wide range of copper V f values. The copper plating exerts a tensile stress during cooling because copper has a higher coefficient of thermal expansion than the substrate conductor. Before application of tensile strain, the copper plated at room temperature yielded at 77 K when the copper V f was lower than a critical value, and was in an elastic state at 77 K when the copper V f was higher than the critical value. The strain tolerance of critical current increased with increasing copper V f due to an increase in thermally induced compressive strain in the substrate tape. The stress tolerance of critical current decreased with increasing copper V f because copper is softer than the substrate tape. These results, together with the trade-off between strain tolerance and stress tolerance (i.e., stress tolerance decreases with increasing strain tolerance), were analyzed by modeling. The results show that the restriction imposed by the trade-off, which limits the ability to simultaneously obtain a high strain tolerance and a high stress tolerance, can be relaxed by strengthening the copper. (author)

Physics of the current injection process during localized helicity injection

Science.gov (United States)

Hinson, Edward Thomas

An impedance model has been developed for the arc-plasma cathode electron current source used in localized helicity injection tokamak startup. According to this model, a potential double layer (DL) is established between the high-density arc plasma (narc ˜ 1021 m-3) in the electron source, and the less-dense external tokamak edge plasma (nedge ˜ 10 18 m-3) into which current is injected. The DL launches an electron beam at the applied voltage with cross-sectional area close to that of the source aperture: Ainj ≈ 2 cm 2. The injected current, Iinj, increases with applied voltage, Vinj, according to the standard DL scaling, Iinj ˜ V(3/2/ inj), until the more restrictive of two limits to beam density nb arises, producing Iinj ˜ V(1/2/inj), a scaling with beam drift velocity. For low external tokamak edge density nedge, space-charge neutralization of the intense electron beam restricts the injected beam density to nb ˜ nedge. At high Jinj and sufficient edge density, the injected current is limited by expansion of the DL sheath, which leads to nb ˜ narc. Measurements of narc, Iinj , nedge, Vinj, support these predicted scalings, and suggest narc as a viable control actuator for the source impedance. Magnetic probe signals ≈ 300 degrees toroidally from the injection location are consistent with expectations for a gyrating, coherent electron beam with a compact areal cross-section. Technological development of the source has allowed an extension of the favorable Iinj ˜ V(1/2/inj) to higher power without electrical breakdown.

Local anesthetics for brain tumor resection: current perspectives

Directory of Open Access Journals (Sweden)

Potters JW

2018-02-01

Full Text Available Jan-Willem Potters, Markus Klimek Department of Anesthesiology, Erasmus MC, Rotterdam, The Netherlands Abstract: This review summarizes the added value of local anesthetics in patients undergoing craniotomy for brain tumor resection, which is a procedure that is carried out frequently in neurosurgical practice. The procedure can be carried out under general anesthesia, sedation with local anesthesia or under local anesthesia only. Literature shows a large variation in the postoperative pain intensity ranging from no postoperative analgesia requirement in two-thirds of the patients up to a rate of 96% of the patients suffering from severe postoperative pain. The only identified causative factor predicting higher postoperative pain scores is infratentorial surgery. Postoperative analgesia can be achieved with multimodal pain management where local anesthesia is associated with lower postoperative pain intensity, reduction in opioid requirement and prevention of development of chronic pain. In awake craniotomy patients, sufficient local anesthesia is a cornerstone of the procedure. An awake craniotomy and brain tumor resection can be carried out completely under local anesthesia only. However, the use of sedative drugs is common to improve patient comfort during craniotomy and closure. Local anesthesia for craniotomy can be performed by directly blocking the six different nerves that provide the sensory innervation of the scalp, or by local infiltration of the surgical site and the placement of the pins of the Mayfield clamp. Direct nerve block has potential complications and pitfalls and is technically more challenging, but mostly requires lower total doses of the local anesthetics than the doses required in surgical-site infiltration. Due to a lack of comparative studies, there is no evidence showing superiority of one technique versus the other. Besides the use of other local anesthetics for analgesia, intravenous lidocaine administration has

Evaluation as a critical factor of success in local public health accreditation programs.

Science.gov (United States)

Tremain, Beverly; Davis, Mary; Joly, Brenda; Edgar, Mark; Kushion, Mary L; Schmidt, Rita

2007-01-01

This article presents the variety of approaches used to conduct evaluations of performance improvement or accreditation systems, while illustrating the complexity of conducting evaluations to inform local public health practice. We, in addition, hope to inform the Exploring Accreditation Program about relevant experiences involving accreditation and performance assessment processes, specifically evaluation, as it debates and discusses a national voluntary model. A background of each state is given. To further explore these issues, interviews were conducted with each state's evaluator to gain more in-depth information on the many different evaluation strategies and approaches used. On the basis of the interviews, the authors provide several overall themes, which suggest that evaluation is a critical tool and success factor for performance assessment or accreditation programs.

Heat treatment effect on the strain dependence of the critical current for an internal-tin processed Nb3Sn strand

International Nuclear Information System (INIS)

Oh, Sangjun; Park, Soo-Hyeon; Lee, Chulhee; Choi, Heekyung; Kim, Keeman

2010-01-01

A comparative study on the effects of heat treatment, especially, the duration of the A15 reaction temperature plateau on the strain dependence of the critical current for an internal-tin processed Nb 3 Sn strand has been carried out. The strain dependence of the critical current is measured by a variable temperature Walter spiral probe that we have developed. It was shown that prolonged heat treatment can be a very effective way to improve the strain dependency. For a quantitative analysis, the measured data were analyzed with various proposed scaling laws: the scaling law based on strong-coupling theory, the modified deviatoric strain scaling law, and the interpolative scaling law. We found that there is a slight increase in the critical temperature and a substantial improvement in the maximum pinning force. The origin of improved strain dependency is further discussed.

Enhancement of the critical current density in FeO-coated MgB2 thin films at high magnetic fields

Directory of Open Access Journals (Sweden)

Andrei E. Surdu

2011-12-01

Full Text Available The effect of depositing FeO nanoparticles with a diameter of 10 nm onto the surface of MgB2 thin films on the critical current density was studied in comparison with the case of uncoated MgB2 thin films. We calculated the superconducting critical current densities (Jc from the magnetization hysteresis (M–H curves for both sets of samples and found that the Jc value of FeO-coated films is higher at all fields and temperatures than the Jc value for uncoated films, and that it decreases to ~105 A/cm2 at B = 1 T and T = 20 K and remains approximately constant at higher fields up to 7 T.

Spatial variations in composition in high-critical-current-density Bi-2223 tapes

International Nuclear Information System (INIS)

Holesinger, T. G.; Bingert, J. F.; Teplitsky, M.; Li, Q.; Parrella, R.; Rupich, M. P.; Riley, G. N. Jr.

2000-01-01

A detailed compositional analysis of high-critical-current-density (J c ) (55 and 65 kA/cm2 at 77 K) (Bi, Pb) 2 Sr 2 Ca 2 Cu 3 O y (Bi-2223) tapes was undertaken by energy dispersive spectroscopy in the transmission electron microscope. Structural features were coupled with characteristic compositions of the Bi-2223 phase. The average of all compositional measurements of the Bi-2223 phase was determined to be Bi 1.88 Pb 0.23 Sr 1.96 Ca 1.95 Cu 2.98 O y . However, spatial variations in the Bi-2223 composition and differing phase equilibria were found throughout the filament structure. In particular, a considerable range of Bi-2223 compositions can be found within a single tape, and the lead content of the Bi-2223 phase is significantly depressed in the vicinity of lead-rich phases. The depletion of lead in the Bi-2223 phase around the 3221 phases may be a current-limiting microstructure in these tapes. (c) 2000 Materials Research Society

Pulsed critical current measurements of NbTi in perpendicular and parallel pulsed magnetic fields using the new Cryo-BI-Pulse System

International Nuclear Information System (INIS)

Stehr, V; Tan, K S; Hopkins, S C; Glowacki, B A; Keyser, A De; Bockstal, L Van; Deschagt, J

2006-01-01

Rapid transport current versus high magnetic field characterisation of high-irreversibility type II superconductors is important to maximise their critical parameters. HTS conductors are already used to produce insert coils that increase the fields of conventional magnets made from NbTi (Nb, Ta) 3 Sn and Nb 3 Al wires. There is fundamental interest in the study of HTS tapes and wires in magnetic fields higher than 21T, the current limit of superconducting magnets producing a DC field. Such fields can be obtained by using pulse techniques. High critical currents cannot be routinely measured with a continuous current applied at liquid helium, hydrogen or neon temperatures because of thermal and mechanical effects. A newly developed pulsed magnetic field and pulsed current system which allows rapid J c (B, T) measurements of the whole range of superconducting materials was tested with a multifilamentary NbTi wire in perpendicular and parallel orientations

Critical current simulation in granular superconductors above the percolation threshold

Science.gov (United States)

Riedinger, Roland

1992-02-01

In the phase-coherent regime without applied external magnetic field, the critical superconducting current is limited by intragranular junctions which behave like Josephson junctions. We study the percolation aspects specific to lattices of such junctions and/or the mixing of superconductor with normal grains by averaging over configurations. We illustrate on 2 and 3 dimensional examples. The power laws valid near the percolation threshold are valid well above it, in two and three dimensions. We discuss the other models limiting the superconducting current, the vortex creep and superconducting order parameter fluctuations. Dans la limite de champ magnétique nul et de cohérence de phase du paramètre d'ordre supraconducteur, le courant supraconducteur maximal dans un réseau est limité par les jonctions intergranulaires qui se comportent comme des jonctions Josephson. Nous analysons les problèmes de percolation spécifiques aux réseaux de jonctions et du mélange de grains normaux et supraconducteurs. Nous donnons des exemples bidimensionnels et tridimensionnels ; après moyenne sur les configurations et analyse en taille finie, nous montrons que les lois de puissance valables au voisinage du seuil de percolation s'étendent sur un grand domaine au-delà du seuil de percolation, à deux et trois dimensions. Nous discutons les autres modèles limitant le courant supraconducteur, ancrage de vortex et fluctuations du paramètre d'ordre.

Effect of external magnetic field on critical current for the onset of virtual cathode oscillations in relativistic electron beams

International Nuclear Information System (INIS)

Hramov, Alexander; Koronovskii, Alexey; Morozov, Mikhail; Mushtakov, Alexander

2008-01-01

In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [D.J. Sullivan, J.E. Walsh, E. Coutsias, in: V.L. Granatstein, I. Alexeff (Eds.), Virtual Cathode Oscillator (Vircator) Theory, in: High Power Microwave Sources, vol. 13, Artech House Microwave Library, 1987, Chapter 13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields

Local governments' roles of the compensation for damage by the Tokai JCO criticality accident

Energy Technology Data Exchange (ETDEWEB)

Tanabe, Tomoyuki [Central Research Inst. of Electric Power Industry, Tokyo (Japan). Socio-Economic Research Center

2003-03-01

The Tokai JCO criticality accident on September 30, 1999 was the first case to which The Law on Compensation for Nuclear Damage was applied. Although the Law on Compensation for Nuclear Damage formulates the outline of the institutional framework for nuclear third party liability together with operator's insurance scheme, details of actual compensation procedure are not specified. By this reason, the compensation procedure in the Tokai accident had been executed without a concrete legal specification and a precedent. In spite of this situation, the compensation procedure with the accident led to an unexpectedly successful result. We observe the several reasons why the compensation procedure was implemented successfully despite the lack of concrete legal specification and a precedent. One of the reasons is that the local governments, Tokai Village and Ibaraki Prefecture, immediately took the leadership in implementing a temporary regime of compensation procedure without wasting time for waiting national government's directives. Upon practicing this compensation procedure, the local governments implemented the following steps. (1) Initial estimation of the amount and scope of damage. (2) Providing the criteria and heads of damage subject to compensation. (3) Unitary compensation procedure at the local levels. (4) Distribution of emergency payments for the victims. (5) Facilitating compensatory negotiation between the victims and JCO as arbitrator. However, some concerns are also pointed out about the fact that the local government directed the whole procedure without sufficient adjustment with the national government for compensation policy. Among all, in the compensation led by the local governments, it was difficult to guarantee fairness of compensation because victims who are influential on the local government such as industrial associations would have unfairly strong negotiation power in the compensatory negotiation, while the operator being

Strange metal from local quantum chaos

Science.gov (United States)

Ben-Zion, Daniel; McGreevy, John

2018-04-01

How to make a model of a non-Fermi-liquid metal with efficient current dissipation is a long-standing problem. Results from holographic duality suggest a framework where local critical fermionic degrees of freedom provide both a source of decoherence for the Landau quasiparticle, and a sink for its momentum. This leads us to study a Kondo lattice type model with SYK models in place of the spin impurities. We find evidence for a stable phase at intermediate couplings.

