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At least 811 records · Page 45

Neutral buoyancy methodology for studying satellite servicing EVA crewmember interfaces

Current economic constraints indicate the need for incorporating the satellite servicing philosophy of commonality within the design of spacecraft subsytems. This philosophy is essential for conserving resources including hardware/software development and implementation costs, on-orbit and ground-based manpower, crew training/testing time, and documentation. In addition, spacecraft subsystem commonality may be coupled with standardization of operation procedures, and test and verification techniques for spacecraft design. Several spacecraft have adopted this practice, including Hubble Space Telescope, Space Station Freedom, and the Explorer Platform. As these and other programs continue and if effective crew interfaces and procedures are clearly and consistently defined, crew retraining for similar spacecraft subsystems will lessen, and procurement efforts will diminish. A relatively high fidelity zero-gravity simulation using water immersion is available to establish crew interfaces economically. The flexibility and utility of this space simulation medium for planning and assisting on-orbit operations was exemplified by astronaut evaluations of potential EVA electrical connectors. The testing was conducted at a NASA underwater neutral buoyancy training facility.

Barnby, Mary E.↗

Comparisons of one- and two- interface methods for tunnel wall interference calculation

Tunnel wall interference in two-dimensional subsonic flow can be analytically calculated on the basis of the one- or two-interface method. The application of numerical integration by means of matrix multiplication to both methods has been found to significantly reduce CPU time in on-line operation. An investigation of the sensitivity of these methods to random velocity-measurement disturbances shows the one-interface method to be less sensitive to measurement errors, and therefore to be preferable for practical applications.

Lo, C. F.↗

A direct-interface fusible heat sink for astronaut cooling

Astronaut cooling during extravehicular activity is a critical design issue in developing a portable life support system that meets the requirements of a space station mission. Some the requirements are that the cooling device can be easily regenerable and nonventing during operation. In response to this, a direct-interface, fusible heat sink prototpye with freezable quick-disconnects was developed. A proof-of-concept prototype was constructed and tested that consists of an elastic container filled with normal tap water and having two quick-disconnects embedded in a wall. These quick-disconnects are designed so that they may be frozen with the ice and yet still be joined to the cooling system, allowing an immediate flow path. The inherent difficulties in a direct-interface heat sink have been overcome, i.e., (1) establishing an initial flow path; (2) avoiding low-flow freeze-up; and (3) achieving adequate heat-transfer rates at the end of the melting process. The requirements, design, fabrication, and testing are discussed.

Lomax, Curtis↗

Micro Channel/Multibus-II Interface Circuit

Micro Channel/Multibus-II interface circuit provides electrical interconnections enabling communications between Micro Channels of IBM Personal System/2 computers and IEEE 1296 standard Multibus-II parallel system bus (iPSB). Made mostly of commercially available parts, interface enables independent Micro Channels to communicate over iPSB without modification.

D'Ambrose, John J.↗

Reduction of thermal stresses in continuous fiber reinforced metal matrix composites with interface layers

The potential of using an interface layer to reduce thermal stresses in the matrix of composites with a mismatch in coefficients of thermal expansion of fiber and matrix was investigated. It was found that compliant layers, with properties of readily available materials, do not have the potential to reduce thermal stresses significantly. However, interface layers with high coefficient of thermal expansion can compensate for the mismatch and reduce thermal stresses in the matrix significantly.

Jansson, S.↗

Numerical study of supersonic combustors by multi-block grids with mismatched interfaces

A three dimensional, finite rate chemistry, Navier-Stokes code was extended to a multi-block code with mismatched interface for practical calculations of supersonic combustors. To ensure global conservation, a conservative algorithm was used for the treatment of mismatched interfaces. The extended code was checked against one test case, i.e., a generic supersonic combustor with transverse fuel injection, examining solution accuracy, convergence, and local mass flux error. After testing, the code was used to simulate the chemically reacting flow fields in a scramjet combustor with parallel fuel injectors (unswept and swept ramps). Computational results were compared with experimental shadowgraph and pressure measurements. Fuel-air mixing characteristics of the unswept and swept ramps were compared and investigated.

Moon, Young J.↗

Design and implementation of interface units for high speed fiber optics local area networks and broadband integrated services digital networks

The design and implementation of interface units for high speed Fiber Optic Local Area Networks and Broadband Integrated Services Digital Networks are discussed. During the last years, a number of network adapters that are designed to support high speed communications have emerged. This approach to the design of a high speed network interface unit was to implement package processing functions in hardware, using VLSI technology. The VLSI hardware implementation of a buffer management unit, which is required in such architectures, is described.

Tobagi, Fouad A.↗

Formal specification of human-computer interfaces

A high-level formal specification of a human computer interface is described. Previous work is reviewed and the ASLAN specification language is described. Top-level specifications written in ASLAN for a library and a multiwindow interface are discussed.

Auernheimer, Brent↗

Guidance for human interface with artificial intelligence systems

The beginning of a research effort to collect and integrate existing research findings about how to combine computer power and people is discussed, including problems and pitfalls as well as desirable features. The goal of the research is to develop guidance for the design of human interfaces with intelligent systems. Fault management tasks in NASA domains are the focus of the investigation. Research is being conducted to support the development of guidance for designers that will enable them to make human interface considerations into account during the creation of intelligent systems.

