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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 477-482 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The stacking sequence of a new SiC polytype 45Rb, which was synthesized at room temperature is (433212)3. This implies that the Zhdanov symbol 1 in the stacking sequence, except for the 2H polytype, might be a special characteristic of the structure of SiC grown at low temperatures. If this is true, the recently reported 5H polytype SiC found in limestone, dolomite and alluvial deposit, which can be deduced as (41) stacking, may be authigenic and might have grown at a low temperature. This idea may suggest the general distribution of SiC in limestone and in other low- temperature deposits. Unmetamorphosed limestones of about 20 localities were examined, and SiC was found in seven of those localities, although the 45Rb and 5H polytypes have not been found yet in these samples.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 138 (1986), S. 1110-1115 
    ISSN: 0006-291X
    Keywords: [abr] ARS; autonomously replicating sequence ; [abr] EtBr; ethidium bromide ; [abr] kb; kilobase pairs ; [abr] mt; mitochondrial
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 138 (1986), S. 1110-1115 
    ISSN: 0006-291X
    Keywords: [abr] ARS; autonomously replicating sequence ; [abr] EtBr; ethidium bromide ; [abr] kb; kilobase pairs ; [abr] mt; mitochondrial
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    BBA Section Nucleic Acids And Protein Synthesis 269 (1972), S. 376-384 
    ISSN: 0005-2787
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 2438-2438 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In the field of material sciences, it has long been desired to develope the equipment to obtain crystallographic information of micrometer-size crystalline substances. Synchrotron radiation (SR) could be a candidate to deal with such a small specimen other than electron microscope. It seems more advantageous to utilize SR from the viewpoint that the processing of the diffraction data that has already been established for identification of the materials, structure analysis, and refinement. Even in the case of SR, special care should be taken for the measurement of very weak diffracted intensities. In the case not using SR, the size of 50 μm might be the limit for the specimen to be examined by the diffraction method. The diffracted intensity is proportional to the volume of the specimen, and that of micrometer-size crystal is estimated as 10−5 times of that of the limit mentioned above. The noise level of the experiment, therefore, should be as low as possible. If the noise level becomes negligibly small, the signal could be accumulated continually to the desired intensity level by adjusting measuring time. The experiment, for the purpose, should be carried out in vacuum with the stational crystal method and with very narrow collimated x-ray beams.The Laue method is employed by the above reason, as well as the fact that the intensity of each Bragg reflection on a reciprocal row passing through the origin of the reciprocal space is superposed with each other, which also intensifies a diffraction spot on the photographic plate. The Laue camera is set up at BL-4B of Photon Factory, sealed in vacuum and installed with a very narrow collimater. The development of the system has been performed to the level which several Bragg reflections of molybdenum single crystal with 0.8 μm in its diameter can be taken on the imaging plate for 50-min exposure with ring current from 128 to 125 mA. The origin of diamonds in meteorites has been a controversy as to whether they are formed from carbonaceous materials by impact shock or directly formed from vapor. Recent discovery of vapor-growth diamonds in carbonaceous chondrites has generated a renewed interest in the origin of ureilite diamonds. Two types of micrometer-size diamonds were prepared. One of them was grown under low pressure by chemical vapor deposition (CVD) from gaseous mixtures of H2 and CH4, and another was synthesized by shock effect (kindly offered by Nippon Oil & Fats Co., Ltd.) The micro-Laue method was applied to them in order to get information about their microstructures. Two characteristics are recognized in profiles of reflections themselves and in whole patterns of the Laue photographs. The reflections of CVD diamonds are elongated but symmetric in their profiles and are distributed regularly as they are indexed by the diamond lattice, while those of shock effect are also elongated and asymmetric, and are distributed at random as they cannot be indexed. The characteristics observed by the method may be useful to ascribe the origin to CVD or shock effect.