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  • Nature Publishing Group  (18,756)
  • National Academy of Sciences  (12,418)
  • American Physical Society (APS)
  • International Union of Crystallography (IUCr)
  • 1990-1994  (38,337)
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Publisher
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Molecular mimicry in liver disease (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 377-378 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR — Primary biliary cirrhosis (PBC), an autoimmune chronic cholestatic liver disease, affects mainly women and ulti-mately leads to the destruction of the intra-nepatic bile ducts and death from liver failure. The disease is characterized by the presence of diagnostic serum ...
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    URL: http://dx.doi.org/10.1038/358377a0
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  • 2
    Electronic Resource
    Electronic Resource
    Fact and fiction in alignment (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 271-271 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - We have discovered a startling similarity between a dinosaur DNA sequence reported in the novel Jurassic Park1 and a partial human brain cDNA sequence from the Venter laboratory described in Nature1 (see figure). The dinosaur sequence (Dinol) consists of duplication, with 117 base pairs from ...
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    URL: http://dx.doi.org/10.1038/358271c0
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  • 3
    Electronic Resource
    Electronic Resource
    Productivity drive (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 738-738 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - In a recent study on prolific productivity among prominent scientists (MedicalHypotheses, in the press), I have identified eight scientists who have been authors of more than 1,000 research publications, including books, monographs and patents as well as regular papers. They are, in ...
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    URL: http://dx.doi.org/10.1038/356738b0
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  • 4
    Electronic Resource
    Electronic Resource
    Folding in the egg white (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 278-279 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PROTEINS seem to find it easy to fold into their three-dimensional conformation - the difficulty is the scientist's, in failing so far to understand how they do it, let alone predict either the pathway or the end state. Three of the more important questions facing the protein folder are these. ...
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    URL: http://dx.doi.org/10.1038/358278a0
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  • 5
    Electronic Resource
    Electronic Resource
    'Neutral' CFCs? (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 738-738 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The suggestion1 that CFCs may be 'greenhouse neutral' on a global scale may bear on the negotiations at Rio de Janeiro in June aimed at reducing the potential for global warming. Although spatial variations of ozone concentration will complicate the argument2, at first sight the possibility ...
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  • 6
    Electronic Resource
    Electronic Resource
    Text analysis (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 740-740 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] ONE of the ma,m contributors to a text's difficulty js its pattern of word choice. In English, this choice is from an estimated 600,000 word-types {terms naving unique orthography), A tog-normal model1 of word choice predtcts that when the words from a large representative ...
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    URL: http://dx.doi.org/10.1038/356740a0
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  • 7
    Electronic Resource
    Electronic Resource
    The growing inaccessibility of science (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 739-740 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THERE is plenty of anecdotal evidence that large areas of the scientific literature are becoming incomprehensible to all but a few initiates. But how persuasive is anecdote? In this article I describe an objective way of looking at the matter and discuss its application to science journals over the ...
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  • 8
    Electronic Resource
    Electronic Resource
    Evolution of ecological differences in the Old World leaf warblers (1992)
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 176-176 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IN Fig. 2a of the above letter the second and third rows were inadvertently interchanged. In addition, the sequence at position 15176 (ref. 1.) for both Sylvia and P. coronatus should read 'A' and not ...
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    URL: http://dx.doi.org/10.1038/357176a0
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  • 9
    Electronic Resource
    Electronic Resource
    Guides to experiments (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 743-744 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] RNA EDITING is a bizarre and fascinating form of gene transcript maturation, in which uridine residues are post-transcriptionally inserted into (and occasionally deleted from) mitochondrial RNAs in trypanosomes and related organisms to achieve the mature messenger RNA sequence. The process accounts ...
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  • 10
    Electronic Resource
    Electronic Resource
    Deep ocean circulation puzzle (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 744-746 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] NOTIONS of the influence deep ocean circulation can have on the climate will have to be revised in the light of papers on pages 757 and 783 of this issue. Lehman and Keigwin1 and Veum et al.2 have examined tracers of ocean circulation in the northern corner of the North Atlantic and find that ...
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  • 11
    Electronic Resource
    Electronic Resource
    Peter Mitchell (1920 - 1992) (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 747-747 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PETER Mitchell, biochemist and Nobel laureate for chemistry in 1978, died from cancer on 10 April. Mitchell's single-minded purpose was to understand the mechanistic relationships between the metabolism of cells and the transport of solutes across cellular membranes. Clearly they were related, but ...
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    URL: http://dx.doi.org/10.1038/356747a0
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  • 12
    Electronic Resource
    Electronic Resource
    Proteases: to each his own (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 748-749 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PROCESSING of propeptides involves the cleavage of one or more peptide bonds in the inactive precursor resulting in a smaller, sometimes fragmented, active protein. Very often these processing enzymes are unique to a particular pro-peptide and possess unusual specificity aimed at a limited number ...
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    URL: http://dx.doi.org/10.1038/356748a0
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  • 13
    Electronic Resource
    Electronic Resource
    Why the recession is still here (1992)
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 1-1 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] FINANCE ministers, the people who decide what taxes we pay, behave even more curiously as a group than singly. The meeting of the finance ministers of seven industrialized nations of the world (known as G-7 for 'Group of Seven') in advance of the annual meeting of the International Monetary Fund ...
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    URL: http://dx.doi.org/10.1038/357001a0
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  • 14
    Electronic Resource
    Electronic Resource
    Structure and expression of a human oxytocin receptor (1992)
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 176-176 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] WE have discovered an error in the DNA sequence of our pOTR gene in Fig. \b. The nucleotides 714-717, CGGC should be GGCGGCG. The amino acids underneath should be Ala Ala Ala instead of Ala Gly. Accordingly, the complementary DNA encodes a 389 amino-acid protein with a relative molecular mass of ...
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  • 15
    Electronic Resource
    Electronic Resource
    Protein-DNA interactions at a yeast replication origin (1992)
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 169-172 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] All yeast ARSs contain an exact or close match to the core consensus sequence, 5'-A/TTTTATA/GTTTA/T-3' and this sequence seems essential for origin function. In addition to this element, flanking sequences are important for efficient ARS activity1'2. At ARS1, the core consensus sequence lies in a ...
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  • 16
    Electronic Resource
    Electronic Resource
    Molecular cloning of cDNAs encoding a guanine-nucleotide-releasing factor for Ras p21 (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 351-354 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] To clone a GRF for Ras p21, (Ras-GRF), we exploited the fact that GRFs for yeast RAS can activate mammalian Ras11-15. A set of degenerate oligonucleotides was designed to code for all peptides present in two highly conserved regions of three GRFs for yeast RAS, CDC25 (ref. 16) and SDC25 from S. ...
