Synthesis, structure and geometrically frustrated magnetism of the layered oxide-stannide compounds Fe(Fe3-xMnx)Si2Sn7O16.

Fe4Si2Sn7O16 has a unique crystal structure that contains alternating layers of Fe(2+) ions octahedrally coordinated by O (oxide layer) and Sn (stannide layer), bridged by SiO4 tetrahedra. The formula can be written as FeFe3Si2Sn7O16 to emphasise the distinction between the layers. Here, we report the changes in structure and properties as iron is selectively replaced by manganese in the oxide layer. Solid-state synthesis was used to produce polycrystalline samples of Fe(Fe3-xMnx)Si2Sn7O16 for x≤ 2.55, the structures of which were characterised using high-resolution synchrotron X-ray and neutron powder diffraction. Single-crystal samples were also grown at x = 0.35, 0.95, 2.60 and characterised by single crystal X-ray diffraction. We show that manganese is doped exclusively into the oxide layer, and that this layer contains exclusively magnetically active high-spin M(2+) transition metal cations; while the stannide layer only accommodates non-magnetic low-spin Fe(2+). All samples show clear evidence of geometrically frustrated magnetism, which we associate with the fact that the topology of the high-spin M(2+) ions in the oxide layer describes a perfect kagomé lattice. Despite this frustration, the x = 0 and x = 2.55 samples undergo long-range antiferromagnetic ordering transitions at 3.0 K and 2.5 K, respectively.

The physical and chemical nature of technegas.

UNLABELLED: Technegas, the discrete radio-aerosol particle, containing 99mTc has been investigated, and the chemical evolution and physical properties of the particle demonstrated. METHODS: A commercial technegas generator was used to produce aerosols according to standard clinical procedures. The aerosols were collected by electrostatic precipitation and examined with transition electron microscopy (TEM), scanning electron microscopy (SEM) and force microscopy. The chemical evolution was examined by x-ray techniques and thermogravimetric analysis. RESULTS: The active particle was identified as hexagonal platelets of metallic technetium contained within a thin layer of graphitic carbon. This composite structure is discussed in light of the metal particle behaving as a template for the carbon capsule. The average size of the observed hexagonal platelets, 30-60 nm, was only weakly dependent on the concentration of technetium in the crucible. CONCLUSION: The mechanism for the formation of the technegas pancreas has been developed and the particles involved characterized. It appears that the use of other metals also leads to the formation of similar materials.

[Studies on nutritional effects of traditional Chinese tonics with strengthened nutrients on pregnant women and rats].

Clinical and Experimental studies on a mixture made of traditional Chinese tonics (such as Fructus Lycii, Rhizoma Dioscoreae and Arillus Longannae, etc.) and strengthened nutrients (such as iron, zinc and Calcium, etc.) were conducted in order to explore its nutritional and health promoting effects. (1) One hundred and three primiparous women were divided randomly into observed group and control group, results showed that the serum levels of iron, zinc, hemoglobin of observed group were all raised after treatment, these parameters and the concentration of iron in umbilical cord blood as well as body weight of new-born baby of the observed group were higher than that of control group (P < 0.05 or P < 0.01). (2) Results of experimental rats showed that the utilization rate, hemoglobin level, fetal growth and developing parameters of test group were all higher than that of control group significantly (P < 0.05 or P < 0.01). These results suggested that the nutrient mixture has a good nutritional and health promoting effect on pregnancy.

Frustrated magnetism and local structural disorder in pyrochlore-type Bi1.89Fe1.16Nb0.95O6.95.

The magnetic properties of pyrochlore-type Bi(1.89)Fe(1.16)Nb(0.95)O(6.95) have been investigated for the first time using AC and DC susceptibility. The compound is shown to behave as a classical spin glass due to strong competition/coexistence of ferro- and antiferromagnetic exchange. The study was accompanied by the first-ever growth of single crystals of this compound using the floating-zone method, allowing us to carry out a single-crystal neutron diffraction experiment that confirmed and extended our understanding of local structural disorder, driven by the stereochemically active 6s(2) electron lone pair on Bi(3+) ions. The magnetic properties are discussed in terms of both the topologically frustrated Fe(3+) lattice and the role of this local structural disorder.

Glass transition in the polaron dynamics of colossal magnetoresistive manganites.

Neutron scattering measurements on a bilayer manganite near optimal doping show that the short-range polaron correlations are completely dynamic at high T, but then freeze upon cooling to a temperature T(*) approximately equal 310 K. This glass transition suggests that the paramagnetic/insulating state arises from an inherent orbital frustration that inhibits the formation of a long-range orbital- and charge-ordered state. Upon further cooling into the ferromagnetic-metallic state (T(C) = 114 K), where the polarons melt, the diffuse scattering quickly develops into a propagating, transverse optic phonon.

Colorectal cancer in Chinese and Chinese-Americans.

Rationale and plans are described for a collaborative case-control study of large bowel cancer among Chinese-Americans in Los Angeles and the San Francisco Bay Area and among Chinese in Zhejiang Province, People's Republic of China. A common protocol and questionnaire will be used during personal interviews of approximately 400 Chinese and 300 Chinese-American patients with histologically confirmed adenocarcinoma of the colon or rectum and 2,100 Chinese and Chinese-American controls. Controls will be matched to patients on age, sex, and community of residence. The information requested from subjects will permit testing of hypotheses relating colorectal cancer risk to: dietary factors, including intake of fat (saturated and unsaturated), animal protein, fiber, and vitamins A and E and ascorbic acid; physical activity levels and body mass index; reproductive factors among women; history of bowel disease; and family history of cancer. The information requested of Chinese-American subjects will also permit testing of hypotheses relating cancer risk to such migrant factors as United States versus Chinese nativity, duration of residence in the United States, and Chinese province of ancestry. These factors will be tested for associations with cancers of the colon and rectum separately and with cancers of the large intestine as a whole. We will examine sex and geographic differences in relative risks for etiologic factors, location of tumors within the large bowel, histologic subtype of adenocarcinoma, and frequency of accompanying polyps.