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At least 127 records · Page 7

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NASA NTRS1992

Reflection high-energy electron diffraction study of growth and interface formation of the Ga(1-x)In(x)Sb/InAs strained-layer superlattices

Reflection high-energy electron diffraction (RHEED) during molecular beam epitaxy is used to study the growth and interface formation of the Ga(1-x)In(x)Sb/InAs (x is not greater than 0.4) strained-layer superlattices (SLSs) on GaSb(100) substrates. A number of surface atomic structures were observed in the growth of the SLS: a (1 x 3) phase from the InAs epilayer surface, a (2 x 3) phase, a (2 x 4) phase, and diffuse (1 x 1)-like phases from the InAs epilayer surface. It is suggested that the long-range order quality of the interface of Ga(1-x)In(x)Sb on InAs may be better than that of the interface of InAs on Ga(1-x)In(x)Sb, but the abruptness of the interfaces would still be compatible. The RHEED intensity variations in the formation of the interfaces are discussed in terms of interface chemical reactions.

Fan, W. C.↗

NASA NTRS1991

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, thereby avoiding frictional effects. An F/M interface toughness test based on this configuration would provide data for K(sub I)/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, R. A.↗

NASA NTRS1991

Effect of thermal convection on the shape of a solid-liquid interface

The effect of thermal convection on the shape of solid-liquid interface was investigated in experiments conducted in a transparent Bridgman-type directional solidification furnace. The relationship was numerically modeled using a standard 2D finite-difference approach, with the solid-liquid deformable interface approximated by a blocking-off technique. The directional solidification furnace was used with pure succinonitrile (which is also transparent) contained in a long square ampoule made of borosilicate glass. With the furnace in the vertical configuration, a flat interface was observed, in agreement with the model. On the other hand, a highly distorted interface was obtained in the horizontal configuration; the numerical results showed a strong recirculating cell in front of the interface due to natural thermal convection. The results indicate that thermal convection is responsible for the interface distortion.

Mennetrier, C.↗

NASA NTRS1992

Fracture mechanics analysis for various fiber/matrix interface loadings

Fiber/matrix (F/M) cracking was analyzed to provide better understanding and guidance in developing F/M interface fracture toughness tests. Two configurations, corresponding to F/M cracking at a broken fiber and at the free edge, were investigated. The effects of mechanical loading, thermal cooldown, and friction were investigated. Each configuration was analyzed for two loadings: longitudinal and normal to the fiber. A nonlinear finite element analysis was performed to model friction and slip at the F/M interface. A new procedure for fitting a square-root singularity to calculated stresses was developed to determine stress intensity factors (K sub I and K sub II) for a bimaterial interface crack. For the case of F/M cracking at a broken fiber with longitudinal loading, crack tip conditions were strongly influenced by interface friction. As a result, an F/M interface toughness test based on this case was not recommended because nonlinear data analysis methods would be required. For the free edge crack configuration, both mechanical and thermal loading caused crack opening, theory avoiding fractional effects. A F/M interface toughness test based on this configuration would provide data for K(sub I/K(sub II) ratios of about 0.7 and 1.6 for fiber and radial normal loading, respectively. However, thermal effects must be accounted for in the data analysis.

Naik, Rajiv A.↗

NASA NTRS1989

User interface support

Space construction will require heavy investment in the development of a wide variety of user interfaces for the computer-based tools that will be involved at every stage of construction operations. Using today's technology, user interface development is very expensive for two reasons: (1) specialized and scarce programming skills are required to implement the necessary graphical representations and complex control regimes for high-quality interfaces; (2) iteration on prototypes is required to meet user and task requirements, since these are difficult to anticipate with current (and foreseeable) design knowledge. We are attacking this problem by building a user interface development tool based on extensions to the spreadsheet model of computation. The tool provides high-level support for graphical user interfaces and permits dynamic modification of interfaces, without requiring conventional programming concepts and skills.

Lewis, Clayton↗

NASA NTRS1990

Virtual workstations and telepresence interfaces: Design accommodations and prototypes for Space Station Freedom evolution

An advanced human-system interface is being developed for evolutionary Space Station Freedom as part of the NASA Office of Space Station (OSS) Advanced Development Program. The human-system interface is based on body-pointed display and control devices. The project will identify and document the design accommodations ('hooks and scars') required to support virtual workstations and telepresence interfaces, and prototype interface systems will be built, evaluated, and refined. The project is a joint enterprise of Marquette University, Astronautics Corporation of America (ACA), and NASA's ARC. The project team is working with NASA's JSC and McDonnell Douglas Astronautics Company (the Work Package contractor) to ensure that the project is consistent with space station user requirements and program constraints. Documentation describing design accommodations and tradeoffs will be provided to OSS, JSC, and McDonnell Douglas, and prototype interface devices will be delivered to ARC and JSC. ACA intends to commercialize derivatives of the interface for use with computer systems developed for scientific visualization and system simulation.

