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At least 415 records · Page 23

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NASA NTRS1990

The application of CFD to rotary wing flow problems

Rotorcraft aerodynamics is especially rich in unsolved problems, and for this reason the need for independent computational and experimental studies is great. Three-dimensional unsteady, nonlinear potential methods are becoming fast enough to enable their use in parametric design studies. At present, combined CAMRAD/FPR analyses for a complete trimmed rotor soltution can be performed in about an hour on a CRAY Y-MP (or ten minutes, with multiple processors). These computational speeds indicate that in the near future many of the large CFD problems will no longer require a supercomputer. The ability to convect circulation is routine for integral methods, but only recently was it discovered how to do the same with differential methods. It is clear that the differential CFD rotor analyses are poised to enter the engineering workplace. Integral methods already constitute a mainstay. Ultimately, it is the users who will integrate CFD into the entire engineering process and provide a new measure of confidence in design and analysis. It should be recognized that the above classes of analyses do not include several major limiting phenomena which will continue to require empirical treatment because of computational time constraints and limited physical understanding. Such empirical treatment should be included, however, into the developing CFD, engineering level analyses. It is likely that properly constructed flow models containing corrections from physical testing will be able to fill in unavoidable gaps in the experimental data base, both for basic studies and for specific configuration testing. For these kinds of applications, computational cost is not an issue. Finally, it should be recognized that although rotorcraft are probably the most complex of aircraft, the rotorcraft engineering community is very small compared to the fixed-wing community. Likewise, rotorcraft CFD resources can never achieve fixed-wing proportions and must be used wisely. Therefore the fixed-wing work must be gleaned for many of the basic methods.

Caradonna, F. X.↗

NASA NTRS1990

Contour-map encoding of shape for early vision

Contour maps provide a general method for recognizing 2-D shapes. All but blank images give rise to such maps, and people are good at recognizing objects and shapes from them. The maps are encoded easily in long feature vectors that are suitable for recognition by an associative memory. These properties of contour maps suggest a role for them in early visual perception. The prevalence of direction sensitive neurons in the visual cortex of mammals supports this view.

Kanerva, Pentti↗

NASA NTRS1990

Establishing a center for advanced space propulsion

The goals and the concept of NASA-sponsored Centers for the Commercial Development of Space (CCDSs) are presented. The Center for Advanced Space Propulsion (CASP), its research projects, and the prognosis for their success are discussed. The establishment of CCDSs is recognized as an experiment to bring together university and industry researchers to maintain and improve the internationally competitive position of the United States in space. Increasing private investment in space-related technology and developing new commercial products are the basic requirements for success. CASP is the only CCDS that focuses on propulsion technology, which is critical to ensuring continued U.S. leadership in space. CASP is expected to become a recognized center for propulsion research and commercialization within the next five years.

Garrison, George W.↗

NASA NTRS1992

Modified Synthetic-Discriminant-Function Optical Filter

Experiments demonstrated feasibility of synthetic-discriminant-function filter encoded in binary spatial light modulator. Filter is part of optoelectronic apparatus indicating degree of correlation between input image and any number of training images of same object at various positions and orientations. Used in optical correlator to recognize rotated images, or in tracking system to recognize moving vehicle or other substantially rigid object from any direction.

Reid, Max B.↗

NASA NTRS1991

Asteroid flux and impact cratering rate on Venus

By the end of 1990, 65 Venus-crossing asteroids were recognized; these represent 59 percent of the known Earth-crossing asteroids. Further studies, chiefly numerical integrations of orbit evolution, may reveal one or two more Venus crossers among the set of discovered asteroids. A Venus crosser was defined as an asteroid whose orbit can intersect the orbit of Venus as a result of secular (long range) perturbations. Venus crossers revolving on orbits that currently overlap the orbit of Venus are called Venapol asteroids, and those on orbit that don't overlap are called Venamor asteroids; 42 Venapols and 23 Venamors were recognized. Collision probabilities with Venus for 60 of the known Venus crossers were determined.

