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Biagi, K.R.
Iowa State Univ. of Science and Technology, Ames (USA)1985
Iowa State Univ. of Science and Technology, Ames (USA)1985
AbstractAbstract
[en] This thesis is divided into two sections, each dealing with the response of a superconducting proximity system to an applied magnetic field. In Section I, the maximum supercurrent that can be carried in an applied perpendicular magnetic field by a superconducting normal-metal superconducting (SNS) junction consisting of a square normal-metal layer sandwiched between two crossed perpendicular superconducting strips is investigated theoretically. For weak applied fields, the critical current is suppressed reversibly as induced Meissner screening currents flow into the SNS sandwich and generate a spatially varying magnetic field largely parallel to the junction, thereby altering the local phase difference. For stronger applied fields, the critical current is changed irreversibly as vortices enter and become pinned in the junction. In Section II, Eilenberger's quasi-classical formulation of superconductivity is used to derive an equation for the upper critical field of a multilayered SN system in a perpendicular magnetic field. The alternating layers are coupled via the proximity effect and are in the dirty limit
Primary Subject
Secondary Subject
Source
1985; 102 p; University Microfilms Order No. 85-24,634; Thesis (Ph. D.).
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Report
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Thesis/Dissertation
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INIS IssueINIS Issue
AbstractAbstract
[en] Ni-Ti superconducting wires with multifilamentar configuration were produced, using the grouping technique. Some basic concepts on superconductivity and its main critical parameters are presented. The criteria for stabilizing superconductors in terms of the geometry are studied. The main critical parameters, Hc, Jc, Tc in function of the composition and the metallurgical structure of Ni-Ti alloy are analysed. The development of Ni-Ti superconducting wires is described. (M.C.K.)
[pt]
Fios supercondutores de Ni-Ti com configuracao multifilamentar foram produzidos usando-se a tecnica de agrupamento. Apresentam-se alguns conceitos basicos sobre supercondutividade e seus principais parametros criticos. Estudam-se os criterios para a estabilizacao de supercondutores em termos de geometria. Analisam-se os principais parametros criticos, Hc, Jc, Tc em funcoes da composicao e da estrutura metalurgica da liga Ni-Ti. Descreve-se o desenvolvimento dos fios supercondutores de Ni-Ti. (M.C.K.)Original Title
Desenvolvimento de fios supercondutores multifilamentares de Nb-Ti
Primary Subject
Source
1986; 121 p; Tese (M.Sc.).
Record Type
Miscellaneous
Literature Type
Thesis/Dissertation
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Country of publication
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Lee, Chang-Young.
State Univ. of New York, Buffalo, NY (United States)1993
State Univ. of New York, Buffalo, NY (United States)1993
AbstractAbstract
[en] In this thesis, the authors studied physical properties of various high-Tc superconductors by means of the ac susceptibility technique. They present the physics of ac susceptibility from first principles without relying on any specific models. From this, they can explain some fundamental but interesting features of experimental results such as symmetry properties of the ac susceptibility and its harmonics with respect to dc magnetic field. By measuring ac hysteresis they were able to obtain lower critical fields which were compared with some theoretical predictions. They found that the results were consistent with the BCS theory with modified gap parameter. By measuring ac hysteresis of granular samples at ultra low magnetic fields, they revealed the Meissner state and obtained Josephson lower critical fields, which was also found to be in consistence with the BCS theory. They studied the critical state models in detail and obtained some useful equations which were used in analyzing magnetic field dependence of ac susceptibility. By comparing the equations with experimental results, they were able to perform quantitative analysis of some important physical parameters such as critical current density. From numerical calculations of ac susceptibility with the parameter values obtained by this procedure, they confirmed good agreement of theory with experimental data. They incorporated the theory of flux creep into the equation governing the steady state flux motion, from which they were able to explain the shift of ac susceptibility with operating frequency toward high temperatures. Through this study, quantitative results on the activation energy were obtained
Secondary Subject
Source
1993; 186 p; State Univ. of New York; Buffalo, NY (United States); Available from University Microfilms, P.O. Box 1764, Ann Arbor, MI 48106 (United States). Order No. 93-01,872; Thesis (Ph.D.).
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Miscellaneous
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Spiegelberg, R. de S.H.
