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  • 1
    ISSN: 1432-0630
    Keywords: 68.35 ; 68.55 ; 82.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Epitaxial NiSi2 islands have been grown on Si(111) substrates by the direct reaction of nickel vapour with the silicon substrate in ultra-high vacuum at 400° C. Growth kinetics was shown to depend on the orientation of the islands: A-oriented islands grow about ten times faster than B-oriented ones, with the ratio of the advance rates of the main growth fronts even reaching 30. Applying plan-view transmission electron microscopy and high-resolution electron microscopy of cross sections, a corresponding difference was found in the structure of the NiSi2/Si(111) growth front: Steps at the B-oriented growth front were of three or six interplanar (111) spacings in height, whereas at the A-oriented growth front step-like defects of less than one interplanar (111) spacing in height were observed. These observations are explained by an atomic-scale model of the solid-state reaction, which involves the diffusion of nickel to the interfaces and the nucleation and subsequent lateral propagation of interfacial steps. The difference in the reaction kinetics originates from the presence of kinetic reaction barriers at the NiSi2/Si(111) growth fronts, the barrier at the B-front being higher owing to the lower formation rate of steps of triple atomic height than that of steps of lower height at the A-NiSi2/Si(111) growth front.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1435-1803
    Keywords: ischemia ; reperfusion ; vitamin E ; infarct size ; regionalsystolic shortening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Thirty pigs were randomly assigned to a blind treatment with vitamin E or placebo. Ten animals each received 0.5g d-alpha tocopherol intravenously before ischemia (group 1) or before reperfusion (group 2). Ten control pigs were treated with a lipid emulsion as placebo. The left anterior descending coronary artery was distally ligated for 45 min followed by 3 days of reperfusion. Infarct size was determined as ratio of infarcted (tetrazolium stain) to ischemic myocardium (dye technique). Regional systolic shortening was assessed by sonomicrometry. Myocardial and plasma concentrations of vitamin E were determined by high-performance liquid chromatography. Global hemodynamic parameters and estimated left ventricular oxygen consumption did not differ among the three groups. Intravenous treatment with vitamin E raised the plasma levels of this vitamin from 1 ± 0.3 mg/l (control group) to 21 ± 6 mg/l before ischemia, to 4 ± 2 mg/l before reperfusion and to 2 ± 0.6 mg/l at the end of the experiments in group 1. In group 2, vitamin E plasma levels increased from 1 ± 0.3 mg/l to 24 ± 13 mg/l before reperfusion and to 2 ± 0.6 mg/l after 3 days of reperfusion. At the end of the experiments, myocardial vitamin E concentrations amounted to 4.2 ± 0.7 ng/mg fresh weight (control group), 9.7 ± 2.1 ng/mg (group 1), and to 8.7 ± 1.4 ng/mg (group 2). The increase in vitamin E plasma concentration was not associated with a cardioprotective effect. Infarct sizes of the three groups (group 1: 68 ± 12%, group 2: 66 ± 15%, control group: 69 ± 8%) were almost identical. Furthermore, recovery of systolic shortening was not improved by the acute vitamin E treatment. Mean systolic shortening of the reperfused segment amounted to 4% in the two treatment groups and 3% in the control group after 3 days of reperfusion. These results suggest that an acute increase in vitamin E plasma concentration before ischemia or during the early phase of reperfusion does not protect the ischemic, reperfused porcine heart.
    Type of Medium: Electronic Resource
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