Shoemaker, E. M.↗

NASA NTRS1991

Concepts, requirements, and design approaches for building successful planning and scheduling systems

Traditional practice of systems engineering management assumes requirements can be precisely determined and unambiguously defined prior to system design and implementation; practice further assumes requirements are held static during implementation. Human-computer decision support systems for service planning and scheduling applications do not conform well to these assumptions. Adaptation to the traditional practice of systems engineering management are required. Basic technology exists to support these adaptations. Additional innovations must be encouraged and nutured. Continued partnership between the programmatic and technical perspective assures proper balance of the impossible with the possible. Past problems have the following origins: not recognizing the unusual and perverse nature of the requirements for planning and scheduling; not recognizing the best starting point assumptions for the design; not understanding the type of system that being built; and not understanding the design consequences of the operations concept selected.

Hornstein, Rhoda Shaller↗

NASA NTRS1992

Real-time demonstration hardware for enhanced DPCM video compression algorithm

The lack of available wideband digital links as well as the complexity of implementation of bandwidth efficient digital video CODECs (encoder/decoder) has worked to keep the cost of digital television transmission too high to compete with analog methods. Terrestrial and satellite video service providers, however, are now recognizing the potential gains that digital video compression offers and are proposing to incorporate compression systems to increase the number of available program channels. NASA is similarly recognizing the benefits of and trend toward digital video compression techniques for transmission of high quality video from space and therefore, has developed a digital television bandwidth compression algorithm to process standard National Television Systems Committee (NTSC) composite color television signals. The algorithm is based on differential pulse code modulation (DPCM), but additionally utilizes a non-adaptive predictor, non-uniform quantizer and multilevel Huffman coder to reduce the data rate substantially below that achievable with straight DPCM. The non-adaptive predictor and multilevel Huffman coder combine to set this technique apart from other DPCM encoding algorithms. All processing is done on a intra-field basis to prevent motion degradation and minimize hardware complexity. Computer simulations have shown the algorithm will produce broadcast quality reconstructed video at an average transmission rate of 1.8 bits/pixel. Hardware implementation of the DPCM circuit, non-adaptive predictor and non-uniform quantizer has been completed, providing realtime demonstration of the image quality at full video rates. Video sampling/reconstruction circuits have also been constructed to accomplish the analog video processing necessary for the real-time demonstration. Performance results for the completed hardware compare favorably with simulation results. Hardware implementation of the multilevel Huffman encoder/decoder is currently under development along with implementation of a buffer control algorithm to accommodate the variable data rate output of the multilevel Huffman encoder. A video CODEC of this type could be used to compress NTSC color television signals where high quality reconstruction is desirable (e.g., Space Station video transmission, transmission direct-to-the-home via direct broadcast satellite systems or cable television distribution to system headends and direct-to-the-home).

Bizon, Thomas P.↗

NASA NTRS1990

An upward compatible spectrum sharing architecture for existing, actively planned and emerging mobile satellite systems

Existing and actively planned mobile satellite systems are competing for a viable share of the spectrum allocated by the International Telecommunications Union (ITU) to the satellite based mobile services in the 1.5/1.6 GHz range. The limited amount of spectrum available worldwide and the sheer number of existing and planned mobile satellite systems dictate the adoption of an architecture which will maximize sharing possibilities. A viable sharing architecture must recognize the operational needs and limitations of the existing systems. Furthermore, recognizing the right of access of the future systems as they will emerge in time, the adopted architecture must allow for additional growth and be amenable to orderly introduction of future systems. An attempt to devise such a sharing architecture is described. A specific example of the application of the basic concept to the existing and planned mobile satellite systems is also discussed.

Azarbar, Bahman↗

NASA NTRS1992

Artificial neural network implementation of a near-ideal error prediction controller

