The current definition of samarskite-group minerals suggests that ishikawaite is a uranium rich variety of samarskite whereas calciosamarskite is a calcium rich variety of samarskite. Because these minerals are chemically complex, usually completely metamict, and pervasively altered, their crystal chemistry and structure are poorly understood. Warner and Ewing (1993) proposed that samarskite is an A 3+ B 5+ O 4 mineral with an atomic arrangement related to a-PbO 2 . X-ray diffraction analyses of the recrystallized type specimen of ishikawaite and the Ca-rich samarskite reveal that they have the same structure as samarskite-(Y) recrystallized at high temperatures. Electron microprobe analyses show that the only significant difference between samarskite-(Y), ishikawaite, and calciosamarskite lies in the occupancy of the A-site. The A-site of samarskite-(Y) is dominated by Y+REE whereas the A-site of ishikawaite is dominantly U+Th and calciosamarskite is dominantly Ca. Additionally, a comparison of these data to those of Warner and Ewing (1993) show that in several cases Fe 2+ or Fe 3+ are dominant in the A-site. We propose that the name samarskite-(REE+Y) should be used when one of these elements is dominant and that the mineral be named with the most abundant of these elements as a suffix. The name ishikawaite should be used only when U+Th are dominant and the name calciosamarskite should only be used when Ca is the dominant cation at the A-site. Finally, because of the inability to quantify the valence state of iron in these minerals, the exact nature of the valence state of iron in these minerals could not be determined in this study.
Autism spectrum disorder is a complex developmental disorder that dramatically affects the lives of patients and their families and the broader community. The causes of autism are unknown; however, evidence increasingly suggests that a complex interplay among environmental stressors, genetic mutations, and other biological factors likely plays a significant role in the development and/or progression of autism spectrum disorder. On April 18 and 19, 2007, the Institute of Medicine's Forum on Neuroscience and Nervous System Disorders hosted a workshop to provide a venue to bring together scientists; major sponsors of autism-related research; and members of the autism patient, family, and advocacy community to discuss the most promising and urgent scientific questions and opportunities. Broad participation by the autism community enriched the meeting significantly by contributing a valuable and personal perspective that is often missing from scientific meetings. It also began a much improved public-private partnership in which all stakeholders are represented. On the basis of the presentations and the discussions that followed, an array of important scientific opportunities were identified in 5 general categories: (1) opportunities to advance clinical research; (2) opportunities to enhance epidemiologic studies; (3) opportunities to improve the understanding of autism's pathology and etiology; (4) tools and infrastructure needs; and (5) opportunities for public-private partnerships. This workshop demonstrated that full public engagement can greatly enhance activities such as this workshop and its outcomes. Furthermore, we expect that this listing of scientific challenges, needs, and opportunities will help to frame a more comprehensive research agenda.
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