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  • 1
    Electronic Resource
    Electronic Resource
    A new computer program for Rietveld analysis of X-ray powder diffraction patterns (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 149-151 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Rietveld [J. Appl. Cryst. (1969), 2, 65–71] method of structure refinement from powder diffraction patterns is widely used with neutron data and increasingly so with X-ray data. A computer program for the application of the method with X-ray data, or with neutron nuclear scattering data, has been written ab initio in an effort to make it versatile, user oriented, portable, convenient, and largely self-contained yet reasonably comprehensive. It is of modular construction to facilitate user-desired modifications, one of which may be additions to the choice of four profile functions now included. The program accommodates either one or two wavelengths (e.g. α1 and α2 or λ and λ/2). It permits simultaneous refinement of the structures of two phases and the background.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889881008996
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  • 2
    Electronic Resource
    Electronic Resource
    Profile shape functions in Rietveld refinements (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 430-438 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Reflection profile functions used or suggested for use in Rietveld refinements with fixed-angle or fixed-wavelength powder diffraction data, obtained with neutrons or with X-rays, are reviewed briefly. The fixed-wavelength X-ray case is considered in detail. In tests of fitting to individual resolved reflection profiles, at least eight different profile functions, including some representations consisting of "learned' differentiable number arrays, have been show to be satisfactory at the less than 3% misfit level. Several authors have made comparative studies of subsets of the six analytic functions, Gaussian (G), Lorentzian (L), modified Lorentzian (ML), intermediate Lorentzian (IL), pseudo-Voigt (p-V), and Pearson VII (PVII). In this work, the performance of all six, in Rietveld refinements with data sets from seven different specimens with differing degrees of broadening, have been intercompared on the basis of difference plots, Rwp, and RB. The Gaussian function was consistently the worst performer, while the pseudo-Voigt and Pearson VII were the best. For this reason, for reasons of simplicity, and for convenient though crude physical interpretation of the Lorentz-fraction parameter, the pseudo-Voigt is identified as the function of choice among these six. It is emphasized that a need still exists for a better profile function soundly based on physical reality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988201231X
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  • 3
    Electronic Resource
    Electronic Resource
    Structure of partially substituted chlorapatite (Ca2Sr)5(PO4)3Cl (1980)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 36 (1980), S. 1525-1530 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740880006516
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  • 4
    Electronic Resource
    Electronic Resource
    Suggested guidelines for the publication of Rietveld analyses and pattern decomposition studies (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 15 (1982), S. 357-359 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889882012138
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  • 5
    Electronic Resource
    Electronic Resource
    Role of acid phosphate in hydroxyapatite lattice expansion (1984)
    Springer
    Calcified tissue international 36 (1984), S. 60-63 
    Details
    ISSN: 1432-0827
    Keywords: Human tooth enamel ; a axis ; HPO4 ; Structural H2O
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Questions remain about which subcomponents of human tooth enamel (TE) are responsible for its crystallographica axis being nearly 0.02Å longer than that of pure hydroxyapatite (OHAp) and contracting to that of OHAp on heating. From infrared spectroscopic and X-ray diffraction studies of a synthetic OHAp containing HPO4 and “structural” H2O, it has been concluded that HPO4 expands thea axis at the rate of ∼ 0.0015Å/ wt % but that this accounts for substantially less than one-half of the total observable contraction. The remaining, more than one-half of thea axis change, may be only partially ascribable to “structural” H2O and partially to P2O7 (formed from the HPO4), coming out of solid solution in the apatite. Some 90% of the HPO4 observed with infrared is lost in the 160–240° temperature range and more than one-half of the P2O7 observed as a separate phase is developed above that temperature and continues to increase all the way up to the 500°C, the limit of the experiments. The loss of HPO4 is accompanied by reduction of disorder or variety in the structural OH ion sites, consistent with the view that initially some of the PO4 groups neighboring the OH ions were actually HPO4 groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02405294