Electron mean free path dependence of the critical currents and the pair-breaking limit in superconducting films

International Nuclear Information System (INIS)

Fedorov, N.; Rinderer, L.

1977-01-01

We have studied the current-induced breakdown of superconductivity in wide (100--980 μm) and thin (0.25--0.98 μm) films of tin. It is shown that the current at which the resistance of the sample begins to rise rapidly in the process of the destruction of superconductivity by a current can be fairly well associated with the theoretical value of the pair-breaking current in the Ginzburg-Landau phenomenological approach (I/sub c//sup G L/). This effect is observed over a rather wide temperature region (up to ΔTapprox.0.7 K), depending on the electron mean free path in the films. The values of the critical currents outside the above-mentioned region correlate qualitatively with those determined by inhomogeneities of the films as proposed by Larkin and Ovchinnikov

Improved critical current densities of bulk MgB.sub.2./sub. using carbon-coated amorphous boron

Czech Academy of Sciences Publication Activity Database

Muralidhar, M.; Higuchi, M.; Jirsa, Miloš; Diko, P.; Kokal, I.; Murakami, M.

2017-01-01

Roč. 27, č. 4 (2017), s. 1-4, č. článku 6201104. ISSN 1051-8223 Institutional support: RVO:68378271 Keywords : carbon-encapsulated boron * critical current density * flux pinning * micro-structure Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.092, year: 2015

Localization of Narrowband Single Photon Emitters in Nanodiamonds.

Science.gov (United States)

Bray, Kerem; Sandstrom, Russell; Elbadawi, Christopher; Fischer, Martin; Schreck, Matthias; Shimoni, Olga; Lobo, Charlene; Toth, Milos; Aharonovich, Igor

2016-03-23

Diamond nanocrystals that host room temperature narrowband single photon emitters are highly sought after for applications in nanophotonics and bioimaging. However, current understanding of the origin of these emitters is extremely limited. In this work, we demonstrate that the narrowband emitters are point defects localized at extended morphological defects in individual nanodiamonds. In particular, we show that nanocrystals with defects such as twin boundaries and secondary nucleation sites exhibit narrowband emission that is absent from pristine individual nanocrystals grown under the same conditions. Critically, we prove that the narrowband emission lines vanish when extended defects are removed deterministically using highly localized electron beam induced etching. Our results enhance the current understanding of single photon emitters in diamond and are directly relevant to fabrication of novel quantum optics devices and sensors.

Magnetohydrodynamic equilibria and local stability of axisymmetric tokamak plasmas

International Nuclear Information System (INIS)

Peng, Y.K.M.; Dory, R.A.; Nelson, D.B.; Sayer, R.O.

1976-07-01

Axisymmetric magnetohydrodynamic equilibria are evaluated in terms of the Mercier Stability Criterion. The parameters of interest include poloidal beta (β/sub p/), current and pressure profile widths, D-shaped and doublet plasmas with elongation (sigma) and triangularity (delta), and the aspect ratio (A). For marginal local stability, the critical values of β, plasma current, and the safety factor q with fixed toroidal field at the geometric center of the plasma are obtained. It is shown that for a wide range of profiles in a D-shaped plasma with A = 3, the highest critical β occurs at β/sub p/ = 2.4, sigma = 1.65, and delta = 0.5. If the toroidal field at the coil surface is fixed, the highest critical pressure occurs near A approximately 3 to 4, given reasonable distance between the coils and the plasma edge. Calculations for a Doublet II-A plasma with sigma = 3 show that with similar pressure profile the highest critical β occurs at β/sub p/ = 1 and is 84 percent of the highest critical β for the D-shaped plasmas. Critical values of ohmic heating power density are also found to be comparable for the two plasma shapes. A D-shaped plasma with the above parameters is suggested for use in future high-β tokamak devices

Critical current density, irreversibility line, and flux creep activation energy in silver-sheathed Bi2Sr2Ca2Cu3Ox superconducting tapes

International Nuclear Information System (INIS)

Shi, D.; Wang, Z.; Sengupta, S.; Smith, M.; Goodrich, L.F.; Dou, S.X.; Liu, H.K.; Guo, Y.C.

1992-08-01

Transport data, magnetic hysteresis and flux creep activation energy experimental results are presented for silver-sheathed high-T c Bi 2 Sr 2 Ca 2 Cu 3 O x superconducting tapes. The 110 K superconducting phase was formed by lead doping in a Bi-Sr-Ca-Cu-0 system. The transport critical current density was measured at 4.0 K to be 0.7 x 10 5 A/cm 2 (the corresponding critical current is 74 A) at zero field and 1.6 x 10 4 A/cm 2 at 12 T for H parallel ab. Excellent grain alignment in the a-b plane was achieved by a short-melting method, which considerably improved the critical current density and irreversibility line. Flux creep activation energy as a function of current is obtained based on the magnetic relaxation measurements

Critical current measurements of high-temperature superconducting short samples at a wide range of temperatures and magnetic fields

Science.gov (United States)

Ma, Hongjun; Liu, Huajun; Liu, Fang; Zhang, Huahui; Ci, Lu; Shi, Yi; Lei, Lei

2018-01-01

High-Temperature Superconductors (HTS) are potential materials for high-field magnets, low-loss transmission cables, and Superconducting Magnetic Energy Storage (SMES) due to their high upper critical magnetic field (Hc2) and critical temperature (Tc). The critical current (Ic) of HTS, which is one of the most important parameters for superconductor application, depends strongly on the magnetic fields and temperatures. A new Ic measurement system that can carry out accurate Ic measurement for HTS short samples with various temperatures (4.2-80 K), magnetic fields (0-14 T), and angles of the magnetic field (0°-90°) has been developed. The Ic measurement system mainly consists of a measurement holder, temperature-control system, background magnet, test cryostat, data acquisition system, and DC power supply. The accuracy of temperature control is better than ±0.1 K over the 20-80 K range and ±0.05 K when measured below 20 K. The maximum current is over 1000 A with a measurement uncertainty of 1%. The system had been successfully used for YBa2Cu3O7-x(YBCO) tapes Ic determination with different temperatures and magnetic fields.

Critical current measurements of high-temperature superconducting short samples at a wide range of temperatures and magnetic fields.

Science.gov (United States)

Ma, Hongjun; Liu, Huajun; Liu, Fang; Zhang, Huahui; Ci, Lu; Shi, Yi; Lei, Lei

2018-01-01

High-Temperature Superconductors (HTS) are potential materials for high-field magnets, low-loss transmission cables, and Superconducting Magnetic Energy Storage (SMES) due to their high upper critical magnetic field (H c2 ) and critical temperature (T c ). The critical current (I c ) of HTS, which is one of the most important parameters for superconductor application, depends strongly on the magnetic fields and temperatures. A new I c measurement system that can carry out accurate I c measurement for HTS short samples with various temperatures (4.2-80 K), magnetic fields (0-14 T), and angles of the magnetic field (0°-90°) has been developed. The I c measurement system mainly consists of a measurement holder, temperature-control system, background magnet, test cryostat, data acquisition system, and DC power supply. The accuracy of temperature control is better than ±0.1 K over the 20-80 K range and ±0.05 K when measured below 20 K. The maximum current is over 1000 A with a measurement uncertainty of 1%. The system had been successfully used for YBa 2 Cu 3 O 7-x (YBCO) tapes I c determination with different temperatures and magnetic fields.

Current practices in the identification of critical habitat for threatened species.

Science.gov (United States)

Camaclang, Abbey E; Maron, Martine; Martin, Tara G; Possingham, Hugh P

2015-04-01

The term critical habitat is used to describe the subset of habitat that is essential to the survival and recovery of species. Some countries legally require that critical habitat of listed threatened and endangered species be identified and protected. However, there is little evidence to suggest that the identification of critical habitat has had much impact on species recovery. We hypothesized that this may be due at least partly to a mismatch between the intent of critical habitat identification, which is to protect sufficient habitat for species persistence and recovery, and its practice. We used content analysis to systematically review critical habitat documents from the United States, Canada, and Australia. In particular, we identified the major trends in type of information used to identify critical habitat and in occupancy of habitat identified as critical. Information about population viability was used to identify critical habitat for only 1% of the species reviewed, and for most species, designated critical habitat did not include unoccupied habitat. Without reference to population viability, it is difficult to determine how much of a species' occupied and unoccupied habitat will be required for persistence. We therefore conclude that the identification of critical habitat remains inconsistent with the goal of protecting sufficient habitat to support persistence and recovery of the species. Ensuring that critical habitat identification aligns more closely with its intent will improve the accuracy of the designations and may therefore help improve the benefits to species recovery when combined with adequate implementation and enforcement of legal protections. © 2014 Society for Conservation Biology.

Critical current density measurement of thin films by AC susceptibility based on the penetration parameter h

DEFF Research Database (Denmark)

Li, Xiao-Fen; Grivel, Jean-Claude; Abrahamsen, Asger B.

2012-01-01

We have numerically proved that the dependence of AC susceptibility χ of a E(J) power law superconducting thin disc on many parameters can be reduced to one penetration parameter h, with E the electric field and J the current density. Based on this result, we propose a way of measuring the critical...... current density Jc of superconducting thin films by AC susceptibility. Compared with the normally used method based on the peak of the imaginary part, our method uses a much larger range of the AC susceptibility curve, thus allowing determination of the temperature (T) dependence of Jc from a normally...

Critical Education, Critical Pedagogies, Marxist Education in the United States

Science.gov (United States)

Foley, Jean Ann; Morris, Doug; Gounari, Panayota; Agostinone-Wilson, Faith

2015-01-01

As critical pedagogy becomes more mainstream on the educational landscape in the United States, it is important to revisit the original tenets of critical pedagogy and explore their current manifestations. Since the beginning of "criticalism" from the theoretical/foundational work of the Frankfurt School of Critical Social Theory,…

Transcranial direct current stimulation (tDCS) to improve naming ability in post-stroke aphasia: A critical review.

Science.gov (United States)

ALHarbi, Mohammed F; Armijo-Olivo, Susan; Kim, Esther S

2017-08-14

Transcranial Direct Current Stimulation (tDCS) is a non-invasive neuromodulation tool that can be used to influence cortical brain activity to induce measurable behavioral changes. Although there is growing evidence that tDCS combined with behavioural language therapy could boost language recovery in patients with post-stroke aphasia, there is great variability in patient characteristics, treatment protocols, and outcome measures in these studies that poses challenges for analyzing the evidence. The purpose of this study is to critically analyze the methodological rigor of the evidence regarding the use of tDCS for post-stroke anomia. This critical review was conducted by searching four databases (MEDLINE, EMBase, PsycINFO, and CINAHL). Nineteen studies fully met the inclusion criteria. Three critical appraisal tools and Robey and Schultz's (1998) five- phase model for conducting clinical outcome research were adopted to evaluate and analyze the current level of evidence. Methodological issues of the studies were also identified. The current level of evidence for using tDCS for anomia is at the pre-efficacy level with emerging evidence at the efficacy level. Lack of proper evaluation of carry-over effects in cross-over studies, lack of or unclear randomization, allocation concealment, and incomplete data handling were the main methodological issues that could threaten the validity of the tDCS for anomia studies. Several methodological issues have been identified in pre-efficacy studies that pose challenges in determining whether tDCS is a beneficial adjunct to behavioral aphasia therapy. Future studies need to improve the quality of the methods used to investigate the effect of tDCS for anomia. Copyright © 2017 Elsevier B.V. All rights reserved.

Current reversals and metastable states in the infinite Bose-Hubbard chain with local particle loss

Science.gov (United States)

Kiefer-Emmanouilidis, M.; Sirker, J.

