共查询到20条相似文献,搜索用时 12 毫秒
1.
B. Zhang P. Fabbricatore G. Gemme R. Musenich R. Parodi P. Capobianco 《Journal of Superconductivity》1995,8(6):753-757
In the present work a cavity fully coated with an YBCO thick film was fabricated using an improved electrophoretic deposition technology with a special attempt to avoid the possible contamination of the superconducting powder during the milling process in the suspension preparation. A microwave experimental set-up was constructed to measure the rf behavior of the cavity in a wide temperature range. The loaded quality factorQ
1 and the shift of the resonant frequency vs. the temperature at various rf magnetic fields have been measured. Furthermore, the surface resistance and the penetration depth determined from the measurements were compared with the numerical calculation in the framework of BCS theory, showing good agreement with the theoretical predictions. 相似文献
2.
A theoretical discussion is presented on the energy loss in a multi-filamentary superconducting wire when an applied transport current and an external transverse magnetic field are varied simultaneously with a repeating pulsive wave form. In the present calculation, the effects of the ‘uniforming time constant’ which has been introduced by the authors as a characteristic time constant for the change in the transport-current distribution inside the wire is taken into account, together with the field dependence of the critical current density of superconducting filaments.Thus the present analytic expression for the energy loss of multi-filamentary wire is available to the whole range of the external magnetic field. It is shown that the contribution of the dynamic resistance loss to the total loss is strongly dependent on the position of the wire inside a coil. 相似文献
3.
Heat transfer measurements have been carried out on the liquid He4 in a side arm rotating at a speed of 3000 rpm. The heat transfer cell consists of a copper disc mounted perpendicularly to the radial direction at a radial distance of 0.41 m. A correlation of the type: where S is the stratification factor, has been obtained.The flow pattern of He4-gas through a U-tube under a self-pumping system in a rotating frame has been studied analytically. It can be demonstrated that the flow polarity is influenced by the velocity gradient of the friction factor in the region, between stream-line and turbulent motions, which can lead to flow instability of the kind observed experimentally recently. It has been explained that the instability may occur in both increasing and decreasing speed modes or heat inputs. 相似文献
4.
Cheng Zeng Zhengxiang Luo Qishao Zhang Kai Yang 《Journal of Superconductivity and Novel Magnetism》2009,22(4):319-323
A multimode sapphire resonator is developed for multiple frequency surface resistance measurement of a single piece of high-temperature
superconductor thin film. Simple formulas are used for the calculations of surface resistances. On this sapphire resonator,
three modes, TE011+ε
, TE012+δ
and TE021+ξ (0<ε,δ,ξ<1), which had resonances at 11.84, 17.49 and 31.99 GHz were used simultaneously and the measured surface resistances at
these frequencies were 0.553, 1.32 and 3.75 mΩ, respectively. The measured result matches the theory very well. 相似文献
5.
Errors in measurements of surface resistanceR
s
of HTS materials are due to discrepancy between a mathematical model describing physical phenomena and a real measurement environment, finite accuracy of measurements of theQ-factor, and finite accuracy of constants used for calculation ofR
s
. In this paper we analyze errors inR
s
due to uncertainties in theQ-factor, geometrical coefficients, loss tangent,R
scu, and other factors when a cylindrical copper cavity with an HTS end plate, a stripline resonator, and sapphire rod resonators are used for HTS characterization. 相似文献
6.
E. L. Wolf A. Chang Z. Y. Rong Yu. M. Ivanchenko Farun Lu 《Journal of Superconductivity》1994,7(2):355-360
Scanning tunneling spectroscopy applied to BiO cleavage planes of 90 KT
c BSCCO 2212 at 4.2 K simultaneously provides topography and localdI/dV spectra (superconducting DOS). The spectra, which are similar to recent photoemission spectra, confirm a large gap parameter (x, y) associated with an apparently gapless DOS on the uppermost layer. Transverse spatial variations of on a 100 Å scale are attributed to variations in BiO metallicity, presumably originating in oxygen stoichiometry variations in an unannealed crystal. We identify two characteristicdI/dV spectral shapes with regions of metallic and nonmetallic BiO layers, and can relate these by the McMillan model of the superconducting proximity effect. A sharply peaked spectral shape, similar to that observed in photoemission, is predicted for the metallic BiO layer induced superconducting by its proximity to the underlying CuO2 planes. The short mean free path and short coherence length imply that both tunneling and photoemission spectra are heavily weighted toward contributions from the BiO layer in fully metallic 2212. The present results and analysis thus suggest that the superconducting proximity effect influences the lineshapes seen by both techniques. 相似文献
7.