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal decomposition of human tooth enamel (1980)
    Springer
    Calcified tissue international 31 (1980), S. 189-201 
    Details
    ISSN: 1432-0827
    Keywords: Tooth enamel ; Thermal decomposition ; Water ; CO3 ; Hydroxyl
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Further insight into human tooth enamel, dense fraction (TE), has been obtained by following the change and loss of CO3 2−, OH−, structurally incorporated H2O, Cl−, and, indirectly, HPO4 2− after TE had been heated in N2 or vacuum in the range 25–1000°C. Quantitative infrared spectroscopic, lattice parameter, and thermogravimetric measures were used. Loss of the CO3 2− components begins at much lower temperature (e.g., 100°C) than previously recognized, which has implications for treatments in vitro and possibly in vivo. CO3 2− in B sites is lost continuously from the outset; the amount in A sites first decreases and then increases above 200° to a maximum at ∼800°C (〉10% of the possible A sites filled), where it is responsible for an increase ina lattice parameter. A substantial fraction of the CO3 2− in B sites moves to A sites before being evolved, apparently via a CO2 intermediary. This implies an interconnectedness of the A and B sites which may be significant in vivo. No loss of Cl− was observed at temperatures below 700–800°C. Structural OH− content increases ∼70% to a maximum near 400°C. Structurally incorporated water is lost continuously up to ∼800°C with a sharp loss at 250–300°C. The “sudden”a lattice parameter contraction, ∼0.014Å, occurs at a kinetics-dependent temperature in the 250–300°C range and is accompanied by reordering and the “sharp” loss of ∼1/3 of the structurally incorporated H2O. The hypothesis that structurally incorporated H2O is the principal cause of the enlargement of thea lattice parameter of TE compared to hydroxyapatite (9.44 vs 9.42Å) is thus allowed by these experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02407181
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  • 7
    Electronic Resource
    Electronic Resource
    Reversible high temperature exchange of carbonate and hydroxyl ions in tooth enamel and synthetic hydroxyapatite (1981)
    Springer
    Journal of biological physics 9 (1981), S. 1-26 
    Details
    ISSN: 1573-0689
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Parallel experiments on human tooth enamel with sp.g. 〉2.95 and synthetic hydroxyapatite have been carried out to study the substitution of CO 3 2− for OH−, produced at 1000°C in dry CO2, with the complementary use of neutron diffraction, x-ray diffraction, infrared spectroscopy and thermochemical techniques. It was verified that the substitution (i) is CO 3 2− ↔ 2(OH− and is completely reversible on specimen exposure to H2O vapor at 1000°C, (ii) takes place with the carbon atom on or near the hexad axis, (ii) places one CO 3 2− group per unit cell in an ordered fashion and so changes the space group fromP6 3/m to one without a screw axis, (iii) was consistent, by its incompleteness, with the occurrence of substitution of O2− for 2(OH−) in 25 to 40% of the unit cells, (iv) produced similar marked changes in the neutron powder diffraction patterns of both tooth enamel and hydroxyapatite, and (v) took place at a site where only a minor portion of the CO 3 2− in normal untreated human tooth enamel occurs. From comparative Rietveld analysis results from x-ray and neutron powder diffraction patterns it is suggested that the carbon atom of this A-site CO 3 2− is near 0,0,0.12 and the CO 3 2− plane makes an angle of ≈18° with thec direction. On being heated at 400°C in H2O vapor, tooth enamel retained much of its CO 3 2− but its a lattice parameter changed from 9.445(3) Å to 9.420(1) Å, essentially that of hydroxyapatite. After once being heated at high temperatures, “tooth enamel” and hydroxyaptite showed similar responses to various treatments, including carbonation. After heating, more β-Ca3(PO4)2 was found in the tooth enamel specimen. Comparative weight change, IR, and other data for tooth enamel and hydroxyapatite heated in He, then in CO2, and then in H2O vapor showed a 20% or more deficiency of structural OH− in the untreated tooth enamel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01987170
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  • 8
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    Efficient isolation of genes by using antibody probes. (1983)
    National Academy of Sciences
    Details
    Publication Date: 1983-03-01
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 9
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    Global and Hox-specific roles for the MLL1 methyltransferase (2005)
    National Academy of Sciences
    Details
    Publication Date: 2005-06-07
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Coordinated binding of NF- B family members in the response of human cells to lipopolysaccharide (2006)
    National Academy of Sciences
    Details
    Publication Date: 2006-04-04
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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