2017-12-01

We present an algorithm which combines the quantum trajectory approach to open quantum systems with a density-matrix renormalization-group scheme for infinite one-dimensional lattice systems. We apply this method to investigate the long-time dynamics in the Bose-Hubbard model with local particle loss starting from a Mott-insulating initial state with one boson per site. While the short-time dynamics can be described even quantitatively by an equation of motion (EOM) approach at the mean-field level, many-body interactions lead to unexpected effects at intermediate and long times: local particle currents far away from the dissipative site start to reverse direction ultimately leading to a metastable state with a total particle current pointing away from the lossy site. An alternative EOM approach based on an effective fermion model shows that the reversal of currents can be understood qualitatively by the creation of holon-doublon pairs at the edge of the region of reduced particle density. The doublons are then able to escape while the holes move towards the dissipative site, a process reminiscent—in a loose sense—of Hawking radiation.

Critical Failure Factors in Selling Shoplots towards Sustainability of New Township Development

Directory of Open Access Journals (Sweden)

Tawil N.M.

2014-01-01

Full Text Available The focus of this research is to identify the critical factors of shop houses sale failure in Nilai New Township. The critical factors of sale failure of commercial property types, shop houses in new township need to be discover as reported by Valuation and Property Services Department (JPPH showed 5,931 units of shop houses in Malaysia is currently completed but remained unsold where Johor was recorded as the highest with unsold units followed by Negeri Sembilan. Thus Nilai New towship is chosen as research sample for unsold shop houses units due to its strategic location which is near to KLIA, International Sepang Circuit, educational instituitions and surrounded by housing scheme but yet still has numbers of unsold units. Data was gathered from survey question between developers, local authority, purchasers/tenant and local residents.. Generally, the factors of sale failure are economy, demography, politic, location and access, public and basic facilities, financial loan, physical of product, current stock of shop houses upon completion, future potential of subsale and rental, developer’s background, promotion and marketing, speculation and time.

High-transport current density up to 30 T in bulk YBa2Cu3O7 and the critical angle effect

International Nuclear Information System (INIS)

Ekin, J.W.; Salama, K.; Selvamanickam, V.

1991-01-01

Measurements of the dc transport critical current of oriented-grained YBa 2 Cu 3 O 7 have been made using high quality Ag contacts and a high-current sample mount. The critical- current density J c at 77 K for mutually perpendicular current and magnetic field B in the a,b plane is 8 kA/cm 2 at 8 T, decreasing gradually to 3.7 kA/cm 2 at 20 T, and remaining over 1 kA/cm 2 out to 30 T. High magnetic field measurements of J c as a function of the angle θ of B with respect to the c axis are also reported. In contrast to earlier results at lower fields ( c vs θ curve with a head-and-shoulders shape, consisting of a sharp peak (''head'') 2 planes, and a wide (30 degree at 9 T, for example) shoulder region on either side of B perpendicular c, where the transport J c remains high and constant. Beyond the shoulder region, however, the transport J c decreases sharply, giving rise to the concept of a critical field angle for application design, defined by the minima in d 2 J c /dθ 2 at the edge of the shoulders

Phthalocyanine doping to improve critical current densities in MgB2 tapes

International Nuclear Information System (INIS)

Zhang Xianping; Ma Yanwei; Wang Dongliang; Gao Zhaoshun; Wang Lei; Qi Yanpeng; Awaji, Satoshi; Watanabe, Kazuo; Mossang, Eric

2009-01-01

Phthalocyanine-doped MgB 2 tapes were prepared by the in situ powder-in-tube method. The relationships between the critical current properties, crystallinity and microstructure were studied as a function of the phthalocyanine doping level. It is found that both H irr and H c2 were improved when MgB 2 samples were doped with phthalocyanine, which are mainly attributed to the effective carbon substitution and enhanced flux pinning strength caused by very fine grain sizes. Furthermore, compared to pure samples, the MgO content remained almost unchanged in all doped tapes, which is very beneficial to having better grain connectivity in MgB 2 . Significantly improved J c was obtained in the phthalocyanine-doped MgB 2 tapes, especially under high magnetic fields.

Localized Edge Vibrations and Edge Reconstruction by Joule Heating in Graphene Nanostructures

DEFF Research Database (Denmark)

Engelund, Mads; Fürst, Joachim Alexander; Jauho, Antti-Pekka

2010-01-01

Control of the edge topology of graphene nanostructures is critical to graphene-based electronics. A means of producing atomically smooth zigzag edges using electronic current has recently been demonstrated in experiments [Jia et al., Science 323, 1701 (2009)]. We develop a microscopic theory...... for current-induced edge reconstruction using density functional theory. Our calculations provide evidence for localized vibrations at edge interfaces involving unpassivated armchair edges. We demonstrate that these vibrations couple to the current, estimate their excitation by Joule heating, and argue...

c-Axis correlated extended defects and critical current in YBa2Cu3Ox films grown on Au and Ag-nano dot decorated substrates

International Nuclear Information System (INIS)

Mikheenko, P.; Sarkar, A.; Dang, V.-S.; Tanner, J.L.; Abell, J.S.; Crisan, A.

2009-01-01

We report measurements of critical current in YBa 2 Cu 3 O x films deposited on SrTiO 3 substrates decorated with silver and gold nanodots. An increase in critical current in these films, in comparison with the films deposited on non-decorated substrates, has been achieved. We argue that this increase comes from the c-axis correlated extended defects formed in the films and originated from the nanodots. Additionally to creating extended defects, the nanodots pin them and prevent their exit from the sample during the film growth, thus keeping a high density of defects and providing a lower rate of decrease of the critical current with the thickness of the films. The best pinning is achieved in the samples with silver nanodots by optimising their deposition temperature. The nanodots grown at a temperature of a few hundred deg. C have a small diameter of a few nanometres and a high surface density of 10 11 -10 12 particles/cm 2 . We give evidence of c-axis correlated extended defects in YBa 2 Cu 3 O x films by planar and cross-sectional atomic force microscopy, transmission electron microscopy and angle-dependent transport measurements of critical current.

Strain induced irreversible critical current degradation in highly dense Bi-2212 round wire

CERN Document Server

Bjoerstad, R; Rikel, M.O.; Ballarino, A; Bottura, L; Jiang, J; Matras, M; Sugano, M; Hudspeth, J; Di Michiel, M

2015-01-01

The strain induced critical current degradation of overpressure processed straight Bi 2212/Ag wires has been studied at 77 K in self-field. For the first time superconducting properties, lattice distortions, composite wire stress and strain have been measured simultaneously in a high energy synchrotron beamline. A permanent Ic degradation of 5% occurs when the wire strain exceeds 0.60%. At a wire strain of about 0.65% a drastic n value and Ic reduction occur, and the composite stress and the Bi-2212 lattice parameter reach a plateau, indicating Bi-2212 filament fracturing. The XRD measurements show that Bi-2212 exhibits linear elastic behaviour up to the irreversible strain limit.

Resistive current limiter with high-temperature superconductors. Final report

International Nuclear Information System (INIS)

Schubert, M.

1995-12-01

Fundamental results of the possibility of using high temperature superconductors (HTSC) in resistive fault current limiters are discussed. Measurement of the homogeneity of BSCCO-powder-in-tube materials were made. In addition, investigations of the transition from superconducting to normalconducting state under AC-current conditions were carried out. Based on these results, simulations of HTSC-materials on ceramic substrate were made and recent results are presented. Important results of the investigations are: 1. Current-limiting without external trigger only possible when the critical current density of HTSC exceeds 10 4 A/cm 2 . 2. Inhomogeneities sometimes cause problems with local destruction. This can be solved by parallel-elements or external trigger. 3. Fast current-limiting causes overvoltages which can be reduced by using parallel-elements. (orig.) [de

Critical phenomena at perfect and non-perfect surfaces

International Nuclear Information System (INIS)

Pleimling, M

2004-01-01

In the past, perfect surfaces have been shown to yield local critical behaviour that differs from bulk critical behaviour. On the other hand, surface defects, whether they are of natural origin or created artificially, are known to modify local quantities. It is therefore important to clarify whether these defects are relevant or irrelevant for the surface critical behaviour. The purpose of this review is two-fold. In the first part we summarize some of the important results on surface criticality at perfect surfaces. Special attention is thereby paid to new developments such as for example the study of the surface critical behaviour in systems with competing interactions or of surface critical dynamics. In the second part the effect of surface defects (presence of edges, steps, quenched randomness, lines of adatoms, regular geometric patterns) on local critical behaviour in semi-infinite systems and in thin films is discussed in detail. Whereas most of the defects commonly encountered are shown to be irrelevant, some notable exceptions are highlighted. It is shown furthermore that under certain circumstances non-universal local critical behaviour may be observed at surfaces. (topical review)

AC losses in a type II superconductor strip with inhomogeneous critical current distribution

International Nuclear Information System (INIS)

Tsukamoto, Osami

2005-01-01

Analytical formulae derived by Brandt and Indenbom (1993 Phys. Rev. B 48 12893-906) and Norris (1970 J. Phys. D: Appl. Phys. 3 489-507) are often used to calculate the magnetization and AC transport current losses in HTS strip conductors, respectively. In these formulae, homogeneous distribution of critical sheet current density σ c in the strip is assumed. However, it is considered that σ c distributions are inhomogeneous in actual HTS strips and that the inhomogeneous σ c distributions cause deviations of the measured AC loss data of actual HTS strips from those formulae. A semi-analytical method to calculate AC transport current and magnetization losses is derived for a type II superconductor strip with inhomogeneous distribution of σ c in the direction of the strip width. The method is derived modifying the analysis of Brandt et al. The validity of the semi-analytical method is shown by comparing the results calculated by this method with those calculated by the Norris and Brandt formulae and by a different method of our previous work and also with experimental data. Moreover, it is shown that the deviation of the measured data from the Norris and Brandt models can be estimated by assuming proper σ c distributions

Can critical inquiry differ from criticism? A dialogue with current occupational science and occupational therapy schools of inquiry

Directory of Open Access Journals (Sweden)

Jessie Wilson

2016-07-01

Full Text Available Introduction: Critical inquiry has been adopted by various academic disciplines. However, there is a lack of consistency and transparency in the way this complex theoretical and methodological position is applied in research. For novice researchers that ambiguity can lead to blurring the conceptual distinction between critical research and the act of criticizing. Objective: The purpose of this essay is to reflect on what it means to keep a critical perspective for novice researchers. Method: The concepts are explored through a personal narrative that allows authors to examine the details of their trajectory to embrace a critical perspective, which has the power to lead to change, both personal and social. Results: We explore the methodological foundations of the critical research and observe how the emotion is taken over or suppressed in the investigation process. Conclusion: We contextualize key concepts of critical investigation, examining its recent application both in occupational science and in occupational therapy.

Transport measurements in superconductors: critical current of granular high TC ceramic superconductor samples; Medidas de transporte em supercondutores: corrente critica de supercondutores granulares de alta temperatura critica

Energy Technology Data Exchange (ETDEWEB)

Passos, W.A.C., E-mail: wagner.passos@univasf.edu.br [Universidade Federal do Vale do Sao Francisco (IPCM/UNIVASF), Juazeiro do Norte, BA (Brazil). Instituto de Pesquisas em Ciencia dos Materiais; Silva, E.B. [Companhia Energetica do Sao Francisco (CHESF), Recife, PE (Brazil)

2016-07-01

This work presents a method to obtain critical current of granular superconductors. We have carried out transport measurements (ρxT curves and VxI curves) in a YBa{sub 2}Cu{sub 3}O{sub 7-δ} sample to determine critical current density of it. Some specimens reveal a 'semiconductor-like' behavior (electrical resistivity decreases with increasing temperatures above critical temperature T{sub c} of material) competing with superconductor behavior. Due to high granular fraction of the sample, these competition is clearly noted in ρxT curves. Measurements carried out from 0 to 8500 Oe of applied field show the same behavior, and the critical current density of the samples is shown. (author)

Double disordered YBCO coated conductors of industrial scale: high currents in high magnetic field

International Nuclear Information System (INIS)

Abraimov, D; Francis, A; Jaroszynski, J; McCallister, J; Polyanskii, A; Santos, M; Viouchkov, Y L; Ballarino, A; Bottura, L; Rossi, L; Barth, C; Senatore, C; Dietrich, R; Rutt, A; Schlenga, K; Usoskin, A; Majkic, G S; Selvamanickam, V

2015-01-01

A significant increase of critical current in high magnetic field, up to 31 T, was recorded in long tapes manufactured by employing a double-disorder route. In a double-disordered high-temperature superconductor (HTS), a superimposing of intrinsic and extrinsic disorder takes place in a way that (i) the intrinsic disorder is caused by local stoichiometry deviations that lead to defects of crystallinity that serve as pining centers in the YBa 2 Cu 3 O x−δ matrix and (ii) the extrinsic disorder is introduced via embedded atoms or particles of foreign material (e.g. barium zirconate), which create a set of lattice defects. We analyzed possible technological reasons for this current gain. The properties of these tapes over a wider field-temperature range as well as field anisotropy were also studied. Record values of critical current as high as 309 A at 31 T, 500 A at 18 Tm and 1200 A at 5 T were found in 4 mm wide tape at 4.2 K and B perpendicular to tape surface. HTS layers were processed in medium-scale equipment that allows a maximum batch length of 250 m while 22 m long batches were provided for investigation. Abnormally high ratios (up to 10) of critical current density measured at 4.2 K, 19 T to critical current density measured at 77 K, self-field were observed in tapes with the highest in-field critical current. Anisotropy of the critical current as well as angular dependences of n and α values were investigated. The temperature dependence of critical current is presented for temperatures between 4.2 and 40 K. Prospects for the suppression of the dog-bone effect by Cu plating and upscale of processing chain to >500 m piece length are discussed. (paper)

Double disordered YBCO coated conductors of industrial scale: high currents in high magnetic field

Science.gov (United States)

Abraimov, D.; Ballarino, A.; Barth, C.; Bottura, L.; Dietrich, R.; Francis, A.; Jaroszynski, J.; Majkic, G. S.; McCallister, J.; Polyanskii, A.; Rossi, L.; Rutt, A.; Santos, M.; Schlenga, K.; Selvamanickam, V.; Senatore, C.; Usoskin, A.; Viouchkov, Y. L.

2015-11-01

A significant increase of critical current in high magnetic field, up to 31 T, was recorded in long tapes manufactured by employing a double-disorder route. In a double-disordered high-temperature superconductor (HTS), a superimposing of intrinsic and extrinsic disorder takes place in a way that (i) the intrinsic disorder is caused by local stoichiometry deviations that lead to defects of crystallinity that serve as pining centers in the YBa2Cu3O x-δ matrix and (ii) the extrinsic disorder is introduced via embedded atoms or particles of foreign material (e.g. barium zirconate), which create a set of lattice defects. We analyzed possible technological reasons for this current gain. The properties of these tapes over a wider field-temperature range as well as field anisotropy were also studied. Record values of critical current as high as 309 A at 31 T, 500 A at 18 Tm and 1200 A at 5 T were found in 4 mm wide tape at 4.2 K and B perpendicular to tape surface. HTS layers were processed in medium-scale equipment that allows a maximum batch length of 250 m while 22 m long batches were provided for investigation. Abnormally high ratios (up to 10) of critical current density measured at 4.2 K, 19 T to critical current density measured at 77 K, self-field were observed in tapes with the highest in-field critical current. Anisotropy of the critical current as well as angular dependences of n and α values were investigated. The temperature dependence of critical current is presented for temperatures between 4.2 and 40 K. Prospects for the suppression of the dog-bone effect by Cu plating and upscale of processing chain to >500 m piece length are discussed.

Choice of sample size for high transport critical current density in a granular superconductor: percolation versus self-field effects

International Nuclear Information System (INIS)

Mulet, R.; Diaz, O.; Altshuler, E.

1997-01-01

The percolative character of the current paths and the self-field effects were considered to estimate optimal sample dimensions for the transport current of a granular superconductor by means of a Monte Carlo algorithm and critical-state model calculations. We showed that, under certain conditions, self-field effects are negligible and the J c dependence on sample dimensions is determined by the percolative character of the current. Optimal dimensions are demonstrated to be a function of the fraction of superconducting phase in the sample. (author)

Locality of Temperature

Science.gov (United States)

Kliesch, M.; Gogolin, C.; Kastoryano, M. J.; Riera, A.; Eisert, J.

2014-07-01

This work is concerned with thermal quantum states of Hamiltonians on spin- and fermionic-lattice systems with short-range interactions. We provide results leading to a local definition of temperature, thereby extending the notion of "intensivity of temperature" to interacting quantum models. More precisely, we derive a perturbation formula for thermal states. The influence of the perturbation is exactly given in terms of a generalized covariance. For this covariance, we prove exponential clustering of correlations above a universal critical temperature that upper bounds physical critical temperatures such as the Curie temperature. As a corollary, we obtain that above the critical temperature, thermal states are stable against distant Hamiltonian perturbations. Moreover, our results imply that above the critical temperature, local expectation values can be approximated efficiently in the error and the system size.

Critical Values for Yen’s Q₃

DEFF Research Database (Denmark)

Christensen, Karl Bang; Makransky, Guido; Horton, Mike

2017-01-01

The assumption of local independence is central to all item response theory (IRT) models. Violations can lead to inflated estimates of reliability and problems with construct validity. For the most widely used fit statistic Q3, there are currently no well-documented suggestions of the critical...... to the data set, and provide example critical values for a number of data structure situations. The results show that for the Q3 fit statistic, no single critical value is appropriate for all situations, as the percentiles in the empirical null distribution are influenced by the number of items, the sample...... size, and the number of response categories. Furthermore, the results show that LD should be considered relative to the average observed residual correlation, rather than to a uniform value, as this results in more stable percentiles for the null distribution of an adjusted fit statistic....

The low-temperature, high-magnetic-field critical current characteristics of Zr-added (Gd, Y)Ba2Cu3Ox superconducting tapes

Energy Technology Data Exchange (ETDEWEB)

Selvamanickam, V; Yao, Y; Chen, Y; Shi, T; Liu, Y; Khatri, ND; Liu, J; Lei, C; Galstyan, E; Majkic, G

2012-10-26

Critical current performances of state-of-the-art Zr-added (Gd, Y)BaCuO tapes have been investigated over a temperature range of 20-77 K, in magnetic fields up to 9 T and over a wide angular range of magnetic field orientations. The peak in critical current that is commonly observed in the field orientation perpendicular to the tape in BaZrO3 (BZO) containing superconducting tapes is found to vanish at 30 K in magnetic fields at 1-9 T. While the critical current of 15% Zr-added tapes was about 40% lower than that of 7.5% Zr-added tapes at 77 K, the pinning force values of the former were found to be 18-23% higher than those of the latter in the temperature range of 20-40 K and in magnetic fields of 3-5 T. The results from this study emphasize the importance of optimization of coated conductor fabrication processes for optimum performance not just in low magnetic fields at 77 K but also at the operating conditions of low temperatures and high magnetic fields that are of interest, especially for rotating superconducting machinery applications.

The low-temperature, high-magnetic-field critical current characteristics of Zr-added (Gd,Y)Ba2Cu3Ox superconducting tapes

International Nuclear Information System (INIS)

Selvamanickam, V; Yao, Y; Shi, T; Liu, Y; Khatri, N D; Liu, J; Galstyan, E; Majkic, G; Chen, Y; Lei, C

2012-01-01

Critical current performances of state-of-the-art Zr-added (Gd, Y)BaCuO tapes have been investigated over a temperature range of 20–77 K, in magnetic fields up to 9 T and over a wide angular range of magnetic field orientations. The peak in critical current that is commonly observed in the field orientation perpendicular to the tape in BaZrO 3 (BZO) containing superconducting tapes is found to vanish at 30 K in magnetic fields at 1–9 T. While the critical current of 15% Zr-added tapes was about 40% lower than that of 7.5% Zr-added tapes at 77 K, the pinning force values of the former were found to be 18–23% higher than those of the latter in the temperature range of 20–40 K and in magnetic fields of 3–5 T. The results from this study emphasize the importance of optimization of coated conductor fabrication processes for optimum performance not just in low magnetic fields at 77 K but also at the operating conditions of low temperatures and high magnetic fields that are of interest, especially for rotating superconducting machinery applications. (paper)

Local Agenda 21 is not a group

DEFF Research Database (Denmark)

Hoffmann, Birgitte

1999-01-01

The article is a critical overview of the Danish approach to Local Agenda 21. It states Local Agenda 21 as a tool for the process of change.......The article is a critical overview of the Danish approach to Local Agenda 21. It states Local Agenda 21 as a tool for the process of change....

The potential of mobile phones for increasing public participation in local government in South Africa

Directory of Open Access Journals (Sweden)

Hannah Thinyane

2015-12-01

Full Text Available This paper presents a critical discussion on the current use of technology and participation in local government. It discusses the rise in popularity of mobile devices, and how they have been used in ICT for development. The paper describes the results of a baseline study undertaken in a city within Makana Municipality in the Eastern Cape of South Africa, to empirically investigate how residents are currently using mobile phones and participating with local government around the area of service delivery. The findings illustrate the current state of mobile phone usage and capabilities, and the potential for using the mobile platform to increase participation in local government in South Africa. The paper also can be used to inform and guide project stakeholders on how best to implement m-participation strategies.

Characterizing agosticity using the quantum theory of atoms in molecules: bond critical points and their local properties.

Science.gov (United States)

Tognetti, Vincent; Joubert, Laurent; Raucoules, Roman; De Bruin, Theodorus; Adamo, Carlo

2012-06-07

In this paper, we extend the work of Popelier and Logothetis [J. Organomet. Chem. 1998, 555, 101] on the characterization of agosticity by considerably enlarging the set of the studied organometallic molecules. To this aim, 23 representative complexes have been considered, including all first line transition metals at various oxidation states and exhibiting four types of agosticity (α, β, γ, and δ). From these examples, the concepts of agostic atom, agostic bond, and agostic interaction are defined and discussed, notably by advocating Bader's analysis of the electron density. The nature and the local properties of the bond critical points are then investigated, and the relationships with the main geometric parameters of the complexes are particularly examined. Moreover, new local descriptors based on kinetic energy densities are developed in order to provide new tools for bond characterization.

Local anesthetics for brain tumor resection: Current perspectives

NARCIS (Netherlands)

J.W. Potters (Jan Willem); M. Klimek (Markus)

2018-01-01

textabstractThis review summarizes the added value of local anesthetics in patients undergoing craniotomy for brain tumor resection, which is a procedure that is carried out frequently in neurosurgical practice. The procedure can be carried out under general anesthesia, sedation with local

Petroleum Scarcity and Public Health: Considerations for Local Health Departments

Science.gov (United States)

Parker, Cindy L.; Caine, Virginia A.; McKee, Mary; Shirley, Lillian M.; Links, Jonathan M.

2011-01-01

Recognition of petroleum as a finite global resource has spurred increasing interest in the intersection between petroleum scarcity and public health. Local health departments represent a critical yet highly vulnerable component of the public health infrastructure. These frontline agencies currently face daunting resource constraints and rely heavily on petroleum for vital population-based health services. Against this backdrop, petroleum scarcity may necessitate reconfiguring local public health service approaches. We describe the anticipated impacts of petroleum scarcity on local health departments, recommend the use of the 10 Essential Public Health Services as a framework for examining attendant operational challenges and potential responses to them, and describe approaches that local health departments and their stakeholders could consider as part of timely planning efforts. PMID:21778471

Chen-Nester-Tung quasi-local energy and Wang-Yau quasi-local mass

Science.gov (United States)

Liu, Jian-Liang; Yu, Chengjie

2017-10-01

In this paper, we show that the Chen-Nester-Tung (CNT) quasi-local energy with 4D isometric matching references is closely related to the Wang-Yau (WY) quasi-local energy. As a particular example, we compute the second variation of the CNT quasi-local energy for axially symmetric Kerr-like spacetimes with axially symmetric embeddings at the obvious critical point (0 , 0) and find that it is a saddle critical point in most of the cases. Also, as a byproduct, we generalize a previous result about the coincidence of the CNT quasi-local energy and Brown-York mass for axially symmetric Kerr-like spacetimes by Tam and the first author Liu and Tam (2016) to general spacetimes.

