摘要:

AbstractFrom a study of the influence of the Ca: Pb ratio on the superconducting properties of Bibased ceramics of 2223 type it follows that as a second parameter the employed gas atmosphere must be taken into consideration. In case of air preparation good intragrain and intergrain properties are obtained for Ca rich samples (e.g. Bi1.8Pb0.2Sr1.9Ca2.1Cu3Oz); whereas for Pb rich materials (e.g. Bi1.7Pb0.5Sr1.9Ca1.9Cu3Oz) improved conditions are encountered by employment of an Ar/O2(8%) atmosphere during synthesis. Independently, the transition temperature is situated near 108 K.

ISSN:0003-3804    

DOI:10.1002/andp.19945060202

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractFlow‐equations are introduced in order to bring Hamiltonians closer to diagonalization. It is characteristic for these equations that matrix‐elements between degenerate or almost degenerate states do not decay or decay very slowly. In order to understand different types of physical systems in this framework it is probably necessary to classify various types of these degeneracies and to investigate the corresponding physical behavior.In general these equations generate many‐particle interactions. However, for ann‐orbital model the equations for the two‐particle interaction are closed in the limit of largen.Solutions of these equations for a one‐dimensional model are considered. There appear convergency problems, which are removed, if instead of diagonalization only a block‐diagonalization into blocks with the same number of quasiparticles

ISSN:0003-3804    

DOI:10.1002/andp.19945060203

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractIn the continuum approximation of the Su‐Schrieffer‐Heeger model for degenerate and nondegenerate ground state systems, an exhaustive survey of solutions of the standard gap equations is given. With special emphasis on the electronic energy spectrum, the pertinent results of Takahashi [1] are extended to the whole μ,k‐plane. Periodic metallic phases and their grand potentials are dis

ISSN:0003-3804    

DOI:10.1002/andp.19945060204

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

AbstractThe partial half‐lives of the hypothetical even‐even equivalent of an odd‐mass nucleus for cluster transitions toward various excited states of the daughter, used as a reference to find the hindrance factor, can be calculated within analytical superasymmetric fission model, by taking into account the angular momentum of the emitted cluster. Detailed tables are presented for14C radioactivity of221Fr,221,223Ra,225Ac;24Ne radioactivity of233U,231Pa, and23F decay of231Pa, showing that, except for225Ac, the existing experimental evidences, do not exclude (moderate) hindered transitions to the ground states of the daugther n

ISSN:0003-3804    

DOI:10.1002/andp.19945060205

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

摘要:

Acceleration of neutrons by isomeric nuclei.The inelastic neutron acceleration (INNA) by long living isomeric nuclei is studied. The theoretical estimates of the INNA cross‐sections for thermal neutrons for a number of isomers give the values in the range 0.1 ‐ 102b. Inelastic acceleration of thermal neutrons was observed by152mEu and180mHf, and confirmed the high value of the INNA cross‐sections. As a result of the high probability of acceleration some isomeric nuclei113mIn,115mIn, are not usual moderators but accelerators of neutrons. The use of the INNA reaction for the study of high excited levels and the nature of various nuclear hindrances are disc

ISSN:0003-3804    

DOI:10.1002/andp.19945060206

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY

ISSN:0003-3804    

DOI:10.1002/andp.19945060201

出版商:WILEY‐VCH Verlag    

年代:1994

数据来源: WILEY