T. Tominaka H. Ikeda A. Yamamoto K. Tsuchiya M. Takasaki T. Shintomi H. Hirabayashi Y. Narahara 《低温学》1982,22(4):161-166
The beam induced quench of a superconducting solenoid was studied to estimate the effect of the energy deposition due to the high energy proton beam. The solenoid was directly exposed to 12 GeV proton beam with a typical beam duration time of 250 ms. The experimental results were compared with the MPZ/Cold-End energy calculation and a computer simulation solving the thermal equation. They can be well reproduced by the simulation result with reasonable parameters. 相似文献
8.
水镁石粉体是聚合物的常用填料,但水镁石极性较大,与基材的相容性也较差,因此必须通过表面改性,降低水镁石粉体表面能,增强亲油疏水性,从而增加与聚合物之间的相容性,而阴离子表面活性剂是合适的改性剂之一。水镁石粉体改性后的表面性能,可以用固体表面能数值的变化来表征,本文选择丙三醇、水、1-溴代萘为探针液体,用直接测定法与Washburn方程间接计算法获得了改性前后水镁石的接触角,通过Lifshitz-van der Waals acid base三参数法计算其表面能。研究结果表明,不同的阴离子基团中,羧酸类、磷酸较之磺酸类硫酸类改性效果有明显优势,表面能的碱分量γ-S和酸分量γ+S降为0;随着改性剂中非极性链烃的碳原子个数增加,表面能非极性分量γLSW下降很多,最终导致总表面能下降,接触角增加,疏水性增强。 相似文献
9.
We study the surface gap solitons in an interface between one-dimensional dual-frequency lattices and uniform media. We reveal that the property of these lattices features solitons with some unique properties. It is worth pointing out that the intensity peak position of a soliton moves away from the surface of the lattice as the soliton's power for large propagation constant increases, and at the critical value of propagation constant μ = 2.1 (corresponding to power P = 6.1), the soliton closest to the surface of the lattice is formed, which reveals that low power is enough to form a real surface dual-frequency lattice soliton. These properties are contrary to those of surface solitons formed with the aid of semi-infinite symmetrical lattices. 相似文献
10.
Surface Energy and Surface Stability of Ag Nanocrystals at Elevated Temperatures and Their Dominance in Sublimation‐Induced Shape Evolution
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Long‐Bing He Lei Zhang Xiao‐Dong Tan Lu‐Ping Tang Tao Xu Yi‐Long Zhou Zhan‐Yong Ren Yun Wang Chun‐Yu Teng Li‐Tao Sun Jian‐Feng Nie 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(27)
The surface energy and surface stability of Ag nanocrystals (NCs) are under debate because the measurable values of the surface energy are very inconsistent, and the indices of the observed thermally stable surfaces are apparently in conflict. To clarify this issue, a transmission electron microscope is used to investigate these problems in situ with elaborately designed carbon‐shell‐capsulated Ag NCs. It is demonstrated that the {111} surfaces are still thermally stable at elevated temperatures, and the victory of the formation of {110} surfaces over {111} surfaces on the Ag NCs during sublimation is due to the special crystal geometry. It is found that the Ag NCs behave as quasiliquids during sublimation, and the cubic NCs represent a featured shape evolution, which is codetermined by both the wetting equilibrium at the Ag–C interface and the relaxation of the system surface energy. Small Ag NCs (≈10 nm) no longer maintain the wetting equilibrium observed in larger Ag NCs, and the crystal orientations of ultrafine Ag NCs (≈6 nm) can rotate to achieve further shape relaxation. Using sublimation kinetics, the mean surface energy of Ag NCs at 1073 K is calculated to be 1.1–1.3 J m?2. 相似文献
11.