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    URL: http://dx.doi.org/10.1038/358351a0
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  • 17
    Electronic Resource
    Electronic Resource
    US drops Imanishi-Kari investigation; Baltimore withdraws Cell retraction (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 177-177 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Washington. US prosecutors announced this week that they are dropping their criminal investigation of Thereza Imanishi-Kari, a Tufts University immunologist accused of scientific misconduct, because the case is too complex and tangled for a jury to reach a conclusion. At the same time, David ...
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  • 18
    Electronic Resource
    Electronic Resource
    British military beckons environmental researchers (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 179-179 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] London. The British Ministry of Defence (MoD) is putting its people, equipment and real estate at the disposal of environmental researchers in a new initiative intended to benefit science. Researchers welcome the opportunity but are scratching their heads to understand such generosity. When the ...
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  • 19
    Electronic Resource
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    US rules out gene patent treaty (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 180-180 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Washington, The chief US science official said last week that the United States will abide by its controversial decision to file applications for patents on gene fragments and will not pursue an international treaty on the issue. D. Allan Bromley, science adviser to the president, said that the ...
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  • 20
    Electronic Resource
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    Chinese researchers promised more (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 182-182 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Beijlng. Prominent Chinese researchers last month heard their government's finance minister promise them more money-sometime. At a meeting on 17 June between Wang Bing-Ojan and the Chinese Academy of Sciences, the finance minister said that the government has adopted a policy, to be implemented ...
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  • 21
    Electronic Resource
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    Cost of brain disorders (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 184-184 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - I was distressed to read the leading article disparaging the report The Costs of Disorders of the Brain. This report argued that the estimated $401 billion annual costs for brain disorders in the United States justifies a substantial increase in funding for brain research. Nature did ...
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  • 22
    Electronic Resource
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    'Blue ostriches' captured (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 185-185 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The 'blue ostriches', a famous portrayal of a supposed rock painting, is very probably a forgery based upon an engraving (see top figure) in Moffat's Missionary Labour (1842)1. The 'copy' of the mysterious painting (middle fi-gure) was made by G. W. Stow, who was born in England in 1822 ...
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  • 23
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    How to publish the unpalatable? (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 187-187 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] How should a journal, this one perhaps, respond when asked to publish material that contradicts generally accepted views, that the Earth is a rough approximation to an ellipsoid for example? Or that Einstein's relativity is broadly correct (if not widely understood)? The proper response is that a ...
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  • 24
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    The big accelerator in the sky (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 189-190 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE positron, the antimatter counterpart of the electron, was discovered on 2 August 1932, dramatically and unex-pectedly confirming Dirac's new quan-tum theory of the electron. The positron in question was created by a cosmic ray which happened to end its wanderings around the Galaxy in ...
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  • 25
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    Cloning of cDNAs for Fanconi's anaemia by functional complementation (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 763-767 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fanconi's anaemia is a rare autosomal recessive disorder characterized by progressive pan-cytopaenia and a cellular hypersensitivity to DNA crosslinking agents. Four genetic complementation groups have been identified so far, and here we use a functional complementation method to clone ...
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  • 26
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    Superconductivity at 110 K in the infinite-layer compound (Sr 1-x Ca x ) 1-y CuO 2 (1992)
    [s.l.] : Nature Publishing Group
    Nature 356 (1992), S. 775-776 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Samples were prepared starting from metallic compositions of Cal_xSrx:Cu=l-iy:l with 0.4^x^0.7 and O^^^O.l. Typically, a gold capsule was filled with an intimate mixture of Ca0 3Sr0 7CuO2 (low-pressure phase) and fine powder of CuO, pressed almost isostatically up to 6 GPa using a classical ...
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  • 27
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    Sensing the potential (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 200-201 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] BIOSENSORS are portrayed in scientific and popular journals as having immense potential in medicine, clinical chemistry, environmental monitoring and defence. But the image of a biosensor as a miniaturized probe or hand-held 'black box' that provides instantaneous analy-tical results is, ...
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  • 28
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    Moscow, physics and beyond (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 201-202 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IGOR Tamm was one of the generation of Russian theoretical physicists who took what was a moribund and backward subject in their country to its present position of international prominence. From 1934 until his death in 1971 he was head of the theoretical physics depart-ment of the Lebedev ...
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  • 29
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    A double-sided radio jet from the compact Galactic Centre annihilator 1E1740.7–2942 (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 215-217 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] After the first observations with SIGMA, we initiated radio monitoring, at several wavelengths, of 1E1740.7-2942, the dominant hard X-ray source (&30keV) near the Galactic Centre4. The hard X-ray spectrum in its normal state resembles that of Cygnus X-l, one of the best candidates for ...
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  • 30
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    Variability in sea-ice thickness over the North Pole from 1977 to 1990 (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 224-226 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The Arctic Ocean is generally regarded as a potentially sensi-tive indicator of global change, especially as the predicted result of continued greenhouse-gas emissions is a global warming with high-latitude amplification1. Such a warming could thus have important consequences for the ...
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  • 31
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    Post-Jurassic mammal-like reptile from the Palaeocene (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 233-235 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Class Reptilia Subclass Synapsida Order Therapsida Suborder Cynodontia Chronoperatidae fam. nov. Type genus Chronopemtes gen. nov. Chronoperates paradoxus gen. et sp. nov. Etymology. Chronos (Greek): time; perates (Greek): wanderer, in reference to the geochronologic gap between this taxon ...
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  • 32
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    Nuclear localization and signalling activity of phosphoinositidase Cβ in Swiss 3T3 cells (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 242-245 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] An analysis of phosphoinositidase C (PIC) activities in the nucleus and cytoplasm of Swiss 3T3 cells using [3H]PtdInsP and [3H]PtdInsP2 as substrates is shown in Fig. 1. Both nuclear and cytoplasmic activities require calcium because the addition of EGTA completely abolishes breakdown. ...
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  • 33
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    Cytotoxic T-lymphocyte activation involves a cascade of signalling and adhesion events (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 253-255 
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    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Fluid-phase anti-TCR monoclonal antibody is not a sufficient stimulus to trigger degranulation by cloned cytotoxic T-lymphocytes (CTL), but primes the cells for CDS-dependent adhesion to class I protein, which results in triggering of degranulation3. To determine which signalling events ...
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  • 34
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    Nature; 358.1992, 6383, S.262 (1992)
    [s.l.] : Nature Publishing Group
    Nature 358 (1992), S. 262-262 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] PLEASE follow these guidelines so that your manuscript may be handled expeditiously. Nature is an international journal covering all the sciences. Contributors should therefore bear in mind those readers who work in other fields and those for whom English is a second language, and write clearly ...
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    Multiple scattering of X-rays in the case of isotropic samples (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 11-17 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The contribution of multiple scattering in wide-angle X-ray scattering experiments on isotropic samples using Mo Kα and Cu Kα radiation is estimated. The portion of doubly and triply scattered intensity was calculated with a tedious Monte Carlo simulation method and the portion of doubly scattered intensity was calculated with a fast approximate numerical integration procedure. In the case of light elements the correction was found to be important. The approximate method proved to be reliable for thin samples in cases where the cross section for inelastic scattering is small. The effect of the molecular structure of the material on the multiply scattered intensity was demonstrated in the case of liquid sulfur and found to be meaningful at small scattering angles. The correction method was applied to the radial atomic density function (RDF) analysis of water and sulfur. The correction improved the behaviour of the reduced interference function but its effect on the RDF was small in both cases.