Local and social facets of planetary boundaries: right to nutrients

International Nuclear Information System (INIS)

Kahiluoto, Helena; Kuisma, Miia; Kuokkanen, Anna; Mikkilä, Mirja; Linnanen, Lassi

2015-01-01

Anthropogenic nutrient flows exceed the planetary boundaries. The boundaries and the current excesses vary spatially. Such variations have both an ecological and a social facet. We explored the spatial variation using a bottom-up approach. The local critical boundaries were determined through the current or accumulated flow of the preceding five years before the planetary boundary criteria were met. Finland and Ethiopia served as cases with contrasting ecology and wealth. The variation in excess depends on historical global inequities in the access to nutrients. Globally, the accumulated use per capita is 2300 kg reactive nitrogen (N r ) and 200 kg phosphorus (P). For Finland, the accumulated use per capita is 3400 kg N r and 690 kg P, whereas for Ethiopia, it is 26 kg N r and 12 kg P. The critical N boundary in Finland is currently exceeded by 40 kg cap −1 a −1 and the accumulated excess is 65 kg cap −1 a −1 , while the global current excess is 24 kg cap −1 a −1 and there is space in Ethiopia to increase even the accumulated flow. The critical P boundary is exceeded in Finland and (although less so) in Ethiopia, but for contrary reasons: (1) the excessive past inflow to the agrifood system in Finland and (2) the excessive outflow from the agrifood system triggered by deficits in inflow and waste management in Ethiopia. The critical boundaries set by Finnish marine systems are lower and those set by freshwaters are higher than the planetary boundaries downscaled per capita. The shift to dominance of internal loading in watercourses represents a tipping point. We conclude that food security within the safe boundaries requires global redistribution of nutrients in residues, soils and sediments and of rights to use nutrients. Bottom-up assessments reveal local dynamics that shed new light on the relevant boundary criteria and on estimates and remedies. (letter)

Local regulation of interchange turbulence in a dipole-confined plasma torus using current-collection feedback

International Nuclear Information System (INIS)

Roberts, T. M.; Mauel, M. E.; Worstell, M. W.

2015-01-01

Turbulence in plasma confined by a magnetic dipole is dominated by interchange fluctuations with complex dynamics and short spatial coherence. We report the first use of local current-collection feedback to modify, amplify, and suppress these fluctuations. The spatial extent of turbulence regulation is limited to a correlation length near the collector. Changing the gain and phase of collection results in power either extracted from or injected into the turbulence. The measured plasma response shows some agreement with calculations of the linear response of global interchange-like MHD and entropy modes to current-collection feedback

Experimental study of flux pinning in NbN films and multilayers: Ultimate limits on critical currents in superconductors

International Nuclear Information System (INIS)

Gray, K.E.; Kampwirth, R.T.; Capone, D.W. II; Murduck, J.M.

1988-08-01

A flux pinning model is presented which predicts the maximum critical current density attainable in superconductors. That such a limit must exist comes from the realization that flux pinning is strongest in regions of weak superconductivity, but these regions cannot carry a large supercurrent. Since the same regions within the superconductor cannot be used for both pinning and supercurrent conductions, there must be an optimum mix, leading to a maximum J/sub c/. Measurements on films and multilayers of NbN have verified many details of the model including anisotropy effects and a strong reduction in J/sub c/ for defect spacings smaller than the flux core diameter. In an optimized multilayer the pinning force reached /approximately/22% of the theoretical maximum. The implications of these results on the practical applications of NbN films and on the maximum critical current density in the new high temperature superconductors are also discussed. 24 refs., 4 figs

Investigation of local heterogeneity of hbO2 and hb in working dog heart in situ under isovolemic hemodilution and critical coronary stenosis

Science.gov (United States)

Krug, Alfons; Kessler, Manfred D.; Khuri, Raja; Lust, Robert; Chitwood, Randolph

1996-12-01

A tissue spectrophotometer (EMPHO II) working with 70 micrometer micro lightguide sensors enables recording of spectra in the visible wavelength range (500 - 630 nm). During an initial period arterial hypoxia and hyperoxia were induced on working dog heart by mechanical ventilation with oxygen fractions (fiO2) of 0.1 and 0.5. Under these conditions the effects of low and high fiO2 on oxygenation distribution of intracapillary hemoglobin were investigated. In the second part of the experiment the relation between systemic hematocrit, local hemoglobin concentration, local hemoglobin oxygenation and the oxygen regulation mechanism were studied in detail. In the final part of the experiment the effect of critical coronary stenosis on hb and hbO2 was measured. Critical stenosis was achieved by partial clamping of the left anterior coronary artery (LAD).

Electromagnetic particle in cell modeling of the plasma focus: Current sheath formation and lift off

International Nuclear Information System (INIS)

Seng, Y. S.; Lee, P.; Rawat, R. S.

2014-01-01

The shaping and formation of the current sheath takes place in the breakdown phase of a plasma focus device and critically controls the device performance. Electrostatic particle in cell codes, with magnetic effects ignored, have been used to model the breakdown phase. This Letter reports the successful development and implementation of an electromagnetic particle in cell (EMPIC) code, including magnetic effects self-consistently, to simulate the breakdown phase; from the ionization, localization and gliding discharge along the insulator to the time instant of current sheath lift off. The magnetic field was found to be appreciable from the time the current sheath came into contact with the anode with increased local current, initiating the voltage breakdown of the device as a result

Effect of 520 MeV Kr{sup 20+} ion irradiation on the critical current density of Bi-2212 single crystals

Energy Technology Data Exchange (ETDEWEB)

Terai, Takayuki; Ito, Yasuyuki [Tokyo Univ. (Japan). Faculty of Engineering; Kishio, Kouji

1996-10-01

Change in magnetic properties of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+y} (Bi-2212) single crystals due to Kr{sup 20+} ion irradiation is reported, focused on critical current density and irreversibility magnetic field. The Bi-2212 single crystal specimens (3x3x0.3 mm{sup 3}) were prepared by the floating zone method. Each specimen was irradiated with 520 MeV Kr{sup 20+} ions of 10{sup 10}-10{sup 11} cm{sup -2} in the fluence. Magnetic hysteresis was measured at 4.2K-60K with a vibrating sample magnetometer before and after irradiation. Very large enhancement was observed in critical current density and irreversibility magnetic field above 20K. (author)

Detection of localized damage by eddy currents technique

Directory of Open Access Journals (Sweden)

Aoukili A.

2014-01-01

Full Text Available Non destructive evaluation techniques based on eddy currents (EC are largely used for quality control of the castings in a lot of industries. The principle of detection by EC consists in using an adequate inductive coil to generate them by a variable magnetic field, and measuring their effects by using one or several sensors. These effects result from the interaction between the induced magnetic field and the excited conductive material. A local variation of the physical properties or geometry of the tested sample, due to a singularity or a flaw, causes a modification of the EC distribution, enabling thus detection. In order to optimize the capacity of defect revealing by means of EC based probes, an accurate modelling of the problem is essential. This can be used to perform simulation of the EC distribution under different circumstances and to analyze the EC sensitivity to the various implicated parameters. In this work, the modelling of EC is made by using the finite element method. Using a B-scan strategy was used, detection of a small defect having the shape of an open cavity is shown to be correctly indicated via monitoring variations of the induced voltage in the receiver coil.

Direct observation of current in type-I edge-localized-mode filaments on the ASDEX upgrade tokamak

DEFF Research Database (Denmark)

Vianello, N.; Zuin, M.; Cavazzana, R.

2011-01-01

Magnetically confined plasmas in the high confinement regime are regularly subjected to relaxation oscillations, termed edge localized modes (ELMs), leading to large transport events. Present ELM theories rely on a combined effect of edge current and the edge pressure gradients which result...

Current trials to reduce surgical intervention in ductal carcinoma in situ of the breast: Critical review.

Science.gov (United States)

Toss, M; Miligy, I; Thompson, A M; Khout, H; Green, A R; Ellis, I O; Rakha, E A

2017-10-01

The high proportion of ductal carcinoma in situ (DCIS) presented in mammographic screening and the relatively low risk of progression to invasive disease have raised questions related to overtreatment. Following a review of current DCIS management protocols a more conservative approach has been suggested. Clinical trials have been introduced to evaluate the option of avoiding surgical intervention in a proportion of patients with DCIS defined as "low-risk" using certain clinicopathological criteria. These trials can potentially provide evidence-based models of active surveillance (with or without endocrine therapy) as a future management approach. Despite the undisputable fact of our need to address the obvious overtreatment of screen-detected DCIS, some important questions need to be considered regarding these trials including the eligibility criteria and definition of risk, the proportion of patient eligible for inclusion, and the length of time required for proper analysis of the trials' outcome in view of the long-term natural history of DCIS progression particularly the low-risk group. These factors can potentially affect the practicality and future impact of such trials. This review provides critical analysis of current DCIS management trials and highlights critical issues related to their practicality and the expected outcome. Copyright © 2017 Elsevier Ltd. All rights reserved.

Magnetic properties and critical current density of bulk MgB2 polycrystalline with Bi-2212 addition

International Nuclear Information System (INIS)

Shen, T M; Li, G; Zhu, X T; Cheng, C H; Zhao, Y

2005-01-01

Bulk samples of MgB 2 were prepared with 0, 3, 5, and 10 wt% Bi 2 Sr 2 CaCu 2 O 8 (Bi-2212) particles, added using a simple solid-state reaction route in order to investigate the effect of inclusions of a material with higher T c than the superconducting matrix. The density, diamagnetic signal, and critical current density, J c , of the samples change significantly with the doping level. It is found that J c is significantly enhanced by the Bi-2212 addition. Microstructural analysis indicates that a small amount of Bi-2212 is decomposed into Cu 2 O and other impurity phases while a significant amount of unreacted Bi-2212 particles remains in MgB 2 matrix, and these act as effective pinning centres for vortices. The enhanced pinning force is mainly attributable to these highly dispersed inclusions inserted in the MgB 2 grains. Despite the effectiveness of the high-T c inclusions in increasing superconducting critical currents in our experiment, our results seem to demonstrate the superiority of attractive centres over repulsive ones. A pinning mechanism is proposed to account for the contribution of this type of pinning centre in MgB 2 superconductors. (rapid communication)

Current status and perceived needs of information technology in Critical Access Hospitals: a survey study

Directory of Open Access Journals (Sweden)

George Demiris

2007-01-01

Full Text Available The US Congress established the designation of Critical Access Hospitals in 1997, recognising rural hospitals as vital links to health for rural and underserved populations. The intent of the reimbursement system is to improve financial performance, thereby reducing hospital closures. Informatics applications are thought to be tools that can enable the sustainability of such facilities. The aim of this study is to identify the current use of information and communication technology in Critical Access Hospitals, and to assess their readiness and receptiveness for the use of new software and hardware applications and their perceived information technology (IT needs. A survey was mailed to the administrators of all Critical Access Hospitals in one US state (Missouri and a reminder was mailed a few weeks later. Twenty-seven out of 33 surveys were filled out and returned (response rate 82%. While most respondents (66.7% stated that their employees have been somewhat comfortable in using new technology, almost 15% stated that their employees have been somewhat uncomfortable. Similarly, almost 12% of the respondents stated that they themselves felt somewhat uncomfortable introducing new technology. While all facilities have computers, only half of them have a specific IT plan. Findings indicate that Critical Access Hospitals are often struggling with lack of resources and specific applications that address their needs. However, it is widely recognised that IT plays an essential role in the sustainability of their organisations. The study demonstrates that IT applications have to be customised to address the needs and infrastructure of the rural settings in order to be accepted and properly utilised.

High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

Energy Technology Data Exchange (ETDEWEB)

Selvamanickam, V; Gharahcheshmeh, MH; Xu, A; Galstyan, E; Delgado, L; Cantoni, C

2015-01-19

REBa2Cu3Ox ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50K and fields of 2-30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J(c)) above 20 MA/cm(2) at 30 K, 3 T in heavily doped (25 mol.% Zr-added) (Gd,Y)Ba2Cu3Ox superconductor tapes, which is more than three times higher than the J(c) typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m(3) have also been attained at 20 K. A composition map of lift factor in J(c) (ratio of J(c) at 30 K, 3 T to the J(c) at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO3 (BZO) nanocolumn defect density of nearly 7 x 10(11) cm(-2) as well as 2-3 nm sized particles rich in Cu and Zr have been found in the high J(c) films. (C) 2015 AIP Publishing LLC.

Critical Josephson current in a model Pb/YBa2Cu3O7-δ junction

International Nuclear Information System (INIS)

Atkinson, W.A.; Carbotte, J.P.

