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  • Other Sources  (191)
  • FLUID MECHANICS AND HEAT TRANSFER  (82)
  • STRUCTURAL MECHANICS  (59)
  • COMMUNICATIONS AND RADAR  (50)
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  • Chemical Engineering
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  • SPACE SCIENCES
  • 1990-1994  (191)
  • 1980-1984
  • 1991  (191)
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  • 1990-1994  (191)
  • 1980-1984
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  • 1
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    Electromagnetic scattering from arbitrary shaped conducting bodies coated with lossy materials of arbitrary thickness (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A simple and efficient numerical technique is presented to solve the electromagnetic scattering problem of coated conducting bodies of arbitrary shape. The surface equivalence principle is used to formulate the problem in terms of a set of coupled integral equations involving equivalent electric and magnetic surface currents which represent boundary fields. The conducting structures and the dielectric materials are modeled by planar triangular patches, and the method of moments is used to solve the integral equations. Numerical results for scattering cross sections are given for various structures and compared with other available data. These results are proved accurate by a number of representative examples.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 39; 627-631
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  • 2
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    On estimating the phase of a periodic waveform in additive Gaussian noise, part 3 (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Motivated by advances in signal processing technology that support more complex algorithms, researchers have taken a new look at the problem of estimating the phase and other parameters of a nearly periodic waveform in additive Gaussian noise, based on observation during a given time interval. Parts 1 and 2 are very briefly reviewed. In part 3, the actual performances of some of the highly nonlinear estimation algorithms of parts 1 and 2 are evaluated by numerical simulation using Monte Carlo techniques.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 157-160
    Format: application/pdf
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  • 3
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    Recent advances in coding theory for near error-free communications (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Channel and source coding theories are discussed. The following subject areas are covered: large constraint length convolutional codes (the Galileo code); decoder design (the big Viterbi decoder); Voyager's and Galileo's data compression scheme; current research in data compression for images; neural networks for soft decoding; neural networks for source decoding; finite-state codes; and fractals for data compression.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA, Washington, Technology 2000, Volume 2; p 229-241
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  • 4
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    Experiences in porting NASTRAN (R) to non-traditional platforms (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The 1990 UNIX version of NASTRAN was ported to two new platforms that are not supported by COSMIC: the Sun SPARC workstation and the Apple Macintosh using the A/UX version of UNIX. The experiences of the authers in porting NASTRAN is summarized here. Suggestions for users who might attempt similar ports are given.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Software Management and Information Center, Nineteenth NASTRAN (R) Users' Colloquium; p 14-21
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  • 5
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    Direct sequence spread spectrum CDMA in shared spectrum applications (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Personal Communication Network (PCN) is an entirely wireless communication system with the capability of assessing the wired telephone system to reach anyone processing only a wired telephone. It is expected to compete with the existing mobile cellular system which connects directly to the wired telephone system. While many PCN systems employ TDMA technology, the PCN system described here uses Broadband CDMA (BCDMA(sup SM)) which is capable of sharing the spectrum with other users and which is extremely resistant to fading caused by multipath.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, Proceedings of the Workshop on Advanced Network and Technology Concepts for Mobile, Micro, and Personal Communications; p 219-226
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  • 6
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    Design and fabrication of an erectable truss for precision segmented reflector application (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 28; 251-257
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  • 7
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    Graphite Fiber/Copper Matrix Composites for Space Power Heat Pipe Fin Applications (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: High specific thermal conductivity (thermal conductivity divided by density) is a major design criterion for minimizing system mass for space power systems. For nuclear source power systems, graphite fiber reinforced copper matrix (Gr/Cu) composites offer good potential as a radiator fin material operating at service temperatures above 500 K. Specific thermal conductivity in the longitudinal direction is better than beryllium and almost twice that of copper. The high specific thermal conductivity of Gr/Cu offers the potential of reducing radiator mass by as much as 30 percent. Gr/Cu composites also offer the designer a range of available properties for various missions and applications. The properties of Gr/Cu are highly anisotropic. Longitudinal elastic modulus is comparable to beryllium and about three times that of copper. Thermal expansion in the longitudinal direction is near zero, while it exceeds that of copper in the transverse direction.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: E-5697 , In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 313-319.
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  • 8
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    Synthesis of structural/control systems robust with respect to design variable tolerances (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A methodology is presented for the synthesis of control augmented structures which can be modeled as an assemblage of beam, truss, and nonstructural mass elements augmented by a robust noncollocated direct output feedback control system. The control system is robust in the sense that it can tolerate manufacturing and realization errors. The robust control system is synthesized using a constraint buffering technique in conjunction with the approximation concepts approach to system synthesis. All of the design constraints on the system, including the dynamic stability, are buffered by a nonlinear quantity that is a function of acceptable tolerances on the design variables and the sensitivity of the constraints to changes in these design variables. Numerical results which illustrate the effectiveness of the method presented are given.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA PAPER 91-1156 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Apr 08, 1991 - Apr 10, 1991; Baltimore, MD; United States
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  • 9
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    Dynamical eigenfunction decomposition of turbulent channel flow (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The results of an analysis of low-Reynolds-number turbulent channel flow based on the Karhunen-Loeve (K-L) expansion are presented. The turbulent flow field is generated by a direct numerical simulation of the Navier-Stokes equations at a Reynolds number Re(tau) = 80 (based on the wall shear velocity and channel half-width). The K-L procedure is then applied to determine the eigenvalues and eigenfunctions for this flow. The random coefficients of the K-L expansion are subsequently found by projecting the numerical flow field onto these eigenfunctions. The resulting expansion captures 90 percent of the turbulent energy with significantly fewer modes than the original trigonometric expansion. The eigenfunctions, which appear either as rolls or shearing motions, possess viscous boundary layers at the walls and are much richer in harmonics than the original basis functions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: International Journal for Numerical Methods in Fluids (ISSN 0271-2091); 12; 585-604
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  • 10
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    A general approach for the prediction of localized instability generation in boundary layer flows (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The present approach to the prediction of instability generation that is due to the interaction of freestream disturbances with regions of subscale variations in surface boundary conditions can account for the finite Reynolds number effects, while furnishing a framework for the study of receptivity in compressible flow and in 3D boundary layers. The approach is illustrated for the case of Tollmien-Schlichting wave generation in a Blasius boundary layer, due to the interaction of a freestream acoustic wave with a localized wall inhomogeneity. Results are presented for the generation of viscous and inviscid instabilities in adverse pressure-gradient boundary layers, supersonic boundary layer instabilities, and cross-flow vortex instabilities.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Boundary layer transition and control; Proceedings of the Conference, Univ. of Cambridge, United Kingdom, Apr. 8-12, 1991 (A93-17251 04-34); p. 45.1-45.20.
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