Structural and Magnetic Properties of Pyrochlore Solid Solutions (Y,Lu)2Ti2-x(Nb,Ta)xO7+/-y

The synthesis and characterization of the pyrochlore solid solutions, Y2Ti2-xNbxO7-y, Lu2Ti2-xNbxO7-y, Y2Ti2-xTaxO7-y and Lu2TiTaO7-y (-0.4<y<0.5), is described. Synthesis at 1600 C, and 10-5 Torr yields oxygen deficiency in all systems. All compounds are found to be paramagnetic and semiconducting, with the size of the local moments being less, in some cases substantially less, than the expected value for the number of nominally unpaired electrons present. Thermogravimetric analysis (TGA) shows that all compounds can be fully oxidized while retaining the pyrochlore structure, yielding oxygen rich pyrochlores as white powders. Powder neutron diffraction of Y2TiNbO7-based samples was done. Refinement of the data for oxygen deficient Y2TiNbO6.76 indicates the presence of a distribution of oxygen over the 8b and 48f sites. Refinement of the data for oxygen rich Y2TiNbO7.5 shows these sites to be completely filled, with an additional half filling of the 8a site. The magnetic and TGA data strongly suggest a preference for a Ti3+/(Nb,Ta)5+ combination, as opposed to Ti4+/(Nb,Ta)4+, in this pyrochlore family. In addition, the evidence clearly points to Ti3+ as the source of the localized moments, with no evidence for localized Nb4+ moments.Comment: Accepted to Journal of Solid State Chemistr

Structural Disorder, Octahedral Coordination, and 2-Dimensional Ferromagnetism in Anhydrous Alums

The crystal structures of the triangular lattice, layered anhydrous alums KCr(SO4)2, RbCr(SO4)2 and KAl(SO4)2 are characterized by X-ray and neutron powder diffraction at temperatures between 1.4 and 773 K. The compounds all crystallize in the space group P-3, with octahedral coordination of the trivalent cations. In all cases, small amounts of disorder in the stacking of the triangular layers of corner sharing MO6 octahedra and SO4 tetrahedra is seen, with the MO6-SO4 network rotated in opposite directions between layers. The electron diffraction study of KCr(SO4)2 supports this model, which on average can be taken to imply trigonal prismatic coordination for the M3+ ions; as was previously reported for the prototype anhydrous alum KAl(SO4)2. The temperature dependent magnetic susceptibilities for ACr(SO4)2 (A = K,Rb,Cs) indicate the presence of predominantly ferromagnetic interactions. Low temperature powder neutron diffraction reveals that the magnetic ordering is ferromagnetic in-plane, with antiferromagnetic ordering between planes below 3 K.Comment: Accepted to the Journal of Solid State Chemistr

Institutionalization of social and behavioral risk factor surveillance as a learning system

Objectives: This paper extends further the systematic nature of social and behavioral risk factor surveillance by showing how it becomes a learning system. The authors argue that such a systematic approach will lead to a better informed public health practice and a better understand of key public health concerns such as obesity. Methods: This paper is based on methods developed over some 25 years of experience in designing and operating behavioral risk factor surveillance systems. Measurement issues still remain a key concern and special attention is paid to the role of time as a critical variable in developing a surveillance system. Results: The paper lays out five critical areas for attention if a system is to be considered a learning system. Examples are given from ongoing surveillance systems that have developed a base for a learning system and notes how these are institutionalized. Conclusion: In the ideal case a learning system based on sociobehavioral surveillance is dependent on data being collected continuously with careful attention paid to the analytical challenges of such complex data. This is an ideal systematic approach that has not been realized in most surveillance systems now available

Anti-permissive attitudes to lifestyles associated with AIDS

AIDS is in the tradition of diseases which have given moral interpretations. One way in which this moralistic perspective may express itself is by members of the public holding high risk groups responsible for their (AIDS related) lifestyles and their considering AIDS to be a self-inflicted disease. A unique data source of 7000 verbatim comments recorded in the course of 25,000 structured Computer Assisted Telephone Interviews on Lifestyle and Health which contain a substancial component on AIDS--knowledge, attitudes, beliefs and sexual behaviour, was used to document negative attitudes to 'AIDS related lifestyles'. These comments revealed that despite evidence of concern about drug use, many respondents consider AIDS to be irrelevant to the majority of the population. There is some evidence that AIDS has contributed to reinforcing negative attitudes towards homosexuality and drug use, especially among older respondents. Extreme punitive attitudes towards high risk groups were expressed by a small minority (predominantly males).AIDS lifestyle attitudes stigma