The mechanism of frictional motion and its effects at 4.2 K in superconducting magnet winding models
Frictional sliding occurs on both a microscopic and a macroscopic scale. Sliding on a microscopic scale appears as discrete events called microslips. Microslips are inherent in all sliding events and are quite different from macroscopic instabilities such as stick-slips. It is thought that the training effect observed in quench current data from a superconducting braid may be caused by microslips.The mechanisms of sliding motion and its effects at 4.2 K were studied in detail for a number of metal/insulator pairs that model superconducting magnet windings; the results impact the performance of superconducting magnets. Organic surface coating materials are generally effective in eliminating macroscopic instabilities. Instrumentation used in these experiments includes a high-resolution extensometer and an acoustic emission sensor, both with sensitivities capable of detecting microslips (~ 1 μm). 相似文献
12.
D. Wolfshtein T. E. Seidel D. W. Johnson Jr. W. W. Rhodes 《Journal of Superconductivity》1989,2(2):211-218
A device for the frictionless transport of light payloads, e.g., silicon wafers, using superconducting magnetic levitation has been demonstrated. The device consists of an array of rigidly connected carrier magnets levitating above a corresponding array of superconducting discs. Silicon wafers placed on the carrier have been linearly transported with velocities up to 50 cm/s. The configuration provides for excellent lateral stability. Studies of the height and lateral friction effects (caused by flux pinning) were measured as a function of payload mass. Future applications may include the frictionless transport of silicon wafers in vacuum environments. 相似文献
13.
A.P. Bramley A.J. Wilkinson A.P Jenkins C.R.M. Grovenor 《Journal of Superconductivity》1998,11(1):71-72
Tl2Ba2Ca2Cu3Ox thin films have been fabricated on (001) LaAlO3 and (001) MgO substrates. Films grown on LaAlO3 have Tc=112K and RS(80K, 10GHz)=0.2m, while films on MgO have Tc=117K and Rs(80K, 10GHz)=0.7m. The grain size and alignment of the films has been investigated using X-ray diffraction, Scanning Electron Microscopy and Electron Backscattered Diffraction. We show evidence for a markedly higher in-plane angular spread for films on MgO and believe that for films grown on this substrate the lowest achievable values of Rs are limited by disorder in the in-plane alignment of the TBCCO film caused by the large lattice mismatch between the materials. 相似文献
14.
The Argonne National Laboratory has designed, constructed and tested a large aperture superconducting MHD magnet for use in the coal-fired flow facility at Tullahoma, Tennessee. The magnet generates a peak on-axis field of 6 T in a MHD warm bore of 80 cm diameter at inlet, 100 cm diameter at outlet, and 300 cm effective length. The stored energy of the magnet is 210 MJ, the cold mass (4.2 K) is 131 metric tons and the ampere-turns, 13.7 × 106. The final design of the magnet will be briefly introduced. Described in detail are the experiences of coil winding and coil assembly, the assembly of force-containment superstructure, assembly of magnet cryostat and results of magnet performance tests. 相似文献
15.
P. Chowdhuri 《低温学》1982,22(4):171-180
A dc superconducting cable is ideal for transmitting large blocks of electrical power over a long distance. However, it must be designed to operate reliably within the constraints of the electrical system. Therefore, system analysis must be performed for each application. The conductor losses caused by the harmonics on the dc must be within the design goals; a system fault should not drive the cable normal with eventual damage to the cable and interruption of power flow; and, the dielectric system of the cable must be designed to be compatible with the expected transient voltages by proper insulation coordination. Transient overvoltages are of concern to electrical power systems; these are especially critical to cryogenic cables because of the susceptibility of the cryogenic enclosures to these transients. This paper discusses the electrical system constraints which are particularly applicable to a dc superconducting cable and shows how such a cable can be designed to be compatible with the electrical system.This paper also summarizes the work on low temperature dielectrics performed at Los Alamos. It shows the variation of break down voltage of dielectric materials, in sheet form and cable configuration, with temperature and pressure under dc and impulse voltage. The surface flashover characteristics with large creepage distance as well as electrical conductivity of dielectric materials at cryogenic temperatures are discussed. These studies are essential for the design of high voltage apparatus operating in cryogenic environments. 相似文献
16.