1995-01-01

We consider a simple model for a c-axis Pb/YBa 2 Cu 3 O 7-δ Josephson junction. The observation of a nonzero current in such a junction by Sun et al. [Phys. Rev. Lett. 72, 2267 (1994)] has been taken as evidence against d-wave superconductivity in YBa 2 Cu 3 O 7-δ . We suggest, however, that the pairing interaction in the CuO 2 planes may well be d wave but that the CuO chains destroy the tetragonal symmetry of the system. We examine two ways in which this happens. In a simple model of an incoherent junction, the chains distort the superconducting condensate away from d x 2 -y 2 symmetry. In a specular junction the chains destroy the tetragonal symmetry of the tunneling matrix element. In either case, the loss of tetragonal symmetry results in a finite Josephson current. Our calculated values of the critical current for specular junctions are in good agreement with the results of Sun and co-workers

Non-equilibrium properties of Josephson critical current in Nb-based three terminal superconducting tunnel devices

International Nuclear Information System (INIS)

Ammendola, G.; Parlato, L.; Peluso, G.; Pepe, G.

1998-01-01

Tunnel quasi-particle injection into a superconducting film provides useful information on the non-equilibrium state inside the perturbed superconductor as well as on the potential application to electronic devices. Three terminal injector-detector superconducting devices have a long history in non-equilibrium superconductivity. In the recent past non-equilibrium phenomena have attracted again considerable attention because of many superconducting based detectors involve processes substantially non-equilibrium in nature. The possibility of using a stacked double tunnel junction to study the influence of non-equilibrium superconductivity on the Josephson critical current is now considered. An experimental study of the effect of quasi-particle injection on the Josephson current both in steady-state and pulsed experiments down to T=1.2 K is presented using 3 terminal Nb-based stacked double tunnel devices. The feasibility of a new class of particle detectors based on the direct measurement of the change in the Josephson current following the absorption of a X-ray quantum is also discussed in terms of non-equilibrium theories. (orig.)

Metatheoretical critics on current trends in Quantum Mechanics

Directory of Open Access Journals (Sweden)

Carlos C. Aranda

2014-06-01

Full Text Available Is our purpose in this article to review several approaches to modern problems in quantum mechanics from a critical point of view using the approximation of the traditional mathematical thinking. Nevertheless we point out several natural questions that arise in abstract mathematical reasoning.

Detecting many-body-localization lengths with cold atoms

Science.gov (United States)

Guo, Xuefei; Li, Xiaopeng

2018-03-01

Considering ultracold atoms in optical lattices, we propose experimental protocols to study many-body-localization (MBL) length and criticality in quench dynamics. Through numerical simulations with exact diagonalization, we show that in the MBL phase the perturbed density profile following a local quench remains exponentially localized in postquench dynamics. The size of this density profile after long-time-dynamics defines a localization length, which tends to diverge at the MBL-to-ergodic transition as we increase the system size. The determined localization transition point agrees with previous exact diagonalization calculations using other diagnostics. Our numerical results provide evidence for violation of the Harris-Chayes bound for the MBL criticality. The critical exponent ν can be extracted from our proposed dynamical procedure, which can then be used directly in experiments to determine whether the Harris-Chayes-bound holds for the MBL transition. These proposed protocols to detect localization criticality are justified by benchmarking to the well-established results for the noninteracting three-dimensional Anderson localization.

Progress in American Superconductor’s HTS wire and optimization for fault current limiting systems

Energy Technology Data Exchange (ETDEWEB)

Malozemoff, Alexis P., E-mail: amalozemoff@amsc.com

2016-11-15

Highlights: • AMSC HTS wire critical current needed for rotating machinery is doubled by 16 MeV Au irradiation. • Nonuniformity of HTS wires in power devices causes hot spot formation during power system faults. • Lower normal-state resistivity and critical current lower HTS wire hot spot heating during faults. • HTS wire hot spot heating in HTS cables during faults must stay below lN{sub 2} bubble nucleation point. • HTS wire can be designed to meet hot spot heating limits in fault current limiting cables. - Abstract: American Superconductor has developed composite coated conductor tape-shaped wires using high temperature superconductor (HTS) on a flexible substrate with laminated metal stabilizer. Such wires enable many applications, each requiring specific optimization. For example, coils for HTS rotating machinery require increased current density J at 25–50 K. A collaboration with Argonne, Brookhaven and Los Alamos National Laboratories and several universities has increased J using an optimized combination of precipitates and ion irradiation defects in the HTS. Major commercial opportunities also exist to enhance electric power grid resiliency by linking substations with distribution-voltage HTS power cables [10]. Such links provide alternative power sources if one substation's transmission-voltage power is compromised. But they must also limit fault currents which would otherwise be increased by such distribution-level links. This can be done in an HTS cable, exploiting the superconductor-to-resistive transition when current exceeds the wires’ critical J. A key insight is that such transitions are usually nonuniform; so the wire must be designed to prevent localized hot spots from damaging the wire or even generating gas bubbles in the cable causing dielectric breakdown. Analysis shows that local heating can be minimized by increasing the composite tape's total thickness, decreasing its total resistance in the normal state and

Development of inherent technologies for advanced PWR core - A study on the current status and the construction feasibility of critical facilities

Energy Technology Data Exchange (ETDEWEB)

Yang, Won Sik; Yang, Hyun Seok [Chosun University, Kwangju (Korea); Kim, Chang Hyo; Shim, Hyung Jin [Seoul National University, Seoul (Korea)

1999-03-01

The objective of this study is to examine the appropriateness of constructing critical facilities in our country and to decide a course of constructing them if necessary by surveying the status and utilization of foreign facilities and by investigating the demand for domestic facilities. We investigated the status and the utilization of foreign critical facilities through literature survey and personal visitation. In our judgement, critical facilities are necessary for developing the advanced reactors and fuels which are being studied as parts of the Nuclear R and D Program by MOST. Considering the construction cost and the current state of domestic economy, however, it is unjustifiable to build three different types of critical facilities (the light water, the heavy water, and the fast critical facility). It appears to be reasonable to build a light water critical, considering the construction cost, degree of utilization, and other constraints. (author). 89 refs., 134 figs., 64 tabs.

Correlation between in-field critical currents in Zr-added (Gd, Y)Ba2Cu3Ox superconducting tapes at 30 and 77 K

International Nuclear Information System (INIS)

Selvamanickam, V; Xu, A; Liu, Y; Khatri, N D; Galstyan, E; Majkic, G; Lei, C; Chen, Y

2014-01-01

Critical current (I c ) values of 1384 A/12 mm, corresponding to a critical current density of 12.47 MA cm −2 and a pinning force of 374 GN m −3 , have been achieved at 30 K, 3 T in the orientation of field parallel to the c axis (B ∥ c) in (Gd, Y)BaCuO tapes with 15 mol% Zr addition made by metal organic chemical vapor deposition (MOCVD). These tapes show pinning force levels as high as 453 GN m −3 at 30 K. An analysis of the properties of 24–28 (Gd, Y)BaCuO tapes with 15 mol% Zr addition showed a lack of correlation between their critical currents at 30 K, 3 T (B ∥ c) and I c values both at 77 K, zero field and at 77 K, 1 T (B ∥ c). However, a strong correlation was found between the critical currents at 30 K, 3 T and at 77 K, 3 T (B ∥ c). It has also been discovered that the minimum critical current (I c, min ) value at 77 K, 3 T has no influence on the I c, min value at 30 K, 3 T, and it in turn depends on the ratio of the I c values in the orientations of field parallel and perpendicular to the c axis at 77 K, 3 T. (paper)

Influence of vanadium substitution on structure and critical currents of YBa2Cu3O7-δ

International Nuclear Information System (INIS)

Jadhav, K.M.; Raibagkar, R.L.

1995-01-01

V-doped YBa 2 Cu 3 O 7-δ samples prepared under identical conditions have been investigated by magnetization measurements as a function of temperature and field. The critical current density, J c has been deduced from the hysteresis data, using the appropriate field window within which a linear relationship between ΔM(H) and J c is valid. (author). 7 refs., 4 figs., 1 tab

Combined local current distribution measurements and high resolution neutron radiography of operating direct methanol fuel cells

Energy Technology Data Exchange (ETDEWEB)

Schroeder, Alexander; Wippermann, Klaus [Forschungszentrum Juelich GmbH (Germany). Inst. of Energy Research, IEF-3: Fuel Cells; Sanders, Tilman [RWTH Aachen (DE). Inst. for Power Electronics and Electrical Drives (ISEA); Arlt, Tobias [Helmholtz Centre Berlin (Germany). Inst. for Applied Materials

2010-07-01

Neutron radiography allows the investigation of the local fluid distribution in direct methanol fuel cells (DMFCs) under operating conditions. Spatial resolutions in the order of some tens of micrometers at the full test cell area are achieved. This offers the possibility to study practice-oriented, large stack cells with an active area of several hundred cm{sup 2} as well as specially designed, small test cells with an area of some cm{sup 2}. Combined studies of high resolution neutron radiography and segmented cell measurements are especially valuable, because they enable a correlation of local fluid distribution and local performance [1, 2]. The knowledge of this interdependency is essential to optimise the water management and performance respecting a homogeneous fluid, current and temperature distribution and to achieve high performance and durability of DMFCs. (orig.)

Effect of the microscopic correlated-pinning landscape on the macroscopic critical current density in YBCO films

Science.gov (United States)

Ghigo, G.; Chiodoni, A.; Gerbaldo, R.; Gozzelino, L.; Laviano, F.; Mezzetti, E.; Minetti, B.; Camerlingo, C.

This paper deals with the mechanisms controlling the critical current density vs. field behavior in YBCO films. We base our analysis on a suitable model concerning the existence of a network of intergrain Josephson junctions whose length is modulated by defects. Irradiation with 0.25 GeV Au ions provide a useful tool to check the texture of the sample, in particular to give a gauge length reference to separate “weak” links and high- J c links.

Development of Nb3Sn cabled conductor by external diffusion process and the effect of strain on the critical current

International Nuclear Information System (INIS)

Pasztor, G.; Ekin, J.W.

1984-01-01

The planned extension of the High Field Test Facility SULTAN at SIN to provide 12 T operation in a 60 cm bore has led to an increased involvements on the part of SIN in the development of reliable A15 multifilamentary conductors. It is the purpose of this paper to describe the development of stranded Nb 3 Sn conductors using the external diffusion technique. Although not fully optimized, the primary cables have high overall critical current densities. Problems associated with the diffusion of the tin into the copper matrix, such as tin coalescence and development of Kirkendall porosity were successfully solved using small diameter wires and by appropriate diffusion and reaction heat treatment conditions. The elastic strain sensitivity of the critical current of a previously developed cable was comparable to that of bronze processed monolithic Nb 3 Sn, while the irreversible strain limit of 1.2% was significantly higher, On the other hand a longer current transfer length (about 4 times that of bronze processed monolithic conductors) was found

The dependence of critical current density of GdFeCo layer on composition of thermally assisted STT-RAM

Science.gov (United States)

Dai, B.; Zhu, J.; Liu, K.; Yang, L.; Han, J.

2017-07-01

Amorphous rare earth-transitional metal (RETM) GdFeCo memory layer with RE- and TM-rich compositions was fabricated in stacks of GdFeCo (10 nm)/Cu (3 nm)/[Co(0.2 nm)/Pd(0.4 nm)]6. Their magnetic properties and spin transfer torque (STT) switching of magnetization were investigated. The maximum magneto-resistance (MR) was around 0.24% for the TM-rich Gd21.4 (Fe90Co10)78.6 memory layer and was -0.03% for the RE-rich Gd29.0 (Fe90Co10)71.0 memory layer. The critical current densities Jc to switch the GdFeCo memory layers are in the range of 1.4 × 107 A/cm2-4.5 × 107 A/cm2. The dependence of critical current density Jc and effective anisotropy constant Keff on Gd composition were also investigated. Both Jc and Keff have maximum values in the Gd composition range from 21-29 at.%, suitable for thermally assisted STT-RAM for storage density exceeding Gb/inch2.

Scapulothoracic bursitis and snapping scapula syndrome: a critical review of current evidence.

