ISSN:1044-8632    

DOI:10.1080/10448639708231965

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639708231966

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639708231967

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639708231968

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639708231969

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:1044-8632    

DOI:10.1080/10448639708231970

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Recently, we have set up a neutron polarization analysis spectrometer (PAS) at the Dhruva reactor, Trombay for magnetic scattering studies [1,2], This polarized neutron spectrometer can be used in different modes, such as diffraction mode (2-aisc onfiguration), polarization analysis mode (3-axis configuration in scattering geometry), and depolarization mode (3-axis configuration in transmission geometry). We describe here some of the salient features of the construction and principles of this polarized neutron spectrometer. The feasibility of carrying out polarization analysis and depolarization studies using this spectrometer are also discussed.

ISSN:1044-8632    

DOI:10.1080/10448639708231971

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The main chains are liquid crystalline polymers (LCP) [I], obtained from an alternative succession of liquid crystal segments (mesogens) and spacers (generally alkyl groups) (Figure 1). These polymers are of a great technical interest since they may have both the elastic properties of polymers and the liquid crystalline proper-ties of the mesogenic segments. The bulk of such polymers present the characteristic phases of liquid crystals as a function of the temperature: isotropic, nematic, or sometimes smectic. They exhibit very low solubilities in common organic solvents and very high nematicisotropic transition temperatures (22OOOC). These reasons have been major obstacles for the investigation of the chain conformation by the classical methods generally used to study polymers, and explain why such studies are rare. In the nematic phase, the mesogens are aligned along the nematic direction. The competition between the long-range nematic order and the tendency of the polymer to maximize its entropy by having the conformation of a gaussian coil leads to two models [2] (Figure 1). In the first one, the chain undulates around the nematic director. In the other one, the conformation presents hairpin defects where the chain executes abrupt reversals. Their existence can have an important role in the rheology, in the non linear dielectric and optical properties of main chain LCPs. Thus, the problem arising from this new class of polymers was the determination of the polymer chain conformation in the isotropic and nematic phases.

ISSN:1044-8632    

DOI:10.1080/10448639708231972

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Heavy Fermions form an exotic branch of magnetism and have been studied extensively during the last two decades. The term heavy Fermions refers to highly correlated electron systems and is usually applied to rare earth and actinide metals, their alloys and intermetallic compounds which exhibit, among other interesting phenomena, two main characteristic properties: 1) enhanced Pauli paramagnetic susceptibility, i.e. constant c(o) as T → 0 K, and 2) enhanced linearly temperature dependent low temperature specific heat. These properties represent Fermi-liquid behavior, and in a free electron model for a metal, they are related to the conduction electron density of states at the Fermi level. The strongly enhanced coefficient yof the linear term in the specific heat interpreted this way suggests “quasiparticles” with very heavy “effective” mass at the Fermi level (up to – 2–3 orders of magnitude larger than the free electron mass). Observations of superconductivity in for example CeCu,Si, accompanied by a specific heat “jump” (the h-anomaly) consistent with heavy mass superconducting “carriers” [1] as well as the clear evidence for heavy “quasi-particles” on the Fermi surface from de Haas van Alphen measurements on CeSn, [2] represent two of the many remarkable manifestations of the heavy Fermion state.

ISSN:1044-8632    

DOI:10.1080/10448639708231973

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A great many different experiments have been carried out to try to understand the electronic interactions in high-Tcsuperconductors. No one technique has been able to give us a complete picture, and several rather important problems stubbornly refuse to yield despite having received an intensive battering from all sides. What, for example, is the symmetry of the paired state? And, which aspects of the electronic structure are central to the establishment of bulk superconductivity at elevated temperatures?

ISSN:1044-8632    

DOI:10.1080/10448639708231974

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor