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  • Other Sources  (357)
  • MECHANICAL ENGINEERING  (242)
  • ELECTRONICS AND ELECTRICAL ENGINEERING
  • 1990-1994  (357)
  • 1994  (357)
  • 1
    Publication Date: 2019-08-28
    Description: Wideband bandpass filters employing half-wavelength broadside-coupled microstrip lines suitable for microwave and mm-wave integrated monolithic integrated circuits (MIC and MMIC) are presented. Several filters have been developed at X-band (8 to 12 GHz) with 1 dB insertion loss. Fair agreement between the measured and calculated results has been observed. The analysis of the broadside-coupled microstrip lines used in the filters, based on the quasi-static spectral domain technique, is also described.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Microwave Journal (ISSN 0192-6225); 37; 4; p. 210-225
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  • 2
    Publication Date: 2019-08-28
    Description: A Monte Carlo simulation of double-quantum-well (DQW) devices is presented in view of analyzing the quantum state transfer (QST) effect. Different structures, based on the AlGaAs/GaAs system, were simulated at 77 and 300 K and optimized in terms of electron transfer and device speed. The analysis revealed the dominant role of the impurity scattering for the QST. Different approaches were used for the optimization of QST devices and basic physical limitations were found in the electron transfer between the QWs. The maximum transfer of electrons from a high to a low mobility well was at best 20%. Negative differential resistance is hampered by the almost linear rather than threshold dependent relation of electron transfer on electric field. By optimizing the doping profile the operation frequency limit could be extended to 260 GHz.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Journal of Applied Physics (ISSN 0021-8979); 76; 11; p. 7428-7436
    Format: text
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  • 3
    Publication Date: 2019-08-17
    Description: An electrically conductive, thermally insulating current lead assembly has been developed for cryogenic systems. This lead assembly consists of thick film elements of high temperature superconductive materials deposited onto a low thermal conductivity substrate. The superconductor elements provide current transport but minimize heat transfer. The substrate provides the mechanical durability necessary for cryogenic and other environments.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NAS 1.71:LAR-14964-1-CU
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  • 4
    Publication Date: 2019-08-17
    Description: Measured sound power data from eight different spur, single and double helical gear designs are compared with predictions of transmission error by the Load Distribution Program. The sound power data was taken from the recent Army-funded Advanced Rotorcraft Transmission project. Tests were conducted in the NASA gear noise rig. Results of both test data and transmission error predictions are made for each harmonic of mesh frequency at several operating conditions. In general, the transmission error predictions compare favorably with the measured noise levels.
    Keywords: MECHANICAL ENGINEERING
    Type: AD-A290304 , ARL-TR-493 , E-8954 , NAS 1.15:106647 , NASA-TM-106647 , Joint Propulsion Conference; Jun 27, 1994 - Jun 29, 1994; Indianapolis, IN; United States
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  • 5
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    In:  CASI
    Publication Date: 2019-08-17
    Description: The majority of recent theoretical and experimental reports published in the literature dealing with helical slow-wave structures focus on the dispersion characteristics and their effects due to the finite helix wire thickness and attenuation, dielectric loading, metal loading, and the introduction of plasma. In many papers, an effective dielectric constant is used to take into account helix wire dimensions and conductivity losses, while the propagation constant of the signal and the interaction impedance of the structure are found to depend on the surface resistivity of the helix. Also, various dielectric supporting rods are simulated by one or several uniform cylinders having an effective dielectric constant, while metal vane loading and plasma effects are incorporated in the effective dielectric constant. The papers dealing with coupled cavities and folded or loaded wave guides describe equivalent circuit models, efficiency enhancement, and the prediction of instabilities for these structures. Equivalent circuit models of various structures are found using computer software programs SUPERFISH and TOUCHSTONE. Efficiency enhancement in tubes is achieved through dynamic velocity and phase adjusted tapers using computer techniques. The stability threshold of unwanted antisymmetric and higher order modes is predicted using SOS and MAGIC codes and the dependence of higher order modes on beam conductance, section length, and effective Q of a cavity is shown.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-TM-106639 , E-8943 , NAS 1.15:106639
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  • 6
    Publication Date: 2019-08-17