Instituto Militar de Engenharia, Rio de Janeiro (Brazil)1981
Instituto Militar de Engenharia, Rio de Janeiro (Brazil)1981
AbstractAbstract
[en] Critical parameters were calculated using the one-dimensional multigroup transport theory. Calculations have been performed for water mixture of uranium metal and uranium oxides and plutonium nitrates to determine the dimensions of simple critical geometries (sphere and cylinder). The results of the calculations were plotted showing critical parameters (volume, radius or critical mass). The critical values obtained in Handbuch zur Kritikalitat were used to compare with critical parameters. A sensitivity study for the influences of mesh space size, multigroup structure and order of the S sub(n) approximation on the critical radius was carried out. The GAMTEC-II code was used to generate multigroup cross sections data. Critical radius were calculated using the one-dimensional multigroup transport code DTF-IV. (Author)
[pt]
Realizou-se o estudo de parametros criticos utilizando a teoria do transporte de neutrons, a uma dimensao, em misturas homogeneas aquosas de uranio metalico, oxido de uranio e nitrato de plutonio, em geometria esferica e cilindrica. A variacao da massa critica, do volume critico ou do diametro critico da solucao sao determinados e comparados com dados obtidos no Handbuch zur Kritikalitat. A sensibilidade do tamanho da malha espacial, da estrutura de multigrupo de energia e da ordem da aproximacao S sub(n) para o tratamento da equacao do transporte de neutrons, com o raio critico e estudada em cada caso. Foram utilizados para os calculos de criticalidade os programas GAMTEC-II11, para o calculo das secoes de choque multigrupo, e DTF-IV15 para o calculo espacial e determinacao do raio critico. Ambos os programas foram implantados nos sistemas computacionais da PUC-Rio e da CNEN. (Autor)Original Title
Calculos de criticalidade em misturas homogeneas de uranio e plutonio
Primary Subject
Source
May 1981; 127 p; Tese (M.Sc.).
Record Type
Miscellaneous
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Brand, R.A.
Cornell Univ., Ithaca, N.Y. (USA)1972
Cornell Univ., Ithaca, N.Y. (USA)1972
AbstractAbstract
No abstract available
Original Title
Nb-Ti and Ti-V
Primary Subject
Source
1972; 168 p; University Microfilms Order No. 73-9340.; Thesis (Ph. d.).
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Report
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Wallace, B.A. Jr.
Duke Univ., Durham, N.C. (USA)1971
Duke Univ., Durham, N.C. (USA)1971
AbstractAbstract
No abstract available
Primary Subject
Source
1971; 161 p; University Microfilms Order No. 72-8500.; Thesis. (Ph.D.).
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Report
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AbstractAbstract
[en] 36 different NbTi superconductor wires with 42, 49 and 54 weight % Ti and different thermo-mechanical treatments have been investigated. Critical currents up to the critical magnetic field Bsub(c2) have been measured, the maximum pinning force Pv max derived and the curves Bmax=B(Pv max) drawn. With 49 and 54 % Ti there is additional pinning by precipitates. For high fields, >8T the positive effect of higher pinning forces is outweighted by lower critical fields Bsub(c2) and the critical currents are smaller than at 42 %. In the region B >= 0, 8 Bsub(c2) there is good agreement with R Schmecker's (1977) model of plastic deformation of the flux line lattice. The line pinning hypothesis was also confirmed for this material and this field range. (G.Q.)
Original Title
Kritische Stroeme in NbTi-Supraleitern bis Hsub(c2)
Primary Subject
Source
1983; 65 p; Available from Technical University Vienna, Karlsplatz 13, A-1040 Vienna; Ref. no. 174115 II.; Diplomarbeit (Dipl. Ing.).
Record Type
Miscellaneous
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Ruel, R.R.
Rutgers--the State Univ., New Brunswick, NJ (USA)1985
Rutgers--the State Univ., New Brunswick, NJ (USA)1985
AbstractAbstract
[en] Liquid 3He under zero external magnetic field undergoes a second-order transition to a superfluid state at a pressure dependent temperature, T/sub c/, of about 2 mK. When a magnetic field is applied to liquid 3he, the transition splits into two second-order transitions occurring at T/sub c1/ (>T/sub c/) and T/sub c2/ (< T/sub c/). These two transition temperatures, separated by approximately 5 μK per kilogauss applied field, delineate the A1 phase. The superfluid component of the A1 phase is made up of pairs of 3He atoms whose nuclear magnetic moments are directed parallel to the external magnetic field. The second order transition at T/sub c1/ is a transition in which relative spin-gauge symmetry is broken. This unique broken symmetry results in the appearance of a hydrodynamic mode involving transport of mass, entropy, and spin angular momentum. One of the consequences of the existence of this mode is that superfluid flow can be generated by applying a magnetic field gradient across a superleak connecting two vessels of 3He-A1. This is called the magnetic fountain effect. The magnetic fountain effect was used to determine the orientation of the magnetic moments in the external field. Measurements were made of the width (in temperature) of the A1 phase at two pressures. Critical flow was driven magnetically and the critical velocity was measured through the A1 phase at two pressures. Critical flow was driven magnetically and the critical velocity was measured through the A1 phase to within 0.5 μK of T/sub c1/
Source
1985; 174 p; University Microfilms Order No. 85-02,403; Thesis (Ph. D.).