Science.gov (United States)

Warth, Ryan J; Spiegl, Ulrich J; Millett, Peter J

2015-01-01

Symptomatic scapulothoracic disorders, such as painful scapular crepitus and/or bursitis, are uncommon; however, they can produce significant pain and disability in many patients. To review the current knowledge pertaining to snapping scapula syndrome and to identify areas of further research that may be helpful to improve clinical outcomes and patient satisfaction. Systematic review. We performed a preliminary search of the PubMed and Embase databases using the search terms "snapping scapula," "scapulothoracic bursitis," "partial scapulectomy," and "superomedial angle resection" in September 2013. All nonreview articles related to the topic of snapping scapula syndrome were included. The search identified a total of 167 unique articles, 81 of which were relevant to the topic of snapping scapula syndrome. There were 36 case series of fewer than 10 patients, 16 technique papers, 11 imaging studies, 9 anatomic studies, and 9 level IV outcomes studies. The level of evidence obtained from this literature search was inadequate to perform a formal systematic review or meta-analysis. Therefore, a critical review of current evidence is presented. Snapping scapula syndrome, a likely underdiagnosed condition, can produce significant shoulder dysfunction in many patients. Because the precise origin is typically unknown, specific treatments that are effective for some patients may not be effective for others. Nevertheless, bursectomy with or without partial scapulectomy is currently the most effective primary method of treatment in patients who fail nonoperative therapy. However, many patients experience continued shoulder disability even after surgical intervention. Future studies should focus on identifying the modifiable factors associated with poor outcomes after operative and nonoperative management for snapping scapula syndrome in an effort to improve clinical outcomes and patient satisfaction. © 2014 The Author(s).

[Critical evaluation of current diagnostic classification systems in psychiatry: the case of DSM-5].

Science.gov (United States)

Luciano, Mario; Sampogna, Gaia; Del Vecchio, Valeria; De Rosa, Corrado; Albert, Umberto; Carrà, Giuseppe; Dell'Osso, Bernardo; Lorenzo, Giorgio Di; Ferrari, Silvia; Martinotti, Giovanni; Nanni, Maria Giulia; Pinna, Federica; Pompili, Maurizio; Volpe, Umberto; Catapano, Francesco; Fiorillo, Andrea

2016-01-01

Since its first edition, the Diagnostic and Statistical manual of Mental disorders (DSM) has had a great impact on the scientific community and the public opinion as well. In 2013, the American Psychiatric Association released the fifth edition of the manual and - as for the previous versions - several criticisms raised. In particular, the persistence of the categorical approach to mental disorders represents one of the main debated topics, as well as the introduction of new diagnostic syndromes, which are not based on an adequate evidences. Moreover, the threshold of diagnostic criteria for many mental disorders has been lowered, with the consequence that the boundaries between "normality" and "pathology" is not so clear. In this paper, we will: 1) report the historical development of the DSM from the publication of its first edition; 2) describe the main changes introduced in the DSM-5; 3) discuss critical elements in the DSM-5. The current debate regarding the validity of diagnostic manuals and its criteria is threatening the psychiatric discipline, but a possible solution should be represented by the integration of diagnostic criteria with the in-depth description of patient's psychopathological experiences.

Evidence for length-dependent wire expansion, filament dedensification and consequent degradation of critical current density in Ag-alloy sheathed Bi-2212 wires

International Nuclear Information System (INIS)

Malagoli, A; Lee, P J; Jiang, J; Trociewitz, U P; Hellstrom, E E; Larbalestier, D C; Ghosh, A K; Scheuerlein, C; Di Michiel, M

2013-01-01

It is well known that longer Bi-2212 conductors have significantly lower critical current density (J c ) than shorter ones, and recently it has become clear that a major cause of this reduction is internal gas pressure generated during heat treatment, which expands the wire diameter and dedensifies the Bi-2212 filaments. Here we report on the length-dependent expansion of 5–240 cm lengths of state-of-the-art, commercial Ag alloy sheathed Bi-2212 wire after full and some partial heat treatments. Detailed image analysis along the wire length shows that the wire diameter increases with distance from the ends, longer samples often showing evident damage and leaks provoked by the internal gas pressure. Comparison of heat treatments carried out just below the melting point and with the usual melt process makes it clear that melting is crucial to developing high internal pressure. The decay of J c away from the ends is directly correlated to the local wire diameter increase, which decreases the local Bi-2212 filament mass density and lowers J c , often by well over 50%. It is clear that control of the internal gas pressure is crucial to attaining the full J c of these very promising round wires and that the very variable properties of Bi-2212 wires are due to the fact that this internal gas pressure has so far not been well controlled. (paper)

RAPID COMMUNICATION: Effect of strain, magnetic field and field angle on the critical current density of Y Ba2Cu3O7-δ coated conductors

Science.gov (United States)

van der Laan, D. C.; Ekin, J. W.; Douglas, J. F.; Clickner, C. C.; Stauffer, T. C.; Goodrich, L. F.

2010-07-01

A large, magnetic-field-dependent, reversible reduction in critical current density with axial strain in Y Ba2Cu3O7-δ coated conductors at 75.9 K has been measured. This effect may have important implications for the performance of Y Ba2Cu3O7-δ coated conductors in applications where the conductor experiences large stresses in the presence of a magnetic field. Previous studies have been performed only under tensile strain and could provide only a limited understanding of the in-field strain effect. We now have constructed a device for measuring the critical current density as a function of axial compressive and tensile strain and applied magnetic field as well as magnetic field angle, in order to determine the magnitude of this effect and to create a better understanding of its origin. The reversible reduction in critical current density with strain becomes larger with increasing magnetic field at all field angles. At 76 K the critical current density is reduced by about 30% at - 0.5% strain when a magnetic field of 5 T is applied parallel to the c-axis of the conductor or 8 T is applied in the ab-plane, compared to a reduction of only 13% in self-field. Differences in the strain response of the critical current density at various magnetic field angles indicate that the pinning mechanisms in Y Ba2Cu3O7-δ coated conductors are uniquely affected by strain. Contribution of NIST, not subject to US copyright.

Nonlinear response of a neoclassical four-field magnetic reconnection model to localized current drive

International Nuclear Information System (INIS)

Lazzaro, E.; Comisso, L.; Valdettaro, L.

2010-01-01

In tokamaks magnetic islands arise from an unstable process of tearing and reconnecting of helical field lines across rational surfaces. After a linear stage the magnetic instability develops through three characteristic nonlinear stages where increasingly complex topological alterations occur in the form of the magnetic islands. The problem of response of reconnection process to the injection of an external current suitably localized is addressed using a four-field model in a plane slab plasma, with a novel extension to account consistently of the relevant neoclassical effects, such as bootstrap current and pressure anisotropy. The results found have implications on the interpretation of the possible mechanism of present day experimental results on neoclassical tearing modes as well as on the concepts for their control or avoidance.

Universities and Regional Development: A Critical Assessment of Tensions and Contradictions. International Studies in Higher Education

Science.gov (United States)

Pinheiro, Romulo, Ed.; Benneworth, Paul, Ed.; Jones, Glen A., Ed.

2012-01-01

Universities are under increasing pressure to help promote socio-economic growth in their local communities. However until now, no systematic, critical attention has been paid to the factors and mechanisms that currently make this process so daunting. In Universities and Regional Development, scholars from Europe, the Americas, Africa, and Asia…

Guide Actor-Critic for Continuous Control

OpenAIRE

Tangkaratt, Voot; Abdolmaleki, Abbas; Sugiyama, Masashi

2017-01-01

Actor-critic methods solve reinforcement learning problems by updating a parameterized policy known as an actor in a direction that increases an estimate of the expected return known as a critic. However, existing actor-critic methods only use values or gradients of the critic to update the policy parameter. In this paper, we propose a novel actor-critic method called the guide actor-critic (GAC). GAC firstly learns a guide actor that locally maximizes the critic and then it updates the polic...

Connectomes as constitutively epistemic objects: Critical perspectives on modeling in current neuroanatomy.

Science.gov (United States)

Haueis, Philipp; Slaby, Jan

2017-01-01

The term "connectome" is commonly taken to describe a complete map of neural connections in a nervous system of a given species. This chapter provides a critical perspective on the role of connectomes in neuroscientific practice and asks how the connectomic approach fits into a larger context in which network thinking permeates technology, infrastructure, social life, and the economy. In the first part of this chapter, we argue that, seen from the perspective of ongoing research, the notion of connectomes as "complete descriptions" is misguided. Our argument combines Rachel Ankeny's analysis of neuroanatomical wiring diagrams as "descriptive models" with Hans-Jörg Rheinberger's notion of "epistemic objects," i.e., targets of research that are still partially unknown. Combining these aspects we conclude that connectomes are constitutively epistemic objects: there just is no way to turn them into permanent and complete technical standards because the possibilities to map connection properties under different modeling assumptions are potentially inexhaustible. In the second part of the chapter, we use this understanding of connectomes as constitutively epistemic objects in order to critically assess the historical and political dimensions of current neuroscientific research. We argue that connectomics shows how the notion of the "brain as a network" has become the dominant metaphor of contemporary brain research. We further point out that this metaphor shares (potentially problematic) affinities to the form of contemporary "network societies." We close by pointing out how the relation between connectomes and networks in society could be used in a more fruitful manner. © 2017 Elsevier B.V. All rights reserved.

Hysteresis-controlled instability waves in a scale-free driven current sheet model

Directory of Open Access Journals (Sweden)

V. M. Uritsky

2005-01-01

Full Text Available Magnetospheric dynamics is a complex multiscale process whose statistical features can be successfully reproduced using high-dimensional numerical transport models exhibiting the phenomenon of self-organized criticality (SOC. Along this line of research, a 2-dimensional driven current sheet (DCS model has recently been developed that incorporates an idealized current-driven instability with a resistive MHD plasma system (Klimas et al., 2004a, b. The dynamics of the DCS model is dominated by the scale-free diffusive energy transport characterized by a set of broadband power-law distribution functions similar to those governing the evolution of multiscale precipitation regions of energetic particles in the nighttime sector of aurora (Uritsky et al., 2002b. The scale-free DCS behavior is supported by localized current-driven instabilities that can communicate in an avalanche fashion over arbitrarily long distances thus producing current sheet waves (CSW. In this paper, we derive the analytical expression for CSW speed as a function of plasma parameters controlling local anomalous resistivity dynamics. The obtained relation indicates that the CSW propagation requires sufficiently high initial current densities, and predicts a deceleration of CSWs moving from inner plasma sheet regions toward its northern and southern boundaries. We also show that the shape of time-averaged current density profile in the DCS model is in agreement with steady-state spatial configuration of critical avalanching models as described by the singular diffusion theory of the SOC. Over shorter time scales, SOC dynamics is associated with rather complex spatial patterns and, in particular, can produce bifurcated current sheets often seen in multi-satellite observations.

High critical currents in heavily doped (Gd,Y)Ba2Cu3Ox superconductor tapes

International Nuclear Information System (INIS)

Selvamanickam, V.; Gharahcheshmeh, M. Heydari; Xu, A.; Galstyan, E.; Delgado, L.; Cantoni, C.

2015-01-01

REBa 2 Cu 3 O x ((REBCO), RE = rare earth) superconductor tapes with moderate levels of dopants have been optimized for high critical current density in low magnetic fields at 77 K, but they do not exhibit exemplary performance in conditions of interest for practical applications, i.e., temperatures less than 50 K and fields of 2–30 T. Heavy doping of REBCO tapes has been avoided by researchers thus far due to deterioration in properties. Here, we report achievement of critical current densities (J c ) above 20 MA/cm 2 at 30 K, 3 T in heavily doped (25 mol. % Zr-added) (Gd,Y)Ba 2 Cu 3 O x superconductor tapes, which is more than three times higher than the J c typically obtained in moderately doped tapes. Pinning force levels above 1000 GN/m 3 have also been attained at 20 K. A composition map of lift factor in J c (ratio of J c at 30 K, 3 T to the J c at 77 K, 0 T) has been developed which reveals the optimum film composition to obtain lift factors above six, which is thrice the typical value. A highly c-axis aligned BaZrO 3 (BZO) nanocolumn defect density of nearly 7 × 10 11  cm −2 as well as 2–3 nm sized particles rich in Cu and Zr have been found in the high J c films

Regional estimation of geomagnetically induced currents based on the local magnetic or electric field

Directory of Open Access Journals (Sweden)

Viljanen Ari

2015-01-01

Full Text Available Previous studies have demonstrated a close relationship between the time derivative of the horizontal geomagnetic field vector (dH/dt and geomagnetically induced currents (GIC at a nearby location in a power grid. Similarly, a high correlation exists between GIC and the local horizontal geoelectric field (E, typically modelled from a measured magnetic field. Considering GIC forecasting, it is not feasible to assume that detailed prediction of time series will be possible. Instead, other measures summarising the activity level over a given period are preferable. In this paper, we consider the 30-min maximum of dH/dt or E as a local activity indicator (|dH/dt|30 or |E|30. Concerning GIC, we use the sum of currents through the neutral leads at substations and apply its 30-min maximum as a regional activity measure (GIC30. We show that |dH/dt|30 at a single point yields a proxy for GIC activity in a larger region. A practical consequence is that if |dH/dt|30 can be predicted at some point then it is also possible to assess the expected GIC level in the surrounding area. As is also demonstrated, |E|30 and GIC30 depend linearly on |dH/dt|30, so there is no saturation with increasing geomagnetic activity contrary to often used activity indices.