    Description: A tactile display device utilizes an electrorheological fluid to activate a plurality of tactile dots. A voltage is selectively produced uniformly across an electrorheological fluid flowing between a common ground electrode and a plurality of conductive dot electrodes, thereby producing an increase in the fluid's viscosity to the extent that fluid flow between the two electrodes is restricted. The flow restriction produces a build-up of electrorheological fluid in a corresponding dot actuator chamber. The resulting pressure increase in the chamber displaces an elastic diaphragm fixed to a display surface to form a lump which can be perceived by the reader as one dot in a Braille character cell. A flow regulation system provides a continually pressurized flow system and provides for free flow of the electrorheological fluid through the plurality of dot actuator chambers when they are not activated. The device is adaptable to printed circuit techniques and can simultaneously display tactile dots representative of a full page of Braille characters stored on a medium such as a tape cassette or to display tactile dots representative of non-Braille data appearing on a computer monitor or contained on another data storage medium. In an alternate embodiment, the elastic diaphragm drives a plurality of spring-loaded pins provided with positive stops to maintain consistent displacements of the pins in both their actuated and nonactuated positions.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NAS 1.71:LAR-14860-1
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  • 7
    Publication Date: 2019-08-17
    Description: Several types of periodic vane slow-wave structures were fabricated. The dispersion characteristics were found by theoretical analysis, experimental testing, and computer simulation using the MAFIA code. Computer-generated characteristics agreed to approximately within 2 percent of the experimental characteristics for all structures. The theoretical characteristics, however, deviated increasingly as the width to height ratio became smaller. Interaction impedances were also computed based on the experimental and computer-generated resonance frequency shifts due to the introduction of a perturbing dielectric rod.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-TM-106641 , E-8945 , NAS 1.15:106641
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  • 8
    Publication Date: 2019-08-17
    Description: This paper presents a summary of the transmission diagnostics research work conducted at NASA Lewis Research Center over the last four years. In 1990, the Transmission Health and Usage Monitoring Research Team at NASA Lewis conducted a survey to determine the critical needs of the diagnostics community. Survey results indicated that experimental verification of gear and bearing fault detection methods, improved fault detection in planetary systems, and damage magnitude assessment and prognostics research were all critical to a highly reliable health and usage monitoring system. In response to this, a variety of transmission fault detection methods were applied to experimentally obtained fatigue data. Failure modes of the fatigue data include a variety of gear pitting failures, tooth wear, tooth fracture, and bearing spalling failures. Overall results indicate that, of the gear fault detection techniques, no one method can successfully detect all possible failure modes. The more successful methods need to be integrated into a single more reliable detection technique. A recently developed method, NA4, in addition to being one of the more successful gear fault detection methods, was also found to exhibit damage magnitude estimation capabilities.
    Keywords: MECHANICAL ENGINEERING
    Type: ARL-TR-599 , NASA-TM-106746 , E-9158 , NAS 1.15:106746
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  • 9
    Publication Date: 2019-08-16
    Description: The invention is an apparatus and method for forming woven fabrics through the use of an adjustable reed. The adjustable reed has multiple groups of reed wires that guide the warp yarns. The groups of reed wires move on reed rails parallel to the warp direction. In addition, rail expanders permit the space between the reed wires to be modified and telescoping rods attached to the rail sliders can be turned to permit the reed wires to be skewed to alter the fill yarn angle. These adjustments to the reed permit simultaneous variation of fill yarn angles and fabric widths and allow these variations to be made during fabrication, without the need to halt production.
    Keywords: MECHANICAL ENGINEERING
    Type: NAS 1.71:LAR-15072-1
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  • 10
    Publication Date: 2019-08-16
    Description: Three dimensional stress analysis of spiral bevel gears in mesh using the finite element method is presented. A finite element model is generated by solving equations that identify tooth surface coordinates. Contact is simulated by the automatic generation of nonpenetration constraints. This method is compared to a finite element contact analysis conducted with gap elements.
    Keywords: MECHANICAL ENGINEERING
    Type: AD-A290276 , ARL-TR-478 , E-8947 , NAS 1.15:106643 , NASA-TM-106643 , Joint Propulsion Conference; Jun 27, 1994 - Jun 29, 1994; Indianapolis, IN; United States
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