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    Transmission electron microscope studies of phase transitions in single crystals and ceramics of ferroelectric Pb(Sc1/2Ta1/2)O3 (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 43-54 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An account is given of transmission electron microscope investigations of the phase transitions in single crystals and ceramics of the complex perovskite structured ferroelectric `relaxor' compound Pb(Sc1/2Ta1/2)O3. The crystal symmetries pertaining to both the non-polar paraelectric (PE) and polar ferroelectric (FE) states have been studied by the technique of convergent-beam electron diffraction. A new phase transition has been discovered in the temperature range for which the FE and PE states coexist. The new phase transition is interpreted as the creation of a modulated antiferroelectric state, and this is viewed as marking a departure from relaxor behaviour towards more `normal' ferroelectric behaviour.
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    High-resolution electron microscopic study on long-period superstructures with 6H stacking sequence in Au3Cd alloys (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 55-62 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Atomic arrangements of long-period superstructures in Au–24.5at.%Cd alloy with the basic h.c.p. structure have been investigated by high-resolution electron microscopy. The alloy shows one-dimensional or two-dimensional long-period superstructures in the close-packed plane with a 6H stacking sequence, depending on heat treatments. It is shown that the two-dimensional incommensurate superstructure with a period larger than 9a0 is composed of domains of the hexagonal commensurate structure (M = 9) separated by the antiphase-boundary zone in which 33/2a0 × 2a0 × 3c0 orthorhombic structure is formed (a0, c0 being the lattice parameters of the h.c.p. structure). Microstructures of the alloy annealed at 620 K with the one-dimensional long-period superstructure and of the alloy quenched from 770 K showing diffuse scattering have also been investigated by high-resolution electron microscopy.
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    Closed-form expressions for Fourier–Bessel transform of Slater-type functions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 71-73 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Integrals of the type G_{N.k}(S,Z) = \int^{\infty}_{0}r^N{\rm exp}(- Zr)j_k(Sr){\rm d}r for k ≤ N − 1 have been directly evaluated and the closed-form expressions are given.
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    The properties of anisotropic small-angle scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 79-81 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that the cross section of small-angle neutron scattering (SANS) on an anisotropic system of point scatterers is determined by a symmetric tensor (R). The mean square radius of gyration of the system is the trace of R. A simple method is proposed for experimental determination of the tensor R by small-angle measurements with rotation of a sample.
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    Linear least-squares adjustment of UB matrix elements and the prediction of reflection positions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 111-114 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is presented for the linear least-squares refinement of small changes in the UB matrix elements and diffractometer offsets in single-crystal diffractometer experiments. It thus affords a rapid method for calculating the consequent changes in the positions of the centres of Bragg reflections.
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    Time modulation of small-angle neutron scattering in the longitudinally vibrating double-crystal system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 70-71 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of two longitudinally vibrating perfect crystals is suggested for small-angle neutron scattering experiments.
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    A versatile new cryostat for obtaining X-ray diffuse intensity data from thin flat single crystals (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 77-77 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Approximation of pole figures for the determination of crystal orientation in polymeric solids (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 88-93 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The approximation of experimentally measured angular intensity distributions of X-rays diffracted by oriented polycrystalline specimens is suggested as a method for the determination of orientation distribution characteristics for uniaxially oriented polymeric fibres. A non-linear optimization program based on a Hook–Jeeves algorithm is elaborated and incorporated into the method. As an example, the interpretation of the data from polyethylene specimens having various degrees of orientation is given. An important application of the method is the analysis of distributions (pole figures) using a superposition of two identical or similar functions with different parameters.
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    A HREM study of nonbasal twinning and superlattices in ilmenite (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 82-87 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microstructures of natural ilmenite found in Panzhihua district, China, were examined by high-resolution electron microscopy (HREM). The [{\bar 1}2{\bar 1}0] structural images showed clearly the (10{\bar 1}1) nonbasal twinning which seems to be coincident with the [{\bar 1}012] rotation twinning. The superlattices with periodicities of 16.8 and 12.6 Å, respectively, as well as the unit-cell twinning related to the ordering of (10{\bar 1}1) multiple twinnings were observed. The superlattice resulting from the ordering arrangement of (10{\bar 1}1) stacking faults related to the slip systems suggested by Heuer [Philos, Mag. (1966), 13, 379–893] were also detected. Possible genetic aspects are considered.
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    An evaluation of selected density-modification methods for protein-structure determination (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 115-131 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effectiveness of density-modification methods in reducing phase errors has been quantitatively analyzed under conditions in which the source and magnitude of phase error could be defined. Progress was gauged by monitoring both the phase errors and electron density. Changes in electron density were monitored in and around the protein density and in the solvent density. The results of this analysis suggest that the improvement possible is more dependent upon the magnitude than on the source of phase error, and that the methods are most effective when the initial phase error is relatively small. As the magnitude of error increases, the improvement gained decreases, and in some cases noise is introduced by the procedure(s).
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    FIT, a computer program for decomposition of powder diffraction patterns and profile analysis of pair correlation functions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 138-140 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: FIT is an interactive computer program for fitting analytical models to powder diffraction patterns and to pair correlation functions. FIT has been written in Turbo C and runs on IBM XT/AT or compatible personal computers.
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    PLOTQ – a computer program for displaying electron densities and related functions in two and three dimensions (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 143-144 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Auto-indexing of oscillation images (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 253-257 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is presented which indexes spots recorded on single oscillation images without any a priori knowledge of cell parameters. The strategy is similar to that used in four-circle diffractometry and the method works in a fully automatic manner. It is applicable to multiple oscillation images or multiple stills. A complementary method is also described to obtain orientation angles for the case where cell parameters have already been determined.
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    Study of ferroelastic domains in HTMA crystals at the ferroelectric–ferroelastic transition (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 277-281 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The ferroelectric ferroelastic phase transitions of tetramethylammonium tetrachlorozincate (HTMA) were observed by standard X-ray topography and by synchrotron topography. Observation of the phase boundary is possible in the latter case. The different kinds of domain walls observed in the ferroelastic phase cast doubts on the commonly assumed symmetry group of this phase.
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    An automated system for micro-batch protein crystallization and screening (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 297-302 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An automatic sample dispenser has been constructed to aid with protein crystallization trials. This dispenser contains a bank of Hamilton syringes driven by stepper motors under computer control which is used to set up small samples (2 μl or less) for batch crystallization. Software has been written to create a series of trials which form a two-dimensional array of crystallization conditions. A specially designed fluoropolymer multibore microtip allows the very small volumes to be mixed and dispensed with great accuracy.