Potter, Scott S.↗

Considerations for human-machine interfaces in tele-operations

Numerous factors impact on the efficiency of tele-operative manipulative work. Generally, these are related to the physical environment of the tele-operator and how he interfaces with robotic control consoles. The capabilities of the operator can be influenced by considerations such as temperature, eye strain, body fatigue, and boredom created by repetitive work tasks. In addition, the successful combination of man and machine will, in part, be determined by the configuration of the visual and physical interfaces available to the teleoperator. The design and operation of system components such as full-scale and mini-master manipulator controllers, servo joysticks, and video monitors will have a direct impact on operational efficiency. As a result, the local environment and the interaction of the operator with the robotic control console have a substantial effect on mission productivity.

Newport, Curt↗

Diverse applications of advanced man-telerobot interfaces

Advancements in man-machine interfaces and control technologies used in space telerobotics and teleoperators have potential application wherever human operators need to manipulate multi-dimensional spatial relationships. Bilateral six degree-of-freedom position and force cues exchanged between the user and a complex system can broaden and improve the effectiveness of several diverse man-machine interfaces.

Mcaffee, Douglas A.↗

Cooperative processing user interfaces for AdaNET

A cooperative processing user interface (CUI) system shares the task of graphical display generation and presentation between the user's computer and a remote host. The communications link between the two computers is typically a modem or Ethernet. The two main purposes of a CUI are reduction of the amount of data transmitted between user and host machines, and provision of a graphical user interface system to make the system easier to use.

Gutzmann, Kurt M.↗

A rigid line inclusion at a bimaterial interface

A solution is presented for the plane elastostatics problem of a rigid line inclusion at a bimaterial interface. Explicit expressions are derived for the complex potentials. The complex stress intensity factors at the tip of the rigid line are compared with those for the corresponding crack problem. It is found that the nature of the singularities differ. Furthermore, unlike the crack problem, the singularity for the rigid line inclusion depends on the stresses parallel to the interface.

Ballarini, Roberto↗

Sulfur at nickel-alumina interfaces - Molecular orbital theory

Previous studies on Al-Ni alloys containing sulfur as an impurity suggest that, when S is in the interface between a metal and an oxide scale, it weakens the chemical bonding between them. This paper investigates factors responsible for this effect, using a molecular orbital theory to predict sulfur structures and electronic properties on the Ni-Al2O3 interface. It is shown that, in absence of S, the basal plane of Al2O3 will bind strongly through the Al(3+) cation surface to Ni (111). When segregated S impurity is present on the Ni surface, there are too few interfacial AlS bonds to effect good adhesion, leading to an inhibition of the oxide scale adhesion in NiCrAl alloys.

Hong, S. Y.↗

Numerical study of supersonic combustors by multi-block grids with mismatched interfaces

A three-dimensional, finite-rate chemistry, Navier-Stokes code has been extended to a multi-block with mismatched interface code for practical calculations of supersonic combustors. To ensure global conservation, a conservative algorithm was used for the treatment of mismatched interfaces. The extended code was checked against one test case, i.e., a generic supersonic combustor with transverse fuel injection, examining solution accuracy, convergence, and local mass flux error. After testing, the code was used to simulate the chemically reacting flow fields in a scramjet combustor with parallel fuel injectors (unswept and swept ramps). Computational results were compared with experimental shadowgraph and pressure measurements. Fuel-air mixing characteristics of the unswept and swept ramps were compared and investigated.

Moon, Young J.↗

Equilibrium structure of the plasma sheet boundary layer-lobe interface

Observations are presented which show that plasma parameters vary on a scale length smaller than the ion gyroradius at the interface between the plasma sheet boundary layer and the lobe. The Vlasov equation is used to investigate the properties of such a boundary layer. The existence, at the interface, of a density gradient whose scale length is smaller than the ion gyroradius implies that an electrostatic potential is established in order to maintain quasi-neutrality. Strongly sheared (scale lengths smaller than the ion gyroradius) perpendicular and parallel (to the ambient magnetic field) electron flows develop whose peak velocities are on the order of the electron thermal speed and which carry a net current. The free energy of the sheared flows can give rise to a broadband spectrum of electrostatic instabilities starting near the electron plasma frequency and extending below the lower hybrid frequency.

Romero, H.↗

The effect of an electric field on the morphological stability of the crystal-melt interface of a binary alloy. III - Weakly nonlinear theory

The effect of a constant electric current on the crystal-melt interface morphology during directional solidification at constant velocity of a binary alloy is considered. A linear temperature field is assumed, and thermoelectric effects and Joule heating are neglected; electromigration and differing electrical conductivities of crystal and melt are taken into account. A two-dimensional weakly nonlinear analysis is carried out to third order in the interface amplitude, resulting in a cubic amplitude equation that describes whether the bifurcation from the planar state is supercritical or subcritical. For wavelengths corresponding to the most dangerous mode of linear theory, the demarcation between supercritical and subcritical behavior is calculated as a function of processing conditions and material parameters. The bifurcation behavior is a sensitive function of the magnitude and direction of the electric current and of the electrical conductivity ratio.

Wheeler, A. A.↗

Directional solidification of a planar interface in the presence of a time-dependent electric current

Directional solidification of pure materials and binary alloys with a planar crystal-metal interface in the presence of a time-dependent electric current is considered. For a variety of time-dependent currents, the temperature fields and the interface velocity as functions of time are presented for indium antimonide and bismuth and for the binary alloys germanium-gallium and tin-bismuth. For the alloys, the solid composition is calculated as a function of position. Quantitative predictions are made of the effect of an electrical pulse on the solute distribution in the solidified material.

Brush, L. N.↗