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  • 1
    Electronic Resource
    Electronic Resource
    On the nature of grown-in defects in topaz (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 177-182 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A study has been made of crystals of topaz by optical and interference microscopy, X-ray topography, and scanning and transmission electron microscopy. Most of the samples show a nearly perfect region with dislocation density ̃102 cm-2 surrounded by a highly defective narrow rim containing dislocations (density ̃107 cm-2 and higher), low-angle boundaries, networks and planar faults. The Burgers vectors of the dislocations observed in both regions of the crystal have been determined by means of diffraction contrast experiments and the nature of other defects is considered in detail. The relevance of the defects to the anomalous optical properties of the rim is discussed. A direct correlation between etch pits and dislocations in (001) sections of topaz is shown and evidence is presented that screw dislocations or even those with an appreciable screw component are not required for the formation of curl-bottomed pits. The origin of curl-bottomed pits is explained. It is suggested that the sudden increase in the density of dislocations in the rim is due to heterogeneous nucleation of dislocations by local internal stresses in growth layers which have been poisoned by increased impurity concentrations during growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000442
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  • 2
    Electronic Resource
    Electronic Resource
    Visualisation of micropore structure in human dental enamel (1974)
    [s.l.] : Nature Publishing Group
    Nature 252 (1974), S. 584-585 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fig. 1 Transmission electron micrograph of longitudinal section of ion beam thinned human dental enamel showing the long lath structure of apatite crystals with electron lucent channels or pores between them. Ion beam thinning may remove organic material faster than the mineral phase but because it ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/252584a0
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  • 3
    Electronic Resource
    Electronic Resource
    Ultrastructural changes in the translucent and dark zones of early enamel caries (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral pathology & medicine 9 (1980), S. 0 
    Details
    ISSN: 1600-0714
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract Selected areas of early enamel caries (‘White spot’ lesion) in human teeth were argon-ion-beam thinned and examined by transmission electron microscopy. A systematic examination of areas which were histologically defined as the translucent zone and the dark zone showed that the pattern of early caries was consistent with that of demineralization of the tissue commencing with a widening of the micropores and of the inter-rod spaces and gradually progressing to a severe destruction of the original enamel crystals, with possibly some remineralization. Observations indicate that the intercrystalline micropores and inter-rod spaces are the pathways by which acidic agents reach the crystals causing carious dissolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0714.1980.tb01387.x
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  • 4
    Electronic Resource
    Electronic Resource
    Laminated zones in carious human dental enamel (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral pathology & medicine 15 (1986), S. 0 
    Details
    ISSN: 1600-0714
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract Laminated zones within the body of carious lesions were studied by polarized light microscopy and transmission electron microscopy. Areas from within and surrounding the laminated zones, precisely selected using light microscopy, were argon-ion-beam thinned and examined by transmission electron microscopy. Laminated zones were present in ∼7% of the samples studied. Polarized light microscopy showed variation in mineralization from zone to zone and the enamel surrounding the zones in the body of the lesion. Laminated zones whose central region showed ∼1% of space when examined in air and whose boundaries showed ∼2–4% of space when imbibed in quinoline were selected for ultrastructural studies. Electron microscopy showed the laminated zone to be less demineralized than the surrounding enamel in the body of the lesion. The ultrastructure of their central regions was similar to healthy enamel but their boundaries showed demineralization which increased into the body of the lesion. Within the central region of lamination there was greater evidence of resistance to demineralization rather than the presence of remineralization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0714.1986.tb00587.x
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  • 5
    Electronic Resource
    Electronic Resource
    Ultrastructure of the intact surface zone of white spot and brown spot carious lesions in human enamel (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of oral pathology & medicine 15 (1986), S. 0 
    Details
    ISSN: 1600-0714