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    Neutron topography as a tool for studying reactive organic crystals: a feasibility study (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 186-198 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The feasibility of using neutron topography as a non-destructive imaging technique for the study of X-ray sensitive organic single crystals, with a view to applying it to the study of reactivity in such crystals, has been tested. Crystals studied range from relatively X-ray insensitive protonated and deuterated pyrene crystals to relatively highly X-ray sensitive 2,4-hexadiynylene bis(p-toluenesulfonate) (PTS) monomer crystals. The latter crystals are readily polymerized in an X-ray beam. Results indicate that neutron topographic imaging provides little advantage over X-ray topography for either the X-ray insensitive or X-ray sensitive crystals studied here. It was concluded that this is mainly due to limitations in spatial resolution attributed to geometric effects inherent to the technique. However, for X-ray sensitive crystals, neutron topography can provide useful information, in a non-destructive way, in the form of rocking-curve data, and as such can be regarded as a useful `ally' technique to the analogous X-ray techniques. It is expected that in the case of extreme X-ray sensitivity, provided geometric losses can be minimized, neutron topography may be the only technique capable of non-destructively revealing bulk defect structures and strain distributions.
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    Enhancement in resolution and lack of radiation damage in a rapidly frozen lysozyme crystal subjected to high-intensity synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 215-218 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray data have been collected from a monoclinic hen egg-white lysozyme (HEWL) crystal, rapidly frozen at 120 K on the end of a glass fiber, using high-intensity synchrotron X-radiation. A comparison of oscillation photographs taken at the beginning and end of data collection shows no evidence of radiation damage even though the crystal was exposed in the synchrotron beam for 8̃ h. Not only are the low-resolution data unaffected by radiation damage but the high-resolution data remain unaffected as well. There is also a marked improvement in the resolution of the diffraction pattern of the rapidly frozen crystal when compared to a similarly sized crystal irradiated in a capillary tube at room temperature.
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    The physics of quasicrystals edited by P. J. Steinhardt and S. Ostlund (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 224-224 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Reduction of parasitic scattering in small-angle X-ray scattering by a three-pinhole collimating system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 241-245 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A series of experiments have been undertaken on the Oak Ridge National Laboratory (ORNL) 10 m small-angle X-ray scattering (SAXS) camera to provide quantitative data on the level of background (parasitic) scattering generated by different types of bevelled collimating slits. The addition of a third (guard) slit, positioned close to the sample, resulted in a reduction of over an order of magnitude in the parasitic background generated by the best two-slit combination of collimating slits. This made it possible to reduce the size of the beamstop, permitting useful data to be collected down to a value of the scattering vector Q = 4πλ−1sinθ ∼ 3 × 10−3 Å−1, where λ is the wavelength, and 2θ is the angle of scatter. This permits the resolution of distances d ̃2π/Q up to 2000 Å.
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    High-pressure single-crystal study on AlPO4 with synchrotron radiation (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 397-400 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A single-crystal study on AlPO4 was performed at 2.90 (7) GPa with synchrotron radiation using a diamond-anvil cell with a beryllium gasket. For the data collection the radiation wavelength of only 0.54 Å, was chosen to minimize the absorption of X-rays in the pressure cell. The diffracted intensity was high enough to measure even weak reflections with sufficient counting statistics. The refined structural parameters are in good agreement with those determined from data collected with a conventional X-ray tube.
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    Structural study of Cd(S,Se) doped glasses. High-resolution transmission electron microscopy (HRTEM) assisted by image processing (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 418-423 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-resolution transmission electron microscopy (HRTEM) was used for examining Cd(S,Se) nanocrystals grown in silicate glasses commercially available as optical filters. The lattice images of the nanocrystals were numerated and submitted to filtering through Fourier transformation in order to sweep off the background signal originating mainly from glass. Optical filters from several firms were examined. The nanocrystals have been identified with Cd(S,Se) compounds crystallized in the wurzite structure, as in bulk material. The lattice images indicate crystallites having the shape of hexagonal prisms a little elongated along the c axis. The distribution of grain size differs according to the filter: the smallest size being about 1.5 nm (threshold for detection), the largest size varies from 7 to 10 nm, the average size sa, from 3–4 to 5–6 nm and the characteristic size sc from 5–6 to 7–8 nm (sc is the size of grains occupying the main part of the crystallized volume).
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    Silicon photodiode detector for small-angle X-ray scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 430-432 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A photodiode X-ray detector was built to measure small-angle X-ray scattering (SAXS) at a synchrotron-radiation source in conjunction with a double-crystal diffractometer SAXS camera at photon energies between 5 and 11 keV. The photodiode detector response in this energy range is linear at photon counting rates up to 1012 photons s−1 and thus it was not necessary to attenuate the monochromatic X-ray beam with calibrated foils. SAXS data taken with a scintillation counter and the photodiode detector are compared, demonstrating marked improvement in counting statistics, rate of data acquisition and signal-to-noise ratio.
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    Sub-nanosecond X-ray powder diffraction (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 441-443 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The X-rays emitted from a laser-produced plasma have been used to obtain powder diffraction patterns with exposures of less than a nanosecond. The X-rays were produced by focusing approximately 50 J of 0.53 μm laser light in a 600 ps (FWHM) pulse to a tight (1̃00 μm diameter) spot on a solid titanium target. The spectral brightness of the resonance line of the helium-like titanium thus produced was sufficient to record diffraction from LiF powder in a single exposure using the Seemann–Bohlin geometry. These results indicate that time-resolved measurements of the lattice parameters of polycrystalline materials can be made with sub-nanosecond temporal resolution.
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    A two-circle powder diffractometer for synchrotron radiation with a closed loop encoder feedback system (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 292-296 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A high-angular-resolution two-circle powder diffractometer equipped with long diffracted-beam collimators has been built at Daresbury Laboratory. The diffractometer has encoders mounted directly on the 2θ and ω axes. These give a nominal angular resolution of 0.1 and 1.0 mdeg respectively. Repeated scans of single powder peaks have demonstrated a reproducibility of 0.1 mdeg 2θ. Measurements on five independent peaks of tungsten give a self consistency of 1(1) × 10−5 Å. An example data set from synthetic olivine Mg2SiO4 has been refined using the Rietveld method and the results compare very well with single-crystal structure refinements.
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    Analytical treatment of the resolution function for small-angle scattering (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 321-333 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analytical expression for the resolution function for small-angle scattering in pinhole geometry are derived. The contributions to the resolution function due to wavelength spread, finite collimation and detector resolution are determined separately using Gaussian functions to approximate the contributions. A general resolution function is derived which is the result of the combined effect of the three contributions. An azimuthal-integrated resolution function, which can be applied to scattering from a material with a circular symmetric scattering cross section, is calculated. This resolution function contains in addition a contribution from the averaging procedure itself. The analytical results are compared with the results of computer simulations. The comparison shows that Gaussian functions give a good description of the resolution function and that the widths agree with those calculated by the analytical expressions. The resolution function is applied in the analysis of two experimental examples: neutron scattering from latex particles [Wignall, Christen & Ramakrishnan (1988). J. Appl. Cryst. 21, 438–451] and neutron scattering from lamellar structures of bilayer lipid membranes (Mortensen, Pfeiffer, Sackmann & Knoll, unpublished). The analytical expressions for the resolution function allow a least-squares analysis to be performed and excellent agreement between experimental and theoretical scattering patterns are obtained.