Mcgreevy, Michael W.↗

NASA NTRS1992

XPI: The Xanadu Parameter Interface

XPI is a table driven parameter interface which greatly simplifies both command driven programs such as BROWSE and XIMAGE as well as stand alone single-task programs. It moves all of the syntax and semantic parsing of commands and parameters out of the users code into common code and externally defined tables. This allows the programmer to concentrate on writing the code unique to the application rather than reinventing the user interface and for external graphical interfaces to interface with no changes to the command driven program. XPI also includes a compatibility library which allows programs written using the IRAF host interface (Mandel and Roll) to use XPI in place of the IRAF host interface.

White, N.↗

NASA NTRS1992

Integrating a local database into the StarView distributed user interface

A distributed user interface to the Space Telescope Data Archive and Distribution Service (DADS) known as StarView is being developed. The DADS architecture consists of the data archive as well as a relational database catalog describing the archive. StarView is a client/server system in which the user interface is the front-end client to the DADS catalog and archive servers. Users query the DADS catalog from the StarView interface. Query commands are transmitted via a network and evaluated by the database. The results are returned via the network and are displayed on StarView forms. Based on the results, users decide which data sets to retrieve from the DADS archive. Archive requests are packaged by StarView and sent to DADS, which returns the requested data sets to the users. The advantages of distributed client/server user interfaces over traditional one-machine systems are well known. Since users run software on machines separate from the database, the overall client response time is much faster. Also, since the server is free to process only database requests, the database response time is much faster. Disadvantages inherent in this architecture are slow overall database access time due to the network delays, lack of a 'get previous row' command, and that refinements of a previously issued query must be submitted to the database server, even though the domain of values have already been returned by the previous query. This architecture also does not allow users to cross correlate DADS catalog data with other catalogs. Clearly, a distributed user interface would be more powerful if it overcame these disadvantages. A local database is being integrated into StarView to overcome these disadvantages. When a query is made through a StarView form, which is often composed of fields from multiple tables, it is translated to an SQL query and issued to the DADS catalog. At the same time, a local database table is created to contain the resulting rows of the query. The returned rows are displayed on the form as well as inserted into the local database table. Identical results are produced by reissuing the query to either the DADS catalog or to the local table. Relational databases do not provide a 'get previous row' function because of the inherent complexity of retrieving previous rows of multiple-table joins. However, since this function is easily implemented on a single table, StarView uses the local table to retrieve the previous row. Also, StarView issues subsequent query refinements to the local table instead of the DADS catalog, eliminating the network transmission overhead. Finally, other catalogs can be imported into the local database for cross correlation with local tables. Overall, it is believe that this is a more powerful architecture for distributed, database user interfaces.

Silberberg, D. P.↗

NASA NTRS1993

Towards the formal specification of the requirements and design of a processor interface unit

Work to formally specify the requirements and design of a Processor Interface Unit (PIU), a single-chip subsystem providing memory interface, bus interface, and additional support services for a commercial microprocessor within a fault-tolerant computer system, is described. This system, the Fault-Tolerant Embedded Processor (FTEP), is targeted towards applications in avionics and space requiring extremely high levels of mission reliability, extended maintenance free operation, or both. The approaches that were developed for modeling the PIU requirements and for composition of the PIU subcomponents at high levels of abstraction are described. These approaches were used to specify and verify a nontrivial subset of the PIU behavior. The PIU specification in Higher Order Logic (HOL) is documented in a companion NASA contractor report entitled 'Towards the Formal Specification of the Requirements and Design of a Processor Interfacs Unit - HOL Listings.' The subsequent verification approach and HOL listings are documented in NASA contractor report entitled 'Towards the Formal Verification of the Requirements and Design of a Processor Interface Unit' and NASA contractor report entitled 'Towards the Formal Verification of the Requirements and Design of a Processor Interface Unit - HOL Listings.'