A theory has been developed at the University of Virginia which explains the effects of including an ideal predictor in the forward loop of a linear error-sampled system. It has been shown that the presence of this ideal predictor tends to stabilize the class of systems considered. A prediction controller is merely a system which anticipates a signal or part of a signal before it actually occurs. It is understood that an exact prediction controller is physically unrealizable. However, in systems where the input tends to be repetitive or limited, (i.e., not random) near ideal prediction is possible. In order for the controller to act as a stability compensator, the predictor must be designed in a way that allows it to learn the expected error response of the system. In this way, an unstable system will become stable by including the predicted error in the system transfer function. Previous and current prediction controller include pattern recognition developments and fast-time simulation which are applicable to the analysis of linear sampled data type systems. The use of pattern recognition techniques, along with a template matching scheme, has been proposed as one realizable type of near-ideal prediction. Since many, if not most, systems are repeatedly subjected to similar inputs, it was proposed that an adaptive mechanism be used to 'learn' the correct predicted error response. Once the system has learned the response of all the expected inputs, it is necessary only to recognize the type of input with a template matching mechanism and then to use the correct predicted error to drive the system. Suggested here is an alternate approach to the realization of a near-ideal error prediction controller, one designed using Neural Networks. Neural Networks are good at recognizing patterns such as system responses, and the back-propagation architecture makes use of a template matching scheme. In using this type of error prediction, it is assumed that the system error responses be known for a particular input and modeled plant. These responses are used in the error prediction controller. An analysis was done on the general dynamic behavior that results from including a digital error predictor in a control loop and these were compared to those including the near-ideal Neural Network error predictor. This analysis was done for a second and third order system.

Mcvey, Eugene S.↗

NASA NTRS1992

Geochemistry of lunar crustal rocks from breccia 67016 and the composition of the moon

The geochemistry of anorthositic clasts from an Apollo 16 breccia 67016 is studied in order to investigate the role of these rock types in lunar crustal evolution. The samples have aluminous, alkali-poor compositions and varied FeO and MgO contents. Three compositional groups are recognized. One group is poor in mafic constituents with low abundances of lithophile trace elements typical of lunar anorthosites, while the other two groups are more mafic and are distinguished from each other by FeO/MgO ratios greater than one in the case of ferroan noritic and less than one in the case of magnesian troctolitic. These mafic-enriched varieties have considerably higher lithophile element concentrations, at levels similar to that of the bulk lunar crust. The ferroan noritic clasts may represent a fundamental type of igneous rock in the lunar crust which has not been widely recognized.

Norman, Marc D.↗

NASA NTRS1992

Floor-fractured crater models of the Sudbury structure, Canada

The Sudbury structure in Ontario, Canada, is one of the oldest and largest impact structures recognized in the geological record. It is also one of the most extensively deformed and volcanically modified impact structures on Earth. Although few other terrestrial craters are recognized as volcanically modified, numerous impact craters on the Moon have been volcanically and tectonically modified and provide possible analogs for the observed pattern of modification at Sudbury. We correlate the pattern of early deformation at Sudbury to fracture patterns in two alternative lunar analogs and then use these analogs both to estimate the initial size of the Sudbury structure and to model the nature of early crater modification at Sudbury.

Wichman, R. W.↗

NASA NTRS1992

Gross-fragmentation of meteoroids and bulk density of Geminids from photographic fireball records

The explicit solution of the drag and ablation equations of a single nonfragmenting meteoroid moving in any actual atmosphere was published several years ago. The solution yields the theoretical relation of l, the distance flown by the meteoroid in its trajectory, as a function of time, t, assuming that the height, h, is a known function of l. The photographic records of meteors and fireballs are coded by time marks, using a rotating shutter or a similar device to break the moving image. Time is, thus, the independent variable and for each time mark on a meteoroid trajector, the observed distance along the trajectory, l sub obs, as well as the double- or multiple- station photographs of the same meteoroid. Applying this solution to all available Prairie Network (PN) fireball-records, we recognized that the majority of them gave good solutions with standard deviations somewhat bigger than the intrinsic geometrical precision of the data. We also noticed that, on an average, previous methods of evaluation of the meteoroid velocities (interpolation polynomials, numerical differenciation of the observed l sub obs) used up to only several tens of percent of the intrinsic precision of the PN observational data. When residuals of these solutions, i.e. l sub obs - l sub com, were represented as a function of time for about 75 percent of solutions. The remaining 25 percent of residuals showed systematic changes with time exceeding one standard deviation. We tried to explain these systematic time course of residuals by using different meteoroids first computed theoretically and then analyzed by the same model as the natural PN fireballs were. The conclusion of these model computations is that systematic time changes of residuals in the nonfragmenting model exceeding one standard of deviation are caused by sudden gross fragmentation at one or more trajectory points. Thus, we generalized the explicit solution of the drag and ablation equations of a single nonfragmenting meteoroid by allowing for one or more points, where sudden gross fragmentation can occur. Using this generalized solution, the distances along the meteoroid trajectory can be computed for any choice of input parameters and compared with the observed distances flown by the meteoroid. For the most precise and long fireball trajectories, the least-squares solution can, thus, yield the initial velocities, the ablation coefficients, the dynamical masses, the positions of gross-fragmentation points, and the terminal mass. At a gross-fragmentation point, the ratio of the main mass to all the remaining fragments can be compared with the dynamic mass determined from our gross-fragmentation model and, thus, the meteoroid bulk density can be evaluated. We applied the gross-fragmentation model to sever PN fireballs showing time changes of residuals, and we recognized that, in all these cases, the new computed bulk densities of meteoroids resulted higher in comparison with the meteoroid densities determined with the non-gross-fragmentation model. Other aspects of the study are discussed.