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    A convenient translation-function parameterization (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 341-343 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A novel parameterization is given for one type of single-symmetry-element translation function, the Q functions of Tollin [Acta Cryst. (1966), 21, 613–614]. This parameterization enables the straightforward computation of these for any symmetry element. A computationally convenient form of the Q-function expression is given. Examples of Q for a selection of symmetry elements, illustrating some of the simplifications of the general form.
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    Crystallographers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 349-350 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    X-ray diffuse scattering of a decomposing hexagonal alloy (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 458-461 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A new type of X-ray diffuse scattering has been found in the early stages of decomposition of the hexagonal phase of Mn–44at.% Al. The diffuse scattering is observed mainly within the basal plane of the reciprocal lattice and differs for the 10{\bar 1}l and 11{\bar 2}l points. Theoretical calculations of the X-ray diffuse scattering according to the kinematic scattering theory have been performed for the elastically isotropic and anisotropic cases and for precipitates of various forms and orientations with and without a depleted layer surrounding them. In the latter case, a zero-intensity region near the reciprocal-lattice points occurs. There are cases of good agreement between the experimental results and calculations for the precipitates with a depleted layer.
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    Array-type universal profile function for powder pattern fitting (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 485-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An array-type universal profile function for powder-pattern fitting is described. It is defined as an array of unknown parameters representing the profile heights at discrete angular steps. The unknown parameters are determined during least-squares fitting together with the integrated intensity, the peak position, the peak width and background parameters. The function has been applied to profile fitting in a small 20 range, and has better R-factors than the pseudo-Voigt and Pearson VII functions. This new function has some important advantages: it can model any complex profile shape, which would be difficult to describe by a smoothly varying analytical-type function; it generally gives a better fit and thus more precise and accurate analysis than currently used analytical-type functions; and it can be applied to the data of all radiation sources including conventional X-rays, synchrotron radiation and time-of-flight and fixed-wavelength neutrons without changing the mathematical form. The optimized use of the function and the accuracy of deduced parameters are also discussed.
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    Automatic evaluation of general spot profiles in oscillation photography (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 549-553 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: An algorithm to determine the exact profiles of digitized spots having arbitrary shapes and sizes is described. It does not require any prior knowledge of crystallographic parameters and can be applied to the digitized data set of any random distribution of arbitrarily shaped peaks of finite size having an average intensity significantly higher than a nearly constant background. Application to the case of oscillation photography data from protein crystals is described.
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    Crystallographers (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 559-559 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Absorption contrast effects in the quantitative XRD analysis of powders by full multiphase profile refinement (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 14-17 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: It is shown that quantitative X-ray powder diffraction analyses using full profile multiphase refinement should include corrections for the Brindley particle absorption contrast effect. This is demonstrated with synthetic mixtures of the highly contrasting phases LiF and Pb(NO3)2 (μ/ρ = 20 and 231 cm−1 for Co Kα). With contrast corrections, the only parameter which needs to be input is an effective particle radius R for each phase. For mixtures of LiF and Pb(NO3)2 over the whole composition range, quantification is achieved, under the present specimen preparation method, with an effective particle radius of 51 μm for both phases, giving analyses correct to within 1 percentage point. Without Brindley corrections, the analysis is grossly in error.
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    The application of synchrotron X-radiation for the study of phase transitions in lipid model membrane systems (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 48-60 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of real-time X-ray diffraction techniques to characterize phase transitions in lipid systems is reviewed. Information such as transition mechanism and thermodynamic order can be correlated with thermodynamic data from scanning calorimetry or densitometry to describe completely the measured thermodynamic quantities in terms of structural phenomena. Dynamic phase information can also be used to produce dynamic phase diagrams which define the parameters for creation of metastable phases in these systems. Examples involving changing lipid and solvent composition are provided to illustrate the utility of the approach.
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    Anomalous small-angle X-ray diffraction of an Nd-Fe multilayer (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 156-163 
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    Notes: The Bragg peak intensities, related to the electronic concentration profile, depend both on atomic concentrations and on specific volumes. Anomalous dispersion, using synchrotron radiation, produces a variation of the scattered intensity, which in principle allows a separation of the two contributions. The kinematic approximation for diffraction of thick multilayers allows an easy evaluation of the ratio of specific volumes, but the entire reflectivity curves and their deformations with photon wavelength can be explained by the interferences between the Kiessig fringes and diffraction maxima in a kinematic approximation. A full optical treatment confirms the previous analysis. Finally, the relaxations occurring during Nd–Fe interdiffusion are too small to be measured in our experimental conditions.
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    Structure determination of LiMoP2O7 from multiphase powder X-ray diffraction data (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 520-525 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The crystal structure of LiMoP2O7 was determined from conventional powder X-ray diffraction at room temperature in the presence of MoP2O7, MoO2 and Mo as impurities. Pattern decomposition was employed to eliminate complex contaminants prior to the Rietveld structure refinement. LiMoP2O7 crystallizes in the space group P21 with Z = 2, a = 4.8987 (3), b = 8.3912 (4), c = 7.0306 (4) Å, β = 109.327 (4)°, V = 272.71 Å3. Final agreement indicators were Rp = 0.0589, Rwp = 0.0772, RF = 0.054 and RI = 0.080. The framework of the structure consists of corner-sharing MoO6 octahedra and P2O7 groups, which form tunnels where the Li cations are located. The results give an example of analyzing a structure from a tetraphasic mixture using pattern decomposition in conjunction with the Rietveld refinement method.
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    XENVIEW - an interactive program to display and analyze electronic area detector data (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 196-196 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    A standardless method of quantitative mineral analysis using X-ray and chemical data (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 197-202 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A complex standardless mineral-analysis method is described which determines both the concentrations and the chemistry of minerals in a batch of m ≤ w + t suitable rock samples, where w and t are the numbers of crystalline and amorphous minerals, respectively. The method is based on data from X-ray diffractometry and the bulk chemistry of the samples. Analytical examples are given. The problem of the accuracy of the analysis is discussed.
