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  • Monkey  (2)
  • intergranular fatigue cracking  (2)
  • A. fistulosum var. caespitosum
  • (Thyroid)
  • 2,3-dihydro-2-hexyl-5-methylfuran-3-one
  • Springer  (4)
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  • 1
    ISSN: 1432-1106
    Keywords: Cerebello-cerebral projection ; Dentate nucleus ; Monkey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stimulation of the cerebellar dentate nucleus in monkeys elicited responses in the frontal association cortex (area 9) on the contralateral side to the stimulation, in addition to those in the motor (area 4) and premotor (area 6) cortices which were reported previously. The responses in the frontal association cortex were characterized by surface positive-deep negative field potentials in the cortex. They contrasted with surface negative-deep positive potentials in the motor and premotor cortices on the same dentate nucleus stimulation. In the rostral part of the premotor cortex (area 6) on the border of area 9, both types of responses were induced and admixed. The relay nucleus of the thalamus was suggested for the dentate-induced responses in the frontal association cortex.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Premovement cortical potential ; Visually initiated movement ; Monkey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary With electrodes implanted chronically on the surface and in the depth of the cortex, field potentials were led from the premotor cortex and forelimb areas of the motor and somatosensory cortices of monkeys performing visually initiated hand movements, and then averaged. It was found that the visually initiated movement was preceded by early (latency about 40 ms after the visual stimulus), surface positive, depth negative potentials in the premotor and forelimb motor cortices on both sides. Later on (at about 120 ms latency), surface negative, depth positive potentials emerged prior to the movement in the motor cortex contralateral to the moving hand. The early responses were interpreted as being induced via deep thalamo-cortical and/or corticocortical projections, while the later responses were via superficial thalamo-cortical projections, according to laminar field potential analyses of cortical evoked potentials made in our previous acute experiments. These potentials were clearly different from the premovement potentials recorded in the respective cortices prior to self-paced hand movements: monkeys performing self-paced hand movements showed slowly increasing, surface negative, depth positive premovement potentials in the premotor cortex and the forelimb motor and somatosensory areas contralateral to the moving hand. It was concluded that the central nervous mechanism preparing the cerebral cortex for visually initiated movements is considerably different from that for self-paced movements, both of which consist of the same wrist extension in lifting a lever.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-2746
    Keywords: intergranular fatigue cracking ; Σ3 twin boundary ; iron chromium alloy ; bicrystal ; elastic imcompatibility
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The effect of a geometrical relationship between a grain boundary (GB) plane and a tensile axis on intergranular fatigue cracking along Σ3(1 1 2) twin boundaries has been investigated in Fe-30%Cr alloy crystals. Fatigue experiments were carried out on the three kinds of the specimens containing the Σ3(1 1 2) twin boundary. It was found that the fatigue cracking behavior was sensitive to the geometry of the GB plane. In a specimen where both the GB plane and a slip vector lying in the GB plane in adjacent grains are inclined to the tensile axis at 45°, the fatigue cracks were nucleated preferentially along the twin boundary at a stress amplitude of 170 MPa. The specimen with the GB plane normal to the tensile axis showed that the fatigue crack was initiated from a slip band formed within a constituent grain at a stress amplitude of 300 MPa. When the GB plane was inclined to the tensile axis but the slip vector lying in the GB plane was normal to the tensile axis, development of additional slips formed perpendicular to the GB plane were observed at a specific site of the GB. Initiation of intergranular fatigue cracks at the site was recognized at a stress amplitude of 250 MPa. It can be suggested that the GB plane normal to the tensile axis provides the highest fatigue performance among them. The difference in the cracking property among these specimens could be understood in terms of the effective Schmid factor derived from elastically incompatible stress.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-2746
    Keywords: intergranular fatigue cracking ; twin boundary ; bicrystal ; copper ; persistent slip band
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The criterion for occurrence of intergranular fatigue cracking in copper has been investigated from the view point of both the grain boundary (GB) character and the cyclic deformation property of constituent grains. The copper bicrystals were prepared to have several orientation relationships close to Σ3(1 1 1) coherent twin (Σ3 vicinal domain) so as to change the GB character rapidly with increasing deviation angles |Δθ| from the Σ3 relation. These bicrystals were shaped to single-edge-notched specimens in which a GB plane was perpendicular to the tensile axis. The fatigue crack propagation tests were carried out in air at room temperature. The specimens having deviation angles |Δθ| less than 3° involved no intergranular fatigue cracking. When the |Δθ| values were ranged from 3° to 5°, the ratio of the intergranular cracking increased. In the specimens having the |Δθ| values more than 9°, the intragranular cracking became predominate again. The increase in the intergranular cracking with increasing deviation angle at the |Δθ| values less than 5° could be understood in terms of the increasing GB susceptibility to the GB damage due to air environment. On the other hand, the intragranular cracking at the |Δθ| values more than 9° could be attributed to the formation of the persistent slip bands in the constituent grains and subsequent crack propagation preferentially along them.
    Type of Medium: Electronic Resource
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