Fura, David A.↗

NASA NTRS1994

Hardware interface for isolation of vibrations in flexible manipulators: Development and applications

NASA's Langley Research Center (LaRC) is addressing the problem of isolating the vibrations of the Shuttle remote manipulator system (RMS) from its end-effector and/or payload by modeling an RMS flat-floor simulator with a dynamic payload. Analysis of the model can lead to control techniques that will improve the speed, accuracy, and safety of the RMS in capturing satellites and eventually facilitate berthing with the space station. Rockwell International Corporation, also involved in vibration isolation, has developed a hardware interface unit to isolate the end-effector from the vibrations of an arm on a Shuttle robotic tile processing system (RTPS). To apply the RTPS isolation techniques to long-reach arms like the RMS, engineers have modeled the dynamics of the hardware interface unit with simulation software. By integrating the Rockwell interface model with the NASA LaRC RMS simulator model, investigators can study the use of a hardware interface to isolate dynamic payloads from the RMS. The interface unit uses both active and passive compliance and damping for vibration isolation. Thus equipped, the RMS could be used as a telemanipulator with control characteristics for capture and berthing operations. The hardware interface also has applications in industry.

Manouchehri, Davoud↗

NASA NTRS1996

The Integrated Mode Management Interface

Mode management is the processes of understanding the character and consequences of autoflight modes, planning and selecting the engagement, disengagement and transitions between modes, and anticipating automatic mode transitions made by the autoflight system itself. The state of the art is represented by the latest designs produced by each of the major airframe manufacturers, the Boeing 747-400, the Boeing 777, the McDonnell Douglas MD-11, and the Airbus A320/A340 family of airplanes. In these airplanes autoflight modes are selected by manipulating switches on the control panel. The state of the autoflight system is displayed on the flight mode annunciators. The integrated mode management interface (IMMI) is a graphical interface to autoflight mode management systems for aircraft equipped with flight management computer systems (FMCS). The interface consists of a vertical mode manager and a lateral mode manager. Autoflight modes are depicted by icons on a graphical display. Mode selection is accomplished by touching (or mousing) the appropriate icon. The IMMI provides flight crews with an integrated interface to autoflight systems for aircraft equipped with flight management computer systems (FMCS). The current version is modeled on the Boeing glass-cockpit airplanes (747-400, 757/767). It runs on the SGI Indigo workstation. A working prototype of this graphics-based crew interface to the autoflight mode management tasks of glass cockpit airplanes has been installed in the Advanced Concepts Flight Simulator of the CSSRF of NASA Ames Research Center. This IMMI replaces the devices in FMCS equipped airplanes currently known as mode control panel (Boeing), flight guidance control panel (McDonnell Douglas), and flight control unit (Airbus). It also augments the functions of the flight mode annunciators. All glass cockpit airplanes are sufficiently similar that the IMMI could be tailored to the mode management system of any modern cockpit. The IMMI does not replace the functions of the FMCS control and display unit. The purpose of the INMI is to provide flight crews with a shared medium in which they can assess the state of the autoflight system, take control actions on it, reason about its behavior, and communicate with each other about its behavior. The design is intended to increase mode awareness and provide a better interface to autoflight mode management. This report describes the IMMI, the methods that were used in designing and developing it, and the theory underlying the design and development processes.

Hutchins, Edwin↗

NASA NTRS1995

AIAA spacecraft GN&C interface standards initiative: Overview

The American Institute of Aeronautics and Astronautics (AIAA) has undertaken an important standards initiative in the area of spacecraft guidance, navigation, and control (GN&C) subsystem interfaces. The objective of this effort is to establish standards that will promote interchangeability of major GN&C components, thus enabling substantially lower spacecraft development costs. Although initiated by developers of conventional spacecraft GN&C, it is anticipated that interface standards will also be of value in reducing the development costs of micro-engineered spacecraft. The standardization targets are specifically limited to interfaces only, including information (i.e. data and signal), power, mechanical, thermal, and environmental interfaces between various GN&C components and between GN&C subsystems and other subsystems. The current emphasis is on information interfaces between various hardware elements (e.g., between star trackers and flight computers). The poster presentation will briefly describe the program, including the mechanics and schedule, and will publicize the technical products as they exist at the time of the conference. In particular, the rationale for the adoption of the AS1773 fiber-optic serial data bus and the status of data interface standards at the application layer will be presented.