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    The influence of laser radiation on X-ray diffraction in ferroelectric crystals with nonlinear optical properties (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 74-76 
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    Notes: The influence of laser radiation (λ = 532, 630 nm) on X-ray diffraction in nonlinear ferroelectric LiNbO3:Fe(0.01–0.02%) and triglycine sulfate (3C2H5NO2.H2O4S) crystals has been studied. The laser radiation was applied to the sample on a four-circle X-ray diffractometer through a flexible optical fiber. The end of the light guide was fixed in a special attachment installed on the goniometer head and allowed the laser beam to be oriented along some chosen direction in a crystal and to maintain this orientation during the whole process of data collection over the reflection sphere. The output power of laser radiation at the end of the light guide was 7 to 10 mW (or about 0.3 W cm−2). The sample irradiation by laser light led to a visible increase of intensity for some reflections (up to 34%). A noticeable difference in the extinction parameters of the samples was found between the sets of reflections measured under normal conditions and those measured under laser irradiation.
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    Effects of tetragonal distortion in thin expitaxic films on electron channeling patterns in scanning electron microscopy (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 102-107 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The elastic strain state in a 25 nm (In,Ga)As epitaxic film deposited on a (001) GaAs substrate includes a Poisson expansion perpendicular to the interface. This creates a tetragonally distorted lattice in the film which shifts high-order Laue-zone (HOLZ) lines in electron channeling patterns (ECP) from the film compared to ECP's from pure GaAs. The line shifts are predictable, thereby allowing measurement of elastic strains parallel and perpendicular to the film/ substrate interface independently. The technique appears to have an accuracy close to 0.2%.
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    Identification of planar defects by etch pits formed on the mantle surface of cylindrical single crystals (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 119-125 
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    Notes: The formation of etch pits directly on the mantle surface of cylindrical single crystals rather than on flat surfaces, as it is usually performed, allows easier and more accurate determination of the crystal orientation. The application of this technique to tungsten single crystals subjected to compression tests at low temperature allows an easy identification of the twinning systems. This technique is well adapted to single crystals subjected to mechanical tests mainly because it does not require the preparation of flat surfaces before or after the test to reveal etch pits. Producing flat surfaces could induce stress within the crystals that in turn could activate slip or twinning mechanisms and would, therefore, give wrong results.
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    Calculation of the refractive indices of molecular crystals (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 171-174 
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    Notes: The anisotropic optical properties of molecular crystals of general symmetry, which are characterized by three different refractive indices and corresponding optical axes, have been calculated by tensorial addition of the bond polarizabilities of all covalent bonds knowing the structure from X-ray diffraction analysis. As an example, refractive indices are given for β-phase fat crystals, viz glyceroltristearate and -tripalmitate, which are very hard to grow. Some of these refractive indices have been measured directly using the immersion method. Furthermore, average refractive indices of such crystals have been calculated by means of the Lorenz–Lorentz equation from the liquid data. As far as comparisons are possible, the theoretical values agree with experiments.
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    SEXIE - a microcomputer program for the calculation of coordination shells and geometries (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 263-263 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Crystal engineering: the design of organic solids by G. R. Desiraju (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 265-265 
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    Focusing double bent crystal (DBC) diffractometer for medium-resolution small-angle neutron scattering (SANS) experiments (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 298-303 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A new modification of a focusing SANS instrument where at least the first crystal is set for diffraction in the asymmetric transmission geometry is presented. Unlike an earlier version which employed both crystals in the symmetric Bragg-case geometry [Kulda & Mikula (1983). J. Appl. Cryst. 16, 498–504], the new modification permits one simultaneously to exploit the effects of natural wavelength focusing and space condensation of the diffracted beam due to asymmetric diffraction. This DBC instrument seems to be suitable for use with beams with a large cross section at the first crystal and for SANS experiments on samples with a small width (few mm).
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    High-symmetry triple junctions in polycrystalline silicon (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 232-238 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Triple junctions in polycrystalline silicon for solar cell applications have been studied by TEM (transmission electron microscopy). The typical characteristic of these junctions is the existence of high-symmetry interfaces, i.e. twins of different order. Whenever the triple junction contains two such interfaces, the intersection axis is a CSL (coincidence site lattice) symmetry axis. In this case the mutual relation of the grain boundaries of the triple junctions is revealed by symmetry rules, since the boundaries are described by symmetry elements of the corresponding CSL which do not belong to the symmetry group of the parent lattice. Therefore, the different variant orientations of these CSL symmetry elements, implied by the symmetry of the lattice, are used for the study of triple junctions. A junction is geometrically characterized by the point-group-symmetry properties. The observations concern symmetrically different triple junctions of the same type of macroscopically stable grain boundaries and faceted and microfaceted interfaces. It is shown that in silicon the thermodynamically favored twins are combined by specific symmetry rules. The results are discussed in accordance with the possible growth mechanisms.
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    Experimental verification of the triple isotopic substitution method in small-angle neutron scattering (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 243-254 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The theoretical predictions of the triple isotopic substitution (TIS) method in small-angle neutron scattering have been confirmed experimentally. A unique advantage of the method, namely the possibility to make part of a complex particle `invisible' in normal (H2O) buffer, is demonstrated. Particle association, the addition of `small' molecules (such as glycerol) or `large' molecules (such as pyruvate kinase) in the solutions under study have been shown not to influence the difference scattering curve obtained. The possibility of extracting normalized interparticle interference functions from the TIS data is discussed. This enables the detection of the presence of aggregates (e.g. dimers) in the solution, even in cases where the molar mass of a particle and/or its concentration are unknown. A simple internal test is suggested which checks whether or not sufficient conditions for the applicability of the method are fulfilled.
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    New Commercial Products (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 264-264 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Experimental strategies in Laue crystallography (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 267-277 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The efficiency of data collection using the Laue technique varies with the wavelength range, the crystal symmetry, the orientation of the crystal in the X-ray beam, the crystal-to-film distance and the acceptance angle of the detector. By optimizing these parameters and by taking advantage of the diffraction symmetry represented by the Laue class, it is often possible to collect a nearly complete data set in one or two exposures. This paper discusses general strategies for data collection and presents results from a computer survey to find optimal crystal orientations for the eleven Laue classes.
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    SANS studies from porous alumina fibres (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 607-615 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The small-angle neutron-scattering pattern from bundles of 3 μm diameter porous alumina fibres has been determined and found to be anisometric. Intense scattering at a narrow divergent angle has been observed perpendicular to the fibre axes, coupled with a lower-intensity scattering over all other angles. The pattern has been analysed by means of sector analysis in order to determine the variation of intensity with modulus of the scattering vector over the range 0.006–0.2 Å−1. A theory has been developed to account for contributions to scattering from, firstly, macroscopic features of the fibres such as alignment distribution and lack of straightness and, secondly, from internal porosity allowing for distributions of size and of orientation with respect to the fibre axis. The parameters of the size distributions have been estimated from the two-dimensional data by directly fitting the scattering equations using a weighted non-negative least-squares principle.
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    Strain field due to a slip band near a grain boundary in an Fe-6at.% Si bicrystal. II. Interpretation of double-crystal topographs (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 324-330 
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    Notes: The lattice distortion due to the head of the slip band at the grain boundary is measured by double-crystal topography. The head of the slip band is approximated by a macrodislocation situated at the grain boundary. To interpret the topographs, the relaxation due to the free surface is included. The Burgers vectors of macrodislocations, i.e. the number of accumulated dislocations, are found.