Record Type
Report
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Johnson, P.E.
Lawrence Berkeley Lab., CA (USA)1987
Lawrence Berkeley Lab., CA (USA)1987
AbstractAbstract
[en] In high magnetic fields, the critical current density is strongly dependent on the upper critical field, which is determined primarily by the stoichiometry of the Nb3Al. The critical temperature (T/sub c/), like the upper critical field, is considered to be a measure of the ''intrinsic'' quality of the superconductor, indicating the stoichiometry, order, and strain. If the A15 phase is stoichiometric and well ordered, a high T/sub c/ (and high H/sub C2/) is expected, regardless of the volume fraction of superconductor. On the other hand, if sigma phase is present with the A15, the resultant composition gradient across the sigma-A15 interface(s) requires that some of the A15 be off-stoichiometric, and therefore that the T/sub c/ (and H/sub C2/) be low. Thus the extent of the A15 (Nb3Al) reaction and the quality of the A15 formed are interdependent. This work focuses on the factors that control the extent of Nb3Al formation in Nb/Al powder wires. The morphology and content of the reacted and unreacted wires are studied in optical, SEM, and TEM micrographs. Critical current density data and its dependence on processing are explained in terms of the unreacted microstructure and its effect on the extent of Nb3Al formation. As a method of improving the critical current density, a new variation of the conventional powder process for wire manufacturing is developed and tested
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May 1987; 51 p; Available from NTIS, PC A04/MF A01; 1 as DE87012889; Portions of this document are illegible in microfiche products.; Thesis.
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Report
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AbstractAbstract
[en] In this thesis, the magnetic characterization of some Bi1.6Pb0.4Sr2Ca2Cu3O10, Bi1.84Pb0.34Sr1.91Ca2.03Cu2.06O10, Tl2Ba2Ca2Cu3O10 and Bi-2212/Ag high temperature superconductors were given by ac magnetic susceptibility and electrical resistivity measuring techniques. Bi1.6Pb0.4Sr2Ca2Cu3O10 and Bi1.84Pb0.34Sr1.91Ca2.03Cu2.06O10 high temperature superconductors were prepared by liquid ammonium nitrate method, while conventional solid state reaction route was applied to make Tl2Ba2Ca2Cu3O10 superconductor. On the other hand, Powder-In Tube (PIT) technique was used to make multi-filamentary Bi-2212/Ag tapes. Structural characterizations were carried out by X-ray powder diffraction (XRD) patterns and scanning electron microscopy (SEM). Unit cell parameters of Bi1.6Pb0.4Sr2Ca2Cu3O10 and Tl2Ba2Ca2Cu3O10 high temperature superconductors which have tetragonal crystal structure were calculated as a=b=5.3538 AA and c=37.1137 AA, a=b=3.8520 AA and c=35.5970 AA respectively. The results are consistent with the literature. Some information with regards to the grain size and phase content were given by the SEM studies. Fundamental and high order ac susceptibilities, χ=χn'''+iχn''(n=1, 2, 3, 5 and 7) of the samples were measured for the temperature range 15 K-140 K, ac field range 8 A/rn-1600 A/m and the frequency range 11 Hz-2110 Hz. All the susceptibilities exhibit field, frequency and temperature dependences. The observed dependences were analyzed using Bean model. For temperature scaling a function of the form Hp=Hα(l-t)''β was found empirically. The best fitting parameters for the Bi1.6Pb0.4Sr2Ca2Cu3O10 superconductor were found as Hα 3.3x104 A/m and β=2.05. Odd-order harmonic susceptibilities were calculated from the Bean model to make comparison with the experiments. In addition, ac losses were also calculated from the Bean model to compare with the experimentally measured values. At low temperatures and fields, the Bean model is observed to account for the ac losses. However, some deviations from the model were seen for high temperature and high field values. Finally, the ac field was applied to parallel (PAR) and perpendicular (PER) to the multi-filamentary tapes of Bi-2212/Ag. The fundamental harmonic susceptibilities exhibit field and frequency dependences. The results were dependent on the orientation of the specimen which was placed parallel or perpendicular to the applied field
Original Title
Yueksek sicaklik sueper iletkenlerde fiziksel oezellikler
Secondary Subject
Source
Oct 2003; 127 p; Also available from Turkish Atomic Energy Authority; Thesis (Ph. D.)
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