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  • 1
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    Efficient Power Amplifier for Motor Control (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Pulse-width-modulated amplifier supplies high current as efficiently as low current needed for starting and running motor. Key to efficiency of motor-control amplifier is V-channel metal-oxide/semiconductor transistor Q1. Device has low saturation resistance. However, has large gate input capacitance and small margin between its turn-on voltage and maximum allowable gate-to-source voltage. Circuits for output stages overcome limitations of VMOS device.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: GSC-12807 , NASA Tech Briefs (ISSN 0145-319X); 9; 3; P. 40
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Histological and compositional responses of bone to immobilization and other experimental conditions (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Histological techniques were utilized for evaluating progressive changes in tibial compact bone in adult male monkeys during chronic studies of immobilization-associated osteopenia. The animals were restrained in a semirecumbent position which reduces normally occurring stresses in the lower extremities and results in bone mass loss. The longest immobilization studies were of seven months duration. Losses of haversian bone tended to occur predominatly in the proximal tibia and were characterized by increased activation with excessive depth of penetration of osteoclastic activity. There was no apparent regulation of the size and orientation of resorption cavities. Rapid bone loss seen during 10 weeks of immobilization appeared to be due to unrestrained osteoclastic activity without controls and regulation which are characteristic of adaptive systems. The general pattern of loss persisted throughout 7 months of immobilization. Clear cut evidence of a formation phase in haversian bone was seen only after two months of reambulation.
    Keywords: AEROSPACE MEDICINE
    Type: NASA-CR-175837 , NAS 1.26:175837
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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