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    Grazing-incidence X-ray scattering study of the microstructure of tungsten–carbon films (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 638-644 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microstructure of a coating deposited onto a tungsten carbide layer by cathodic sputtering assisted by chemical vapour deposition (CVD) has been analysed by small-angle scattering of X-rays (SAXS) with a conventional laboratory set-up specially adapted for grazing incidence. Anomalous-scattering measurements have also been performed at LURE, the French synchrotron-radiation facility at Orsay with the aim of characterizing the structure of phases present in the coating. SAXS results reveal the existence of very small precipitates; the size of these precipitates determined from the use of the Guinier approximation is about 16 Å, the correlation length deduced from the position of the peak in the small-angle scattering pattern is about 36 Å. The value of the experimental integrated intensity and the variation of the observed intensities with photon energy lead to the conclusion that these nanocrystals are highly enriched in tungsten and embedded in a carbon-based matrix having a weak electronic density. Electron diffraction results support the assumption of the presence of β-WC1 − x, an unstable high-temperature phase. Furthermore, the low electronic density of the matrix is in agreement with face-centred-cubic carbon recently proposed in the literature.
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  • 87
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    Small-angle X-ray scattering study of lamellar microdomains in a block copolymer (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 679-684 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Lamellar microdomains formed in the solvent-cast films of a poly[styrene-block-(ethylene-alt-propylene)] (SEP) diblock polymer were studied by small-angle X-ray scattering (SAXS). The SAXS profiles, displaying a series of peculiar scattering maxima which cannot be ascribed to the higher-order diffraction maxima from a regular lamellar spacing, were analyzed based on a model of the one-dimensional paracrystal with a preferential orientation. The results suggest that these maxima are due to higher-order scattering maxima from single lamellar microdomains. The maxima suggest that the relative standard deviation for the distribution of the polystyrene lamellar size is much smaller than that of the lamellar spacing, giving rise to a situation in which the oscillation of the particle factor with scattering vector h persists up to high h values while that of the lattice factor damps to unity at low h values. The SAXS result was interpreted as being due to a bending distortion of the polystyrene lamella with a smaller thickness and a narrower thickness distribution than those of the poly(ethylene-alt-propylene) lamella. A study by transmission electron microscopy tends to support this result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890012109
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    SAXS investigations of isotactic polypropylene (IPP) fibres mass coloured with organic pigments (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 715-720 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of selected organic pigments on the supermolecular structure of isotactic polypropylene (IPP) fibre has been investigated. For the present work, three organic pigments of different molecular and supermolecular constitution were selected. Undrawn fibres with a minimal technological degree of drawing and fibres at draw ratios of 2, 4 and 5 were examined. The supermolecular structure was explored using small-angle X-ray scattering (SAXS). From the SAXS patterns the one-dimensional intensity function and the correlation function were determined. The parameters characterizing the supermolecular structure of the fibre, i.e. long period and invariant, were assessed. It was found that a lamellar structure develops during fibre formation. A regular lamellar structure is formed irrespective of the presence of pigments. On drawing fibres the high regularity of the lamellar structure decreases. In the drawing process the pigments are at the origin of micropore formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891000808
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  • 89
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    Small-angle neutron scattering study of sodium alkyl sulfate mixed micelles (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 747-752 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Sodium (octyl + decyl) and (octyl + dodecyl) sulfate mixed surfactant solutions containing the two solutes in a 1:1 proportion were studied by small-angle neutron scattering. The measurements were carried out at different concentrations and temperatures. For mathematical reasons it was not possible to determine the composition of mixed micelles through a least-squares fitting procedure, and therefore Clint's theory assuming ideal mixing of the components was used to calculate the monomer concentrations and the composition of micelles. With the calculated composition, two-shell spherical and ellipsoidal shape models were fitted to the experimental scattering curves. Except for the (octyl + dodecyl) sulfate micelles at higher concentrations, the best fit was obtained by a spherical model. The aggregation number in the mixed systems obtained from the fit lies between the aggregation numbers of the two single-component constituent systems, but closer to that of the longer chain and shows strong concentration and temperature dependence. The fractional charge of the mixed micelles was found to be smaller than the fractional charge of the single-component ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891001292
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  • 90
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    First results from a new perfect-crystal small-angle scattering instrument using a bent comb-shaped analyzer crystal (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 562-567 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The use of a bent comb-shaped analyzer crystal in a perfect-crystal SANS instrument makes possible the simultaneous measurement of many points of the rocking curve by means of a one-dimensional position-sensitive detector. This design permits high-resolution measurements with much higher efficiency than standard techniques. Results from our prototype instrument, using seven reflecting plates, are in very good agreement with predictions based on the dynamic theory of neutron diffraction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891005538
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  • 91
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    Microstructure of nanocrystalline TiO2 and Ni at different degrees of compactness (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 603-606 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The change of the microstructure of nanocrystalline TiO2 and Ni as a function of the compaction procedure was measured by small-angle neutron scattering. The scattering cross section is attributed to contributions from crystallites separated by interfacial regions and to voids as well as to correlations in the spatial arrangement of the different structural components. For Ni there is no drastic change in the scattering cross section for the compacted nanocrystalline solid compared with the as-prepared disperse material. For TiO2 the scattering cross section changes substantially during compaction, caused by changes in volume fractions and size distributions of the different components.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891002315
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  • 92
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    Investigation of single-phase glasses using small-angle X-ray scattering techniques (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 616-623 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The study of single-phase glasses by X-ray scattering experiments requires special techniques. Experimental methods and data evaluation procedures aimed at obtaining reliable scattering data in the range of small and intermediate scattering angles are described. These techniques have been applied to the study of the intermediate-range order of silica and phosphate glasses. For commercial silica glasses and for phosphate glasses, the zero-angle scattering was found to be a very suitable parameter to quantify the optical homogeneity. The zero-angle scattering of alkaline-earth metaphosphate glasses was analyzed in terms of the formalism of Bhatia & Thornton [Phys. Rev. B. (1970), 2, 3004–3012]. From the results, conclusions were drawn about the chemical short-range order. In magnesium phosphate glasses, the presence of small clusters of about 1 nm diameter was established.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891000456
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  • 93
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    Investigation of the interface between polymers: a comparison of scattering and reflectivity techniques (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 651-658 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: With the techniques of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) the interfacial region between polymers forming a two-phase structure can be investigated. Various approaches are possible including the classical Porod analysis as well as the Fourier transform, sandwich or contrast-matching techniques. Their application for the determination of the interface width and profile between polymer phases is discussed. As an alternative method X-ray and neutron reflectometry from polymer layer systems has recently been introduced. It allows an accurate determination of various interfacial parameters provided a flat and smooth interface with sufficient contrast between the materials can be prepared. The techniques are compared and discussed with respect to the information which is obtained on the interfacial region of polymers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891000821
