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  • 1
    Electronic Resource
    Electronic Resource
    Structure and Mössbauer spectroscopy of barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 between 80 K and 300 K (2000)
    Springer
    Physics and chemistry of minerals 27 (2000), S. 419-429 
    Details
    ISSN: 1432-2021
    Keywords: Key words Barbosalite ; Iron phosphate ; Structure refinement ; Mössbauer spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Natural barbosalite Fe2+Fe3+ 2 (PO4)2(OH)2 from Bull Moose Mine, South Dakota, U.S.A., having ideal composition, was investigated with single crystal X-ray diffraction techniques, Mössbauer spectroscopy and SQUID magnetometry to redetermine crystal structure, valence state of iron and evolution of 57Fe Mössbauer parameter and to propose the magnetic structure at low temperatures. At 298 K the title compound is monoclinic, space group P21/n, a o  = 7.3294(16) Å, b o  = 7.4921(17) Å, c o  = 7.4148 (18) Å, β = 118.43(3)°, Z = 2. No crystallographic phase transition was observed between 298 K and 110 K. Slight discontinuities in the temperature dependence of lattice parameters and bond angles in the range between 150 K and 180 K are ascribed to the magnetic phase transition of the title compound. At 298 K the Mössbauer spectrum of the barbosalite shows two paramagnetic components, typical for Fe2+ and Fe3+ in octahedral coordination; the area ratio Fe3+/Fe2+ is exactly two, corresponding to the ideal value. Both the Fe2+ and the Fe3+ sublattice order magnetically below 173 K and exhibit a fully developed magnetic pattern at 160 K. The electric field gradient at the Fe2+ site is distorted from axial symmetry with the direction of the magnetic field nearly perpendicular to Vzz, the main component of the electric field gradient. The temperature dependent magnetic susceptibility exhibits strong antiferromagnetic ordering within the corner-sharing Fe3+-chains parallel to [101], whereas ferromagnetic coupling is assumed within the face-sharing [1 1 0] and [−1 1 0] Fe3+-Fe2+-Fe3+ trimer, connecting the Fe3+-chains to each other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002699900078
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  • 2
    Electronic Resource
    Electronic Resource
    Studies of aging in ames dwarf mice: Effects of caloric restriction (2000)
    Springer
    Age 23 (2000), S. 9-16 
    Details
    ISSN: 1574-4647
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Ames dwarf mice, which are small and deficient in growth homone (GH), prolactin (PRL), and thyroid stimulating hormone (TSH) live much longer (1–1.25 years) than their normal siblings. It was of interest to examine the response of these animals to caloric restriction (CR) because of the possibility that dwarf mice are voluntarily caloric restricted. We are testing the hypothesis that this possible natural caloric restriction will negate any benefits of an imposed CR on lifespan. Male and female Ames dwarf mice and their normal counterparts have been fed ad libitum (AL) or a 30% CR diet for 25–29 months. Animals were monitored daily and weighed weekly. At 12–15 months of age, CR mice weighed significantly less than their AL fed counterparts (normal females: −42%, normal males: −23%, dwarf females: −18.8%, and dwarf males: −22.2%). Only in dwarf females has this significant difference disappeared with age. At one year of age, a comparison of daily food consumption revealed that female dwarf mice consume significantly more food per gram body weight than normal females and a similar tendency is evident for males. Although they received 30% less food, CR mice ate the same amount as AL mice per gram body weight. On measures of total locomotor activity, CR mice were significantly more active than their AL-fed counterparts. On an inhibitory avoidance learning task, 18–21 month old dwarf mice exhibited significantly better retention than their age-and diet-matched normal counterparts. Histopathological analysis in aging dwarf versus normal mice suggested that the incidence of tumors does not differ between the two groups but tumors appear to develop later in dwarf than in normal mice. After 2.25 years on the study 27% of AL normals, 52% of CR normals, 74% of AL dwarfs, and 87% of CR dwarfs are still alive. We conclude that Ames dwarfs are not CR mimetics although they share many characteristics. It remains to be determined whether CR will delay aging and cause a further life extension in Ames dwarf mice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s11357-000-0002-0
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    Paper (German National Licenses)
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