Current and Future Critical Issues in Rocket Propulsion Systems

Science.gov (United States)

Navaz, Homayun K.; Dix, Jeff C.

1998-01-01

The objective of this research was to tackle several problems that are currently of great importance to NASA. In a liquid rocket engine several complex processes take place that are not thoroughly understood. Droplet evaporation, turbulence, finite rate chemistry, instability, and injection/atomization phenomena are some of the critical issues being encountered in a liquid rocket engine environment. Pulse Detonation Engines (PDE) performance, combustion chamber instability analysis, 60K motor flowfield pattern from hydrocarbon fuel combustion, and 3D flowfield analysis for the Combined Cycle engine were of special interest to NASA. During the summer of 1997, we made an attempt to generate computational results for all of the above problems and shed some light on understanding some of the complex physical phenomena. For this purpose, the Liquid Thrust Chamber Performance (LTCP) code, mainly designed for liquid rocket engine applications, was utilized. The following test cases were considered: (1) Characterization of a detonation wave in a Pulse Detonation Tube; (2) 60K Motor wall temperature studies; (3) Propagation of a pressure pulse in a combustion chamber (under single and two-phase flow conditions); (4) Transonic region flowfield analysis affected by viscous effects; (5) Exploring the viscous differences between a smooth and a corrugated wall; and (6) 3D thrust chamber flowfield analysis of the Combined Cycle engine. It was shown that the LTCP-2D and LTCP-3D codes are capable of solving complex and stiff conservation equations for gaseous and droplet phases in a very robust and efficient manner. These codes can be run on a workstation and personal computers (PC's).

Mapping the Wolf-Hirschhorn syndrome phenotype outside the currently accepted WHS critical region and defining a new critical region, WHSCR-2.

Science.gov (United States)

Zollino, Marcella; Lecce, Rosetta; Fischetto, Rita; Murdolo, Marina; Faravelli, Francesca; Selicorni, Angelo; Buttè, Cinzia; Memo, Luigi; Capovilla, Giuseppe; Neri, Giovanni

2003-03-01

In an attempt to define the distinctive Wolf-Hirschhorn syndrome (WHS) phenotype, and to map its specific clinical manifestations, a total of eight patients carrying a 4p16.3 microdeletion were analyzed for their clinical phenotype and their respective genotypes. The extent of each individual deletion was established by fluorescence in situ hybridization, with a cosmid contig spanning the genomic region from MSX1 (distal half of 4p16.1) to the subtelomeric locus D4S3359. The deletions were 1.9-3.5 Mb, and all were terminal. All the patients presented with a mild phenotype, in which major malformations were usually absent. It is worth noting that head circumference was normal for height in two patients (those with the smallest deletions [1.9 and 2.2 Mb]). The currently accepted WHS critical region (WHSCR) was fully preserved in the patient with the 1.9-Mb deletion, in spite of a typical WHS phenotype. The deletion in this patient spanned the chromosome region from D4S3327 (190 b4 cosmid clone included) to the telomere. From a clinical point of view, the distinctive WHS phenotype is defined by the presence of typical facial appearance, mental retardation, growth delay, congenital hypotonia, and seizures. These signs represent the minimal diagnostic criteria for WHS. This basic phenotype maps distal to the currently accepted WHSCR. Here, we propose a new critical region for WHS, and we refer to this region as "WHSCR-2." It falls within a 300-600-kb interval in 4p16.3, between the loci D4S3327 and D4S98-D4S168. Among the candidate genes already described for WHS, LETM1 (leucine zipper/EF-hand-containing transmembrane) is likely to be pathogenetically involved in seizures. On the basis of genotype-phenotype correlation analysis, dividing the WHS phenotype into two distinct clinical entities, a "classical" and a "mild" form, is recommended for the purpose of proper genetic counseling.

Field, temperature, and angle dependent critical current density Jc(H,T, ) in coated conductors obtained via contact-free methods

Energy Technology Data Exchange (ETDEWEB)

Thompson, James R [ORNL; Sinclair IV, John W [ORNL; Christen, David K [ORNL; Zhang, Yifei [ORNL; Zuev, Yuri L [ORNL; Cantoni, Claudia [ORNL; Chen, Y [SuperPower Incorporated, Schenectady, New York; Selvamanickam, V. [SuperPower Incorporated, Schenectady, New York

2010-01-01

Applications of coated conductors based on high-Tc superconductors often require detailed knowledge of their critical current density Jc as a function of magnetic field orientation as well as field strength and temperature. This work demonstrates experimental methods to obtain the angularly dependent Jc using contact-free magnetic measurements, and qualifies those methods using several well defined conditions. The studies complement traditional transport techniques and are readily extended to conditions of field and temperature where the current density is very large and transport methods become difficult. Results on representative materials are presented.

Influence of microscopic inhomogeneity on macroscopic transport current of Ag/Bi2223 tapes

International Nuclear Information System (INIS)

Ogawa, Kazuhiro; Osamura, Kozo

2004-01-01

In Ag/Bi2223 tapes, inhomogeneities such as spatially distributed weak links or non-superconducting oxides are inevitably introduced because of the complicated manufacturing process and thermodynamic instability. In order to clarify the effect of the difference in such microscopic inhomogeneites on the macroscopic current transport properties, we carried out a numerical analysis. By changing volume fraction (V f ) of the Bi2223 phase and the shape of local distribution of critical current at each weak link, it is revealed that I-V characteristics are largely affected by the breadth of local distributions with different dependence on V f of Bi2223 and calculated results can be analyzed by Weibull distribution function with some parameters including the information of two-dimensional distribution

Relative importance of current and past landscape structure and local habitat conditions for plant species richness in dry grassland-like forest openings.

Science.gov (United States)

Husáková, Iveta; Münzbergová, Zuzana

2014-01-01

In fragmented landscapes, plant species richness may depend not only on local habitat conditions but also on landscape structure. In addition, both present and past landscape structure may be important for species richness. There are, however, only a few studies that have investigated the relative importance of all of these factors. The aim of this study was to examine the effect of current and past landscape structures and habitat conditions on species richness at dry grassland-like forest openings in a forested landscape and to assess their relative importance for species richness. We analyzed information on past and present landscape structures using aerial photographs from 1938, 1973, 1988, 2000 and 2007. We calculated the area of each locality and its isolation in the present and in the past and the continuity of localities in GIS. At each locality, we recorded all vascular plant species (296 species in 110 forest openings) and information on abiotic conditions of the localities. We found that the current species richness of the forest openings was significantly determined by local habitat conditions as well as by landscape structure in the present and in the past. The highest species richness was observed on larger and more heterogeneous localities with rocks and shallow soils, which were already large and well connected to other localities in 1938. The changes in the landscape structure in the past can thus have strong effects on current species richness. Future studies attempting to understand determinants of species diversity in fragmented landscapes should also include data on past landscape structure, as it may in fact be more important than the present structure.

Local buckling failure analysis of high-strength pipelines

Institute of Scientific and Technical Information of China (English)

Yan Li; Jian Shuai; Zhong-Li Jin; Ya-Tong Zhao; Kui Xu

2017-01-01

Pipelines in geological disaster regions typically suffer the risk of local buckling failure because of slender structure and complex load.This paper is meant to reveal the local buckling behavior of buried pipelines with a large diameter and high strength,which are under different conditions,including pure bending and bending combined with internal pressure.Finite element analysis was built according to previous data to study local buckling behavior of pressurized and unpressurized pipes under bending conditions and their differences in local buckling failure modes.In parametric analysis,a series of parameters,including pipe geometrical dimension,pipe material properties and internal pressure,were selected to study their influences on the critical bending moment,critical compressive stress and critical compressive strain of pipes.Especially the hardening exponent of pipe material was introduced to the parameter analysis by using the Ramberg-Osgood constitutive model.Results showed that geometrical dimensions,material and internal pressure can exert similar effects on the critical bending moment and critical compressive stress,which have different,even reverse effects on the critical compressive strain.Based on these analyses,more accurate design models of critical bending moment and critical compressive stress have been proposed for high-strength pipelines under bending conditions,which provide theoretical methods for highstrength pipeline engineering.

Nestling national ‘transformation’ imperatives in local ‘servicing’ space: critical reflections on an intergovernmental planning and implementation project

CSIR Research Space (South Africa)

Oranje, M

2011-12-01

Full Text Available (58) 8 CSIR, 2007a; CSIR, 2007b; CSIR, 2007c). In terms of the research for this article, the study was approached from an appreciative, yet critical perspective. Based mainly on ?Appreciative Inquiry?,2 which is rooted in social constructionist... from the national to the local level, with the aim of ensur- ing a very different economic and social outcome, through the pursuit of shared, sustainable, equitable and inclusive growth. At ?societal and individual level?, transformation also has...

The role of minimum supply and social vulnerability assessment for governing critical infrastructure failure: current gaps and future agenda

Directory of Open Access Journals (Sweden)

M. Garschagen

2018-04-01

Full Text Available Increased attention has lately been given to the resilience of critical infrastructure in the context of natural hazards and disasters. The major focus therein is on the sensitivity of critical infrastructure technologies and their management contingencies. However, strikingly little attention has been given to assessing and mitigating social vulnerabilities towards the failure of critical infrastructure and to the development, design and implementation of minimum supply standards in situations of major infrastructure failure. Addressing this gap and contributing to a more integrative perspective on critical infrastructure resilience is the objective of this paper. It asks which role social vulnerability assessments and minimum supply considerations can, should and do – or do not – play for the management and governance of critical infrastructure failure. In its first part, the paper provides a structured review on achievements and remaining gaps in the management of critical infrastructure and the understanding of social vulnerabilities towards disaster-related infrastructure failures. Special attention is given to the current state of minimum supply concepts with a regional focus on policies in Germany and the EU. In its second part, the paper then responds to the identified gaps by developing a heuristic model on the linkages of critical infrastructure management, social vulnerability and minimum supply. This framework helps to inform a vision of a future research agenda, which is presented in the paper's third part. Overall, the analysis suggests that the assessment of socially differentiated vulnerabilities towards critical infrastructure failure needs to be undertaken more stringently to inform the scientifically and politically difficult debate about minimum supply standards and the shared responsibilities for securing them.

The role of minimum supply and social vulnerability assessment for governing critical infrastructure failure: current gaps and future agenda

Science.gov (United States)

Garschagen, Matthias; Sandholz, Simone

2018-04-01

Increased attention has lately been given to the resilience of critical infrastructure in the context of natural hazards and disasters. The major focus therein is on the sensitivity of critical infrastructure technologies and their management contingencies. However, strikingly little attention has been given to assessing and mitigating social vulnerabilities towards the failure of critical infrastructure and to the development, design and implementation of minimum supply standards in situations of major infrastructure failure. Addressing this gap and contributing to a more integrative perspective on critical infrastructure resilience is the objective of this paper. It asks which role social vulnerability assessments and minimum supply considerations can, should and do - or do not - play for the management and governance of critical infrastructure failure. In its first part, the paper provides a structured review on achievements and remaining gaps in the management of critical infrastructure and the understanding of social vulnerabilities towards disaster-related infrastructure failures. Special attention is given to the current state of minimum supply concepts with a regional focus on policies in Germany and the EU. In its second part, the paper then responds to the identified gaps by developing a heuristic model on the linkages of critical infrastructure management, social vulnerability and minimum supply. This framework helps to inform a vision of a future research agenda, which is presented in the paper's third part. Overall, the analysis suggests that the assessment of socially differentiated vulnerabilities towards critical infrastructure failure needs to be undertaken more stringently to inform the scientifically and politically difficult debate about minimum supply standards and the shared responsibilities for securing them.