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  • 94
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    SANS and SAXS study of block copolymer/homopolymer mixtures (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 672-678 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The lateral and vertical components of the radius of gyration for a single block copolymer chain and those of a single homopolymer chain in the lamellar microdomain space formed by a mixture of diblock copolymers and homopolymers were investigated by means of small-angle neutron scattering (SANS) and the microdomain structures by small-angle X-ray scattering (SAXS). The homopolymers whose molecular weights are much smaller than that of the corresponding chains of the block copolymers were used so that the homopolymers were uniformly solubilized in the corresponding microdomains. The SANS result suggests that the homopolymer chains in the microdomain space as well as the block copolymer chains are more compressed in the direction parallel to the interface and more stretched in the direction perpendicular to the interface than the corresponding unperturbed polymer chains with the same molecular weight. On increasing the volume fraction of the homopolymers the thickness of the lamellar microdomains increases. The block copolymer chains were found to undergo an isochoric affine deformation on addition of the homopolymers or with the change of the thickness of the lamellar microdomains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890014212
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  • 95
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    Study on interdiffusion of polystyrenes of high molecular weight by SANS (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 665-671 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The interdiffusion coefficient Dint of polystyrenes of different molecular weights has been measured. The small-angle neutron scattering (SANS) intensity from a sandwich-like sample consisting of alternating deuterated and protonated films is determined as a function of time and analysed with respect to Dint. In the symmetrical case both components have the same molecular weight and interdiffusion coefficients may be scaled according to the reptation theory D ̃M−2. The WLF (Williams–Landel–Ferry) temperature behaviour is observed. In the asymmetrical case using low- and high-molecular-weight polystyrenes, the interdiffusion is dominated by the faster-moving species. The fast-mode diffusion theory best describes the result. The influence of a non-zero Flory-Huggins interaction parameter χ between deuterated and non-deuterated material has been taken into account showing a significant slowing down for the high-molecular-weight material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890013024
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  • 96
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    Decay of a shear-induced phase transition on a micellar solution measured by time-dependent small-angle neutron scattering (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 740-746 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Transient small-angle neutron scattering (SANS) experiments on sheared aqueous surfactant solutions of trimethyl(tetradecyl)ammonium salicylate (TTMA-Sal) are reported. A 0.005 M solution without shear shows a weak correlation peak. For steady shear rates above a threshold value of Γ = 50 s−1 the scattering pattern shows an abrupt increase in anisotropy which is related to a shear-induced structure transition. The analysis of the anisotropic pattern reveals the existence of two types of micelle: short rodlike micelles which are weakly aligned and very long rodlike aggregates which are strongly aligned and which are only present for Γ above the threshold value. We report results on transient SANS measurements in which the shear rate was changed stepwise from a value of 400 s−1 to zero. It is found that the smaller micelles are randomized in orientation, whereas the longer ones do not change orientation at all but their concentration vanishes. The number of surfactant molecules bound in the smaller micelles (type I) increases with time, whereas the number of surfactants bound in the larger ones (type II) decreases. The sum of both remains constant. The number of surfactant molecules bound in type II micelles decays exponentially with a half life of T1/2 = 1.7 (1) s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889890011189
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  • 97
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    Small-angle X-ray scattering study of cordierite sol–gel synthesis (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 765-770 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structure of ceramic materials in the size range of a few nanometres to a few tens of nanometres is closely related to the structural features of the precursor. Here the nanostructural development of a cordierite (2MgO–2Al2O3–5SiO2) material is studied by SAXS during its processing by a sol-gel route. Homogeneous alcogels were prepared at 298 K by hydrolysis – condensation of a mixture made of Si(OC2H5)4, sec-Al(OC4H9)3, Mg(NO3)2, water and alcohol. The polymeric nature of the mechanism is evidenced. The final size and internal structure of the particles depend on the quantity of water used for hydrolysis. In the gel state, particles of 7 or 8 nm in size exhibiting a mass fractal structure with D = 1.9 are observed. Xerogels resulting from classical drying were powdered. Firing of pellets leads to porous solids. The small-angle scattered intensity grows strongly and the Porod plot shows a linear behaviour with a slope of −3.5. Sintering to full density is very difficult. Aerogels obtained by supercritical drying consist of primary homogeneous units of about 2 nm in size, attached into volume fractal aggregates (D = 1.8). The aerogels exhibit a dramatically improved sintering ability. Full dense glasses are obtained at temperatures less than 1273 K and fine-grained glass ceramics without any nucleating agent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891001103
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  • 98
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    Atomic accessible and contact surfaces as restraints in the Hendrickson & Konnert refinement program (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 941-946 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer algorithm is presented for calculating and, if required, optimizing the extent of atomic areas in a molecule that are accessible to the solvent or in contact with non-solvent atoms either from the same or from another molecule. The algorithm has been implemented as new restraints in a modified version of the least-squares refinement program of Hendrickson & Konnert [In Computing in Crystallography (1980), edited by R. Diamond, S. Ramaseshan & K. Venkatesan, pp. 1301–1325. Bangalore: Indian Academy of Sciences]. Information on the correctness of atomic interactions in a given configuration can thus be used either as added data during the crystallographic X-ray refinement or, independently, in the analysis and modeling of molecular structures. The algorithm appears well suited for studying the structure and interactions of proteins and nucleic acids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891004168
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    RIBBONS 2.0 (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 958-961 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The program RIBBONS 2.0 allows real-time viewing of solid shaded ribbon models of macromolecules. The primary features of the software are the ability to create a wide variety of styles of ribbon drawings interactively and to toggle between various coloring schemes chosen to reflect assorted geometrical and biochemical properties. Spheres, cylinders, dots, polygons and text are also supported. The auxiliary programs included make RIBBONS 2.0 a powerful tool for visual structural analysis as well as for presentation graphics. The program is currently available only for the Silicon Graphics 4D series of workstations. A port to the Evans & Sutherland ESV workstation employing PEX is under development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891007240
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  • 100
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    Potassium titanyl phosphate, KTiOPO4. I. Experimental investigation of optical gyration, absolute optical chirality and twinning (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 963-967 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The optical gyrations of a domain-free section and of a twinned section of the nonlinear optical crystal KTiOPO4 have been measured using a high-accuracy universal polarimeter. An optical gyration at 6328 Å equivalent to an optical rotation of +22° mm−1 together with a significant circular dichroic contribution was found in the domain-free ({\bar 2}10) section whereas equivalent rotations varying between +14 and −20° mm−1 were found in different regions of the twinned section. The absolute indices of the faces of the samples and the existence of twinning in the second section have been established using X-ray anomalous scattering. The regions of opposite optical chirality in the twinned sample have been shown to correlate with those of opposite structural chirality. The results are used to show that the twinning operation in this KTiOPO4 crystal must be one of the twofold rotations 2[010] or 2[100].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891007239
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