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In order to study the process of reaction in crystals, it is necessary to observe decomposition of precursor and formation of the product during the transformation. Since such change is related to the structures of both the phases, x-ray diffraction is the most powerful method for this purpose. However, not only Bragg reflections but diffuse scattering or satellite reflections are observed occasionally in the early stage of the process and intensities of those scattering are extremely weak although they are important to analyze the process. Therefore, use of synchrotron radiation is desirable to study those problems. There are many compounds which show topotaxy during phase transformation. Since the product of such transformation is formed in an oriented manner under the influence of the structure of the precursor, diffraction patterns of the product are similar to those of a single crystal and anomaly of the diffraction can be easily detected. We have consequently studied the process of dehydration in α-AlOOH which indicates topotaxy in the process of dehydration. α-AlOOH transforms to α-Al2O3 at about 500 °C when it is heated in air. Lima-de-Faria (1963) found that the products revealed distinct satellite reflections along c* direction on x-ray diffraction patterns when the samples are quenched to room temperature in the early stage of reaction. Similar phenomena are also known in dehydration of α-FeOOH to α-Fe2O3 (both of them are isostructural to α-AlOOH and α-Al2O3, respectively). No interpretation has yet been established to the origin of the satellites. We have analyzed the averaged structure, interpreted the satellite reflections and change of profile of the satellites, and have elucidated the process of the reaction. The results indicate that the origin of the satellites is ascribed to the modulation of Al content along c direction and the change of the profile to the change in the mode of the modulation.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system for analyzing and refining the crystal structure of a submicrometer-sized specimen has been developed at the Photon Factory, KEK, employing a Laue method with an imaging plate. The system was evaluated using two molybdenum spheres with diameters of 0.8 μm and 0.27 μm3 in volume. The result showed that the isotropic temperature factors of both spheres were successfully refined, and that one of the samples was found to be twinned. The smaller domain of the twin was determined to be 0.02 μm3 in volume, which means that the smaller domain is composed of only 109 Mo atoms. The system was applied to a 5-μm-sized icosahedral CVD diamond as a first application. Analysis of several Laue patterns revealed that the sample is composed of more than 17 domains. Among them, 16 domains are twinned with each other, and the mode of twinning is of the spinel twin type.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 254-258 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Laue classes of powder diffraction data for tetragonal, hexagonal and cubic crystal families can be derived from interpretation of the concentration of peaks in Patterson functions that are transformed from weighted reciprocal lattices constructed with diffraction data of polycrystalline materials [Ohmasa & Ohsumi (1995). Acta Cryst. A51, 87–91 ]. The method was applied to powder diffraction data of α- and β-quartz, and discrepancies of concentrations of the peaks in both Patterson functions were detected, although the difference of their structures is caused by small shifts of the atomic positions.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 340-348 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A system has been developed for the analysis of the structure of a submicrometer-sized single-crystal using synchrotron radiation (SR) at the Photon Factory (PF), KEK. The Laue method combined with an imaging plate was employed for the collection of diffracted intensities. To reduce background, the experiment was carried out in a vacuum and with a very thinly collimated incident X-ray beam. The system has been shown to reach a level where a molybdenum sphere with diameter as small as 0.8 μm was found to be twinned and the volume ratio of the twin domains was determined, together with an isotropic temperature factor, which was comparable with the value determined in the same experiment on another single-crystal sphere of almost the same size. It was in good agreement with that determined by a powder diffraction study. The present study showed that any single-crystal detectable under an optical microscope can be analysed and, further, that the diffraction intensities from a crystal with volume of 0.02 μm3, which is composed of 109 atoms, can be detected.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 56 (2000), S. 811-821 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The incommensurate structure of (Sr0.13Ca0.87)2CoSi2O7 at room temperature has been determined from single-crystal X-ray diffraction data. The compound has a non-centrosymmetric tetragonal basic cell of a = 7.8743 (4) and c = 5.0417 (2) Å with the space group P4¯21m. The refinements of the basic structure converged to R = 0.038 for 757 main reflections. The two-dimensional incommensurate structure is characterized by the wavevectors q1 = 0.286 (3)(a* + b*) and q2 = 0.286 (3)(−a* + b*), where a*, b* are the reciprocal lattice vectors of the basic structure. With the (3 + 2)-dimensional superspace group Pp4mgP4¯21m, the refinements converged to R = 0.071 for 1697 observed reflections (757 main and 940 satellite reflections). The structure is described in terms of displacement of the atoms, rotation, distortion of CoO4 and SiO4 tetrahedra, and the partial ordering of the Sr and Ca atoms accompanied with the modulation. Correlated evolution of these features throughout the crystal gives rise to various oxygen coordination around Ca/Sr. Comparison of the derived modulated structure to that of Ca2CoSi2O7 clarified that the partial substitution of Ca by large alkaline-earth atoms such as Sr should decrease the distortion of the polyhedra around the cations.
    Type of Medium: Electronic Resource
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