Ceplecha, Zdenek↗

NASA NTRS1992

Canadian Space Agency Space Station Freedom utilization plans

Under the terms of the NASA/CSA Memorandum of Understanding, Canada will contribute the Mobile Servicing System and be entitled to use 3 percent of all Space Station utilization resources and user accommodations over the 30 year life of the Station. Equally importantly Canada, like NASA, can begin to exploit these benefits as soon as the Man-Tended Capability (MTC) phase begins, in early 1997. Canada has been preparing its scientific community to fully utilize the Space Station for the past five years; most specifically by encouraging, and providing funding, in the area of Materials Science and Applications, and in the area of Space Life Sciences. The goal has been to develop potential applications and an experienced and proficient Canadian community able to effectively utilize microgravity environment facilities such as Space Station Freedom. In addition, CSA is currently supporting four facilities; a Laser Test System, a Large Motion Isolation Mount, a Canadian Float Zone Furnace, and a Canadian Protein Crystallization Apparatus. In late April of this year CSA sent out a Solicitation of Interest (SOI) to potential Canadian user from universities, industry, and government. The intent of the SOI was to determine who was interested, and the type of payloads which the community at large intended to propose. The SOI will be followed by the release of an Announcement of Opportunity (AO) following governmental approval of the Long Term Space plan later this year, or early next year. Responses to the AO will be evaluated and prioritized in a fair and impartial payload selection process, within the guidelines set by our international partners and the Canadian Government. Payload selection is relatively simple compared to the development and qualification process. An end-to-end user support program is therefore also being defined. Much of this support will be provided at the new headquarters currently being built in St. Hubert, Quebec. It is recognized that utilizing the Space Station could be expensive for users; costing in many cases millions of dollars to get a payload from conception to retrieval. It is also recognized that some of the potential users cannot or will not invest a lot of money or effort into Space Station utilization, unless there is a perceived significant commercial potential. How best to fund Space Station payloads is under study. Space Station Freedom will provide the first opportunity for Canada to conduct experiments in a long-duration microgravity environment. CSA have been developing and funding potential users for some time, and considerable interest has been shown by the response to our SOI earlier this year. Canada can be one of the two earliest users for the Space Station, along with NASA. We hope to take full advantage of this opportunity.

Faulkner, James↗

NASA NTRS1993

Optical media standards for industry

Optical storage is a new and growing area of technology that can serve to meet some of the mass storage needs of the computer industry. Optical storage is characterized by information being stored and retrieved by means of diode lasers. When most people refer to optical storage, they mean rotating disk media, but there are 1 or 2 products that use lasers to read and write to tape. Optical media also usually means removable media. Because of its removability, there is a recognized need for standardization, both of the media and of the recording method. Industry standards can come about in one or more different ways. An industry supported body can sanction and publish a formal standard. A company may ship enough of a product that it so dominates an application or industry that it acquires 'standard' status without an official sanction. Such de facto standards are almost always copied by other companies with varying degrees of success. A governmental body can issue a rule or law that requires conformance to a standard. The standard may have been created by the government, or adopted from among many proposed by industry. These are often known as de jure standards. Standards are either open or proprietary. If approved by a government or sanctioning body, the standard is open. A de facto standard may be either open or proprietary. Optical media is too new to have de facto standards accepted by the marketplace yet. The proliferation of non-compatible media types in the last 5 years of optical market development have convinced many of the need for recognized media standards.

