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  • 1
    Electronic Resource
    Electronic Resource
    Effects of high vacancy concentrations on the magnetic properties of La1−xMn1−yO3 (0.02≤x, y≤0.13) (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 394-399 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It has been found that the synthesis conditions and subsequent annealing treatments can significantly change the magnetic and transport behavior of the colossal magnetoresistive materials of the general formula La1−zAzMnO3, where A is a divalent ion. In order to clarify the role of vacancies within this structure, resistivity and magnetization measurements have been carried out on a series of samples derived from the parent compound LaMnO3, with La and Mn vacancies introduced by systematically varying the oxygen annealing conditions. Previous studies have shown that for a given carrier concentration, the Curie temperature of the paramagnetic to ferromagnetic transition (Tc) increases as the tolerance factor of the perovskite structure increases and then begins to decrease slowly for even higher tolerance factors. Generally, Tc also increases with the Mn4+ content, consistent with a double exchange mechanism responsible for ferromagnetism. In this study Tc was found to decrease as the vacancy concentration (and therefore the Mn4+ concentration) and tolerance factor both increase. The magnetic and transport data are discussed in the light of structural information obtained from neutron diffraction studies. In the present study it is found that La and Mn vacancies play a significant role in determining the physical properties of these materials: for high vacancy concentrations (x,y≥0.080) the magnetic properties are analogous to those of spin glasses associated with disorder and frustration. Semiconductorlike resistivity was observed for all samples at all temperatures. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366653
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  • 2
    Electronic Resource
    Electronic Resource
    Mapping the multiple self-healing squamous epithelioma (MSSE) gene and investigation of xeroderma pigmentosum group A (XPA) and PATCHED (PTCH) as candidate genes (1997)
    Springer
    Human genetics 〈Berlin〉 101 (1997), S. 317-322 
    Details
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The MSSE gene predisposes to the development of multiple invasive but self-healing skin tumours (multiple self-healing squamous epitheliomata, MSSE). MSSE (previously named ESS1) was mapped to chromosome 9q by linkage analysis; haplotype analysis in families then suggested a common founder mutation and indicated that the gene lies in the interval D9S1–D9S29 (9q22–q31). Squamous cell carcinomata also develop as one of the complications of xeroderma pigmentosum, and one of the xeroderma pigmentosum genes (XPA) maps within the MSSE interval. We have investigated the hypothesis that a novel dominant mutation in XPA is responsible for MSSE. We screened the entire coding region, 3′ untranslated region (UTR) and 5′UTR of XPA for germline mutations in MSSE families by single-stranded conformation polymorphism analysis and by direct DNA sequencing. No mutations were detected but a novel intragenic polymorphism was identified in the 5′UTR of XPA, in both MSSE-affected and unrelated normal individuals. This XPA polymorphism and nine new polymorphic markers that map in the MSSE region were typed in eleven MSSE families; XPA was excluded as the MSSE gene and the most likely location of MSSE was reduced to the interval between D9S197 and (D9S287, D9S1809). The Patched (PTCH) gene, which is mutated in naevoid basal cell carcinoma syndrome (NBCCS or Gorlin syndrome) lies in this interval and all MSSE families have been shown to share a common haplotype at three novel intragenic PTCH polymorphisms. Although no mutation has been detected in MSSE families, PTCH has not been excluded as the MSSE gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004390050635
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  • 3
    Electronic Resource
    Electronic Resource
    Protein stability: still an unsolved problem (1997)
    Springer
    Cellular and molecular life sciences 53 (1997), S. 790-802 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Protein structure; packing; cavities and stability.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. This brief review suggests that molecular packing, the efficient filling of space, may be the most generally applicable factor that leads to the unique structures of most globular proteins. While simple in concept, the details of packing can lead to very subtle effects. The mechanical properties of a protein, dynamics and deformations under stress, tend to be asymmetric. In terms of structural alterations and thermostability, responses to genetic mutations are context dependent and remain difficult to predict with any confidence. Through small shifts proteins can frequently accommodate major changes in composition of the core region without substantial alteration in the basic chain conformation. Extending a jigsaw puzzle analogy, all of the pieces (side chains) are convex, varying flexible, and cannot be packed together without leaving cavities. Although large cavities do occasionally occur, a relatively even distribution of empty space is more common, and the overall packing does seem to specify the unique native structure. While it might appear that the translation machinery of the cell could have been designed with any set of α amino acids, the packing requirements, while strong, must be flexible enough to permit nondestructive single site mutations. This flexibility, combined with the need to produce a unique structure, may limit the average number of allowed side chain rotamers per residue. This in turn will reduce the allowable asymmetry of the side chains in order to maintain the largest number of structural motifs. It may be hard to improve on current set of amino acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000180050100
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