Challoner, A. Dorian↗

NASA NTRS1996

Solidification Interface Shape and Location During Processing in High Gradient Furnace with Quench

High Gradient Furnace with Quench (HGFQ) is being developed to facilitate metals processing experiments aboard the International Space Station. The sample is centered in an annular furnace and is held fixed during processing. The furnace itself is made to translate over the sample. Once in process, heat will flow through the sample from the Heater Zone to the Chill Zone. If operating conditions are correct, the solidification interface will stand in the gradient zone. Objectives of the HGFQ process are to provide a high gradient for the solidification with the solidification interface properly positioned in the gradient zone. At the recent RDR for HGFQ, one of the panelists raised the question about the suitability of HGFQ for potential future PIs. Specifically, it was stated by the design team at RDR that the present HGFQ design would provide a radius of curvature of the solidification interface of at least one sample diameter. The RDR panel argued that this was too small, and that most investigators would need a radius of curvature larger than this. The requirements established by the current PIs are shown. These requirements do not contain any specification about the interface shape. However, these requirements do define the envelope of operational parameters for HGFQ. The objectives of the present investigation are to 1) determine a suitable means of quantifying the interface shape, and 2) investigate the interface shape and how it is affected by processing parameters. The processing parameters to be considered are 1) sample material, 2) sample diameter, and 3) gradient zone length.

Woodbury, Keith A.↗

NASA NTRS1998

An Object-Oriented Interface to the CCSDS Ground Telecommand Services

The Telecommand Data Routing and Channel Services defined by the Consultative Committee for Space Data Systems (CCSDS) are flexible enough to support a myriad of commanding models. Because the standard is so broad, the traditional approach has been to implement only the portion of the standard needed by the particular spacecraft being tested/operated. Tasked with providing Telecommand Services for an entire class of spacecraft, where each spacecraft may choose any valid CCSDS commanding model, NASA Code 584 designed a common architecture capable of handling the full CCSDS protocol. The solution uses another CCSDS standard - the Standard Formatted Data Unit (SFDU) as the interface to the Telecommand Services. SFDUs provide a consistent way of labelling data objects, as well as allowing data objects to encapsulate other data objects. The resulting interface is: - Flexible: The full Data Routing and Channel Services are available via a single interface. The client (i.e. the command source) may enter commands at any layer within the protocol stack, specify any of the data aggregation or segmentation methods, and dynamically set any configuration parameter defined in the standard. - Object-oriented: Each object specifies both the data and the actions to be performed with the data. An object may contain other objects. - Expandable: New capabilities are added by defining new objects. Objects pass thru the protocol layers until they reach the applicable layer. The resulting design is: - Modular: The logic for each protocol layer is contained in a separate Application Program Interface (API). The objects used for the external interface are also used for communication between layers. - Distributable: The design can be split along any layer boundary for distribution across multiple machines. The objects ensure data consistency across platforms. This paper describes the SFDU-based interface and the resulting protocol implementation. The implementation is currently used by NASA (National Aeronautics and Space Administration) for integration & test of the microwave Anisotropy Probe (MAP) and Earth observer-I (EO-l) spacecraft. It will be used for post-launch operations of these spacecraft as well as the Imager for Magnetopause to Aurora Global Exploration (IMAGE) spacecraft.

Ray, Timothy Joseph↗

NASA NTRS1999

Determination of the Solid/Liquid Interface Shape and Resultant Radial Homogeneity in Directionally Solidified Hg(0.89)Mn(0.11)Te

Directional solidification and interrupted directional solidification experiments were used to determine tile shape of the solid/liquid interface and the resultant radial homogeneity in Hg(0.89)Mg(0.11)Te. For directionally solidified samples solidified at a rate of 0.09 microns/sec in a thermal gradient of 83 C/cm, a maximum of 0.006 molar percent MnTe radial variation across the Hg0.89)Mn(0.11)Te boules at specific locations was determined using an FTIR technique. This FTIR evaluation of the radial homogeneity also indicated an asymmetrical, convex interface shape during solidification. The asymmetrical, convex shape of the growth interface was confirmed by interrupted directional solidification experiments. These were performed under the same growth conditions as the normally completed directional solidification experiments except that the samples were quenched before the final growth transient was reached. In these experiments, etching and scanning X-ray fluorescence were used to reveal the shape of the solid/liquid interface. Microprobe analysis of composition gradients across the interface was used to confirm the authors' previous work in evaluating the segregation coefficient of Hg(0.89)Mn(0.11)Te alloy. Microprobe analysis of the interface region of the interrupted growth sample revealed a dendritic structure containing secondary and tertiary dendritic arms.