AC losses of various kinds of pulsed conductors were measured. First we found that the ac losses of braid filled with Pb-Sn solder were much greater than those of the braid without filler. Since the braid consists of ‘three component strands’ with the mixed matrix of Cu and CuNi, the intra-strand coupling loss should be quite small. Therefore, we concluded that the large increase in ac losses due to solder-filling was caused by the inter-strand coupling through the outer copper sheath. To verify this, we measured the ac losses of two kinds of braids composed of Cu- and CuNi-sheathed strands, respectively. Both samples had the same size and characteristics except that one had copper sheath, while the other had cupro-nickel one. By replacing Cu sheath with CuNi, the ac losses were decreased to the level of those of the braid with Cu- sheathed strands.We also measured the ac losses of the compacted cables, one, filled with Ag-Sn solder and two, without solder. Again, solder filling caused an increase in the ac losses.When cables are not solder-filled, contact resistance among strands cuts the inter-strand coupling effectively. 相似文献
17.
The Bi-Pb-Sr-Ca-Cu-O superconductor was prepared by the three-step reaction process; the effects of Sr/Ca ratio and CuO content on the formation of the superconducting phases were studied. The Sr-short and Cu-rich nominal compositions are not advantageous for the formation of the 2223 phase but we are favored for the formation of the 2201 phase. The differences among the previous reports on the effect of composition on the formation of the superconducting phase is discussed. The best J
c
value of the Ag-sheathed tape filled with the kind of powder is 13,000 A/cm2 (77 K, OT). 相似文献
18.
Multifilamentary superconducting conductors, which are usually manufactured by hot extrusion and cold drawing, consist of bundles of small diameter superconducting filaments embedded in a normal conducting matrix. It is most desirable for the magnet designer as well as for the conductor manufacturer to control the uniformity of properties along the length of conductors which will be used in large magnets. In this paper we present a continuous monitoring of the superconducting and normal matrix areas through a non-destructive sampling procedure over the whole length of a superconducting conductor. 相似文献
19.
The application of joints which can be disassembled is studied within the framework of the development of high current (25 kA), high power (0.5 kW) cryogenic current supplies (flux pumps).1,2 The behaviour of a scale model with currents up to 5 kA will be presented here.Several means of diminishing the joint resistance have been researched with special attention being paid to detection methods to measure the resistance, and their accuracies.The role of the solder has been investigated. A simple model gives good qualitative understanding of the matter.The presence of ac currents in a cryogenic current supply causes considerably higher losses in the joint because of the non-homogeneous distribution of the current. A good impression of this distribution can be obtained by measuring the field along the joint. The measured results are in good agreement with calculated ones. A useful length of the joint under ac conditions can be defined and is helpful for design purposes. 相似文献
20.
Nasreen Hussein 《International Journal of Pavement Engineering》2017,18(11):1016-1026
The study reported herein focuses on assessing the effects and contributions of pavement surface condition parameters including roughness, rut depth and skid resistance on crash frequencies and rates at signalised intersections. The assessment has been performed using graphical trend analysis and negative binomial regression. For each signalised intersection in the sample, condition data are collected for the year before and after the year of surface treatment. Crash data, however, are collected for a minimum of 3 and maximum of 5 years before and after treatment years. Analyses results show that before treatment, light condition (day/night), road surface moisture condition (wet/dry) and skid resistance are the significant contributors to crash occurrence. For after-treatment; light condition, road surface moisture condition and the interaction between roughness and traffic volume are the significant contributors. The study aim and approach are presented herein together with a discussion of the main findings. 相似文献