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Electron microscopy of the intact surface zone of white spot and brown spot carious lesions showed that in general their ultrastructure was similar. Their outermost crystalline surface consisted of small crystals similar to those in healthy enamel, crystals with central core dissolution, and rounded crystals. Below this, surface demineralization of enamel was observed as the enlargement of micropores, the central core dissolution of crystals, the formation of channels and the enlargement of spaces at prism boundaries. Remineralization of enamel was observed as the partial occlusion of voids, the rounding and enlargement of crystals, and some new needle-shaped crystals. Some other features indicated combined demineralization and remineralization. The occlusion of spaces at prism boundaries was a more common feature in brown spot lesions, whereas the pockets of rounded crystals were more common in white spot lesions. A relatively uniform distribution of needle-shaped crystals throughout the intact surface zone was a feature of some brown spot lesions only.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1600-0714.1986.tb00560.x
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  • 6
    Electronic Resource
    Electronic Resource
    Dislocations and fault surfaces in natural apatite (1970)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 3 (1970), S. 38-44 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The grown-in defects in gem quality crystals of natural apatite have been investigated using X-ray diffraction topography. The most common defects are the fault surfaces which are parallel to {10\overline 11} growth horizons, and these fault surfaces result from the incorporation of impurities during the growth of the crystal. The dislocation density of the crystals is low. A majority of these dislocations align with [0001] and have Burgers vector b = c[0001]. Some dislocations make about 15° with [0001] and have a Burgers vector with a c-axis component, probably b = \mida + c\mid〈12\overline 23 〉. A minority of the dislocations, nearly normal to the growth surfaces, have a mixed character with Burgers vector b = a〈11\overline 20〉.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889870005617
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  • 7
    Electronic Resource
    Electronic Resource
    A method of correlating dislocations and etch pits: application to cyclotrimethylene trinitramine (1971)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 4 (1971), S. 479-481 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A simple method to correlate dislocations observed in X-ray topographs with etch pits is described and has been applied to the case of cyclotrimethylene trinitramine crystals grown from solution by slow cooling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889871007490
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  • 8
    Electronic Resource
    Electronic Resource
    Defects in natural type IB diamond (1977)
    [s.l.] : Nature Publishing Group
    Nature 269 (1977), S. 227-229 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The thermal conductivity of IB diamond (specimens C8 and C9 in Fig. 1) was first measured in 19721 and subsequent experiments2'3 have produced similar results. It was found that the strength of the phonon scattering mechanisms which significantly reduced the IB conductivity as compared to purer IIA ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/269227a0
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  • 9
    Electronic Resource
    Electronic Resource
    Direct observation of anti-phase domain structure in omphacite (1973)
    Springer
    Contributions to mineralogy and petrology 39 (1973), S. 239-245 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Single crystal electron diffraction patterns of an omphacite (CaNa, Mg2+, Fe2+, Al3+, Fe3+)Si2O6 from a glaucophane schist facies (type C) eclogite, Tiburon Peninsula, California show weak reflections violating the C2/c space group. Transmission electron microscopy with dark field imaging, using h+k = even reflections reveal no special features, while dark field viewing through certain superstructure reflections violating the C2/c space group (h k l, with h+k = odd and h 0 l with h and/or l odd) reveal anti-phase domains, 100 to 3000 Å in width. Diffraction contrast experiments show that these domains are related by a displacement vector R=1/2[110]. This displacement vector explains the origin of the domains in terms of ordering of various cations in the octahedral (M1 type) and polyhedral (M2 type) sites without any changes in the tetrahedral silicate chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00383106
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  • 10
    Electronic Resource
    Electronic Resource
    Planar faults in dental hydroxy-apatite (1982)
    Springer
    Calcified tissue international 34 (1982), S. 209-210 
    Details
    ISSN: 1432-0827
    Keywords: Enamel ; crystallographic fault ; caries
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary There is a range of experimental evidence consistent with the existence of planar defects in the apatite crystals which constitute dental enamel. The evidence includes the appearance of crystals in the electron microscope both before and after attack by caries or caries-simulating etchants, the cross-sectional shape of the crystals and their long lath-like morphology. It is suggested here that the defects are twin planes in the apatite structure and it is further shown that such twin faults can form with only minor disturbance to the structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02411235
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