Price, M. W.↗

NASA NTRS2001

MPLM On-Orbit Interface Dynamic Flexibility Modal Test

Now that the International Space Station (ISS) is being constructed, payload developers have to not only verify the Shuttle-to-payload interface, but also the interfaces their payload will have with the ISS. The Multi Purpose Logistic Module (MPLM) being designed and built by Alenia Spazio in Torino, Italy is one such payload. The MPLM is the primary carrier for the ISS Payload Racks, Re-supply Stowage Racks, and the Resupply Stowage Platforms to re-supply the ISS with food, water, experiments, maintenance equipment and etc. During the development of the MPLM there was no requirement for verification of the on-orbit interfaces with the ISS. When this oversight was discovered, all the dynamic test stands had already been disassembled. A method was needed that would not require an extensive testing stand and could be completed in a short amount of time. The residual flexibility testing technique was chosen. The residual flexibility modal testing method consists of measuring the free-free natural frequencies and mode shapes along with the interface frequency response functions (FRF's). Analytically, the residual flexibility method has been investigated in detail by, MacNeal, Martinez, Carne, and Miller, and Rubin, but has not been implemented extensively for model correlation due to difficulties in data acquisition. In recent years improvement of data acquisition equipment has made possible the implementation of the residual flexibility method as in Admire, Tinker, and Ivey, and Klosterman and Lemon. The residual flexibility modal testing technique is applicable to a structure with distinct points (DOF) of contact with its environment, such as the MPLM-to-Station interface through the Common Berthing Mechanism (CBM). The CBM is bolted to a flange on the forward cone of the MPLM. During the fixed base test (to verify Shuttle interfaces) some data was gathered on the forward cone panels. Even though there was some data on the forward cones, an additional modal test was performed to better characterize its behavior. The CBM mounting flange is the only remaining structure of the MPLM that no test data was available. This paper discusses the implementation of the residual flexibility modal testing technique on the CBM flange and the modal test of the forward cone panels.

Bookout, Paul S.↗

NASA NTRS2001

Particle Engulfment and Pushing By Solidifying Interfaces

The phenomenon of interaction of particles with solid-liquid interfaces (SLI) has been studied since the mid 1960's. While the original interest stemmed from geology applications (frost heaving in soil), researchers soon realized that fundamental understanding of particles behavior at solidifying interfaces might yield practical benefits in other fields, including metallurgy. In materials engineering the main issue is the location of particles with respect to grain boundaries at the end of solidification. Considerable experimental and theoretical research was lately focused on applications to metal matrix composites produced by casting or spray forming techniques, and on inclusion management in steel. Another application of particle SLI interaction is in the growing of Y1Ba2Cu3O(7-delta) (123) superconductor crystals from an undercooled liquid. The oxide melt contains Y2Ba1Cu1O5 (211) precipitates, which act as flux pinning sites. The experimental evidence on transparent organic materials, as well as the recent in situ observations on steel demonstrates that there exist a critical velocity of the planar SLI below which particles are pushed ahead of the interface, and above which particles are engulfment. The engulfment of a SiC particle in succinonitrile is exemplified. However, in most commercial alloys dendritic interfaces must be considered. Indeed, most data available on metallic alloys are on dendritic structures. The term engulfment is used to describe incorporation of a particle by a planar or cellular interface as a result of local interface perturbation, as opposed to entrapment that implies particle incorporation at cells or dendrites boundaries. During entrapment the particles are pushed in the intercellular or interdendritic regions and then captured when local solidification occurs. The physics of these two phenomena is fundamentally different.

Stefanescu, Doru M.↗

NASA NTRS1997

Molecular Dynamics of Peptide Folding at Aqueous Interfaces

Even though most monomeric peptides are disordered in water they can adopt sequence-dependent, ordered structures, such as a-helices, at aqueous interfaces. This property is relevant to cellular signaling, membrane fusion, and the action of toxins and antibiotics. The mechanism of folding nonpolar peptides at the water-hexane interface was studied in the example of an 11-mer, of poly-L-leucine. Initially placed as a random coil on the water side of the interface, the peptide folded into an a-helix in 36 ns. Simultaneously, the peptide translocated into the hexane side of the interface. Folding was not sequential and involved a 3/10-helix as an intermediate. The folded peptide was either parallel to the interface or had its C-terminus exposed to water. An 11-mer, LQQLLQQLLQL, composed of leucine (L) and glutamine (G), was taken as a model amphiphilic peptide. It rapidly adopted an amphiphilic, disordered structure at the interface. Further folding proceeded through a series of amphiphilic intermediates.

Pohorille, Andrew↗