Hallam, Kenneth J.↗

NASA NTRS1993

Bifurcating optical pattern recognition in photorefractive crystals

A new concept and experimental demonstration of a bifurcating optical pattern recognizer that uses a nonlinear gain saturation memory medium such as a high-gain photorefractive crystal are presented. A barium titanate crystal is used as a typical example of the nonlinear medium for the demonstration of the bifurcating optical pattern recognizer.

Liu, Hua-Kuang↗

NASA NTRS1992

Structure of a human monoclonal antibody Fab fragment against gp41 of human immunodeficiency virus type

The three-dimensional structure of a human monoclonal antibody (Fab), which binds specifically to a major epitope of the transmembrane protein gp41 of the human immunodeficiency virus type 1, has been determined by crystallographic methods to a resolution of 2.7 A. It has been previously determined that this antibody recognizes the epitope SGKLICTTAVPWNAS, belongs to the subclass IgG1 (kappa), and exhibits antibody-dependent cellular cytotoxicity. The quaternary structure of the Fab is in an extended conformation with an elbow bend angle between the constant and variable domains of 175 degrees. Structurally, four of the hypervariable loops can be classified according to previously recognized canonical structures. The third hypervariable loops of the heavy (H3) and light chain (L3) are structurally distinct. Hypervariable loop H3, residues 102H-109H, is unusually extended from the surface. The complementarity-determining region forms a hydrophobic binding pocket that is created primarily from hypervariable loops L3, H3, and H2.

He, X. M.↗

NASA NTRS1992

Structure of a human monoclonal antibody Fab fragment against gp41 of human immunodeficiency virus type 1

The three-dimensional structure of a human monoclonal antibody (Fab), which binds specifically to a major epitope of the transmembrane protein gp41 of the human immunodeficiency virus type 1, has been determined by crystallographic methods to a resolution of 2.7 A. It has been previously determined that this antibody recognizes the epitope SGKLICTTAVPWNAS, belongs to the subclass IgG1 (kappa), and exhibits antibody-dependent cellular cytotoxicity. The quaternary structure of the Fab is in an extended conformation with an elbow bend angle between the constant and variable domains of 175 deg. Structurally, four of the hypervariable loops can be classified according to previously recognized canonical structures. The third hypervariable loops of the heavy (H3) and light chain (L3) are structurally distinct. Hypervariable loop H3, residues 102H-109H, is unusually extended from the surface. The complementarity-determining region forms a hydrophobic binding pocket that is created primarily from hypervariable loops L3, H3, and H2.

He, Xiao M.↗

NASA NTRS1993

Feature extraction and classification algorithms for high dimensional data

Feature extraction and classification algorithms for high dimensional data are investigated. Developments with regard to sensors for Earth observation are moving in the direction of providing much higher dimensional multispectral imagery than is now possible. In analyzing such high dimensional data, processing time becomes an important factor. With large increases in dimensionality and the number of classes, processing time will increase significantly. To address this problem, a multistage classification scheme is proposed which reduces the processing time substantially by eliminating unlikely classes from further consideration at each stage. Several truncation criteria are developed and the relationship between thresholds and the error caused by the truncation is investigated. Next an approach to feature extraction for classification is proposed based directly on the decision boundaries. It is shown that all the features needed for classification can be extracted from decision boundaries. A characteristic of the proposed method arises by noting that only a portion of the decision boundary is effective in discriminating between classes, and the concept of the effective decision boundary is introduced. The proposed feature extraction algorithm has several desirable properties: it predicts the minimum number of features necessary to achieve the same classification accuracy as in the original space for a given pattern recognition problem; and it finds the necessary feature vectors. The proposed algorithm does not deteriorate under the circumstances of equal means or equal covariances as some previous algorithms do. In addition, the decision boundary feature extraction algorithm can be used both for parametric and non-parametric classifiers. Finally, some problems encountered in analyzing high dimensional data are studied and possible solutions are proposed. First, the increased importance of the second order statistics in analyzing high dimensional data is recognized. By investigating the characteristics of high dimensional data, the reason why the second order statistics must be taken into account in high dimensional data is suggested. Recognizing the importance of the second order statistics, there is a need to represent the second order statistics. A method to visualize statistics using a color code is proposed. By representing statistics using color coding, one can easily extract and compare the first and the second statistics.

Lee, Chulhee↗