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  • 1995-1999  (2)
  • 1975-1979
  • 1965-1969
  • 1930-1934
  • 1830-1839
  • 1999  (2)
  • 1-butene  (1)
  • Children  (1)
  • acid site concentration
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Catalysis letters 57 (1999), S. 209-215 
    ISSN: 1572-879X
    Keywords: 1-butene ; skeletal isomerization ; mesoporous material ; acid site concentration ; monomolecular reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract On the skeletal isomerization of 1-butene, mesoporous materials with mesopores too large to expect any shape selectivity have been used in order to investigate the effects of the concentration of acid sites on the conversion of 1-butene and the selectivity for isobutene. The concentrations of acid sites can be varied through the control of the Si/Al ratio. The conversion of 1-butene increases with increasing the aluminium content of mesoporous materials, while the selectivity for isobutene decreases. The results of ammonia TPD, IR measurement of 1-butene adsorption, and TG analysis of used catalysts indicate that distant location of activated 1-butene molecules induces the monomolecular reaction over the mesoporous materials with low aluminium content, resulting in high selectivity for skeletal isomerization. On the mesoporous material with high aluminium content, however, the high concentration of activated 1-butene molecules accelerates the multimolecular oligomerization and, thus, reduces the selectivity.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Neuroradiology 41 (1999), S. 512-516 
    ISSN: 1432-1920
    Keywords: Key words Meninges ; Tumours ; Children
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Childhood meningeal tumours are uncommon and mostly meningiomas. We reviewed the histological and radiological findings in meningeal tumours in six children aged 12 years or less (four benign meningiomas, one malignant meningioma and one haemangiopericytoma). Compared to the adult counterpart, childhood meningiomas showed atypical features: cysts, haemorrhage, aggressiveness and unusual location. MRI features varied according to the site of the tumour, histology, haemorrhage, and presence of intra- or peritumoral cysts. Diagnosis of the extra-axial tumour was relatively easy in two patients with meningiomas, one malignant meningioma and one haemangiopericytoma. MRI findings strongly suggested an intra-axial tumour in two patients with benign meningiomas, because of severe adjacent edema. Awareness of the variable findings of childhood meningiomas and similar tumours may help in differentiation from brain tumours.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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