Diminishing Returns: How Many GNSS-RO Observations are Enough?
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Lunar reflectivity at 0.86-centimeter wavelength.
Measurement of backscattering of 0.86-cm circularly polarized radiation by 29 regions on the moon. Both circular polarizations were received. At a given angle of incidence, power received in the 'expected' polarization was greater for the highland regions than for the seas by roughly 1 dB. For moderately large angles of incidence phi, this return diminishes more rapidly than cosine phi, although perhaps not as rapidly as it does at longer wavelengths. The cross section of the whole moon is 5 plus or minus 2% of the geometric cross section; about 80% of the cross section is ascribable to diffuse scattering. The polarization ratio for the echoes varies smoothly with the angle of incidence, from 0.7 at the subradar point to 0.4 at 70 deg. The depolarization is the same for marial and highland regions, and at large angles of incidence it is the same as has been found at 23 and 68 cm by other workers.
Mccue, J. J. G.↗
Study of unconventional propulsion system concepts for use in a long range transport
The noise level of an uncoventional propulsion system for the next generation of subsonic, long-range transport aircraft is discussed. The desired noise level may be achieved by: (1) a fixed geometry, high bypass ratio turbofan with a geared two-stage fan and advanced acoustic treatment or (2) a moderate bypass ratio turbofan with a variable pitch two-stage fan, variable primary and duct nozzles, and advanced acoustic treatment. The geared fan system meets the noise goal with minimum economic penalty. Comparison of the noise levels at takeoff and landing in combination with the economic penalties required to achieve the lower noise levels at specific noise measuring stations, indicate that both area reduction and current certification prodedures should be used to ascertain the point of diminishing returns in establishing future noise goals.
Champagne, G. A.↗
An overview of artificial gravity
The unique characteristics of artificial gravity that affect human performance and physiology in an artificial gravity environment are reviewed. The rate at which these unique characteristics change decreases very rapidly with increasing radius of a rotating vehicle used to produce artificial gravity. Reducing their influence on human performance or physiology by increasing radius becomes a situation of very rapidly diminishing returns. A review of several elements of human performance has developed criteria relative to the sundry characteristics of artificial gravity. A compilation of these criteria indicates that the maximum acceptable rate of rotation, leg heaviness while walking, and material handling are the factors that define the minimum acceptable radius. The ratio of Coriolis force to artificial weight may also be significant. Based on current knowledge and assumptions for the various criteria, a minimum radius between 15.2 and 16.8 m seems desirable.
Ralph W. Stone Jr.↗
Display requirements for the final approach and landing phase of an RPV mission
A two part investigation was conducted to determine the display requirements for the final approach and landing phase of a remotely piloted vehicle (RPV) mission, and to assess the relative merits of several possible display configurations. The objective of the first part of the investigation was to obtain subjective assessments of several display configurations, and to select the most promising display concepts for subsequent evaluation in terms of performance measures. A basic display consisting of a perspective image of terrain and runway, a horizon bar and an aircraft symbol was used, and guidance symbology was added to the basic displaying selected state variables. Initial results suggested that as guidance symbology is added to the basic display, pilot acceptance tends to increase. A point of diminishing returns is eventually reached, however, when additional information produces too much clutter, and makes it difficult for the pilot to process the displayed information.
Howard, J. C.↗
Feasibility study of a step scanned omnidirectional communications antenna for an international magnetospheric explorer spacecraft
The results of this study has indicated that omnidirectional antennas requiring directive gains steered off broadside are limited by the feed system efficiencies. The directive gain can be increased to offset the feed losses, but this approach leads quickly to diminishing returns. While gains of 4.8 db appear feasible, a system gain of 3.0 db is considered practical. These results apply to antenna configurations limited in packaging volume to 10 cm diameter by 61 cm length.
Herskind, R. E.↗
Hydrogen production from coal using a nuclear heat source
A strong candidate for hydrogen production in the intermediate time frame of 1985 to 1995 is a coal-based process using a high-temperature gas-cooled reactor (HTGR) as a heat source. Expected process efficiencies in the range of 60 to 70% are considerably higher than all other hydrogen production processes except steam reforming of a natural gas. The process involves the preparation of a coal liquid, hydrogasification of that liquid, and steam reforming of the resulting gaseous or light liquid product. A study showing process efficiency and cost of hydrogen vs nuclear reactor core outlet temperature has been completed, and shows diminishing returns at process temperatures above about 1500 F. A possible scenario combining the relatively abundant and low-cost Western coal deposits with the Gulf Coast hydrogen users is presented which provides high-energy density transportation utilizing coal liquids and uranium.
Quade, R. N.↗
Landsat-D thematic mapper simulation using aircraft multispectral scanner data
A simulation of imagery from the upcoming Landsat-D Thematic Mapper was accomplished by using selected channels of aircraft 24-channel multispectral scanner data. The purpose was to simulate Thematic Mapper 30-meter resolution imagery, to compare its spectral quality with the original aircraft MSS data, and to determine changes in thematic classification accuracy for the simulated imagery. The original resolution of approximately 7.5 meters IFOV and simulated resolution of 15, 30, and 60 meters were used to indicate the trend of spectral quality and classification accuracy. The study was based in a 6.5 square kilometer area of urban Los Angeles having a diversity of land use. The original imagery was reduced in resolution by two related methods: pixel matrix averaging, and matrix smoothing with a unity box filter, followed by matrix averaging. Thematic land use classification using training sites and a Bayesian maximum-likelihood algorithm was performed at three levels of standard deviation - 1.0, 2.0, and 3.0 sigma. Plots of relative standard deviation showed that for larger training sites with a normal distribution of data, as the resolution decreased, the distribution range of density values decreased. Also, the classification accuracies for three levels of standard deviation increased as resolution decreased. However, the indication is that a point of diminishing returns had been reached, and 30 meters IFOV should be the best for multispectral classification of urban scenes.
Clark, J.↗
Landsat-D thematic mapper simulation in an urban area using aircraft multispectral scanner data
A simulation of imagery from the Landsat-D thematic mapper was conducted in order to determine its usefulness for urban land-use classification. Aircraft 24-channel multispectral scanner imagery of the Los Angeles area at 7.5-m resolution was processed digitally by means of matrix averaging and image smoothing techniques to simulate the 30-m resolution of the thematic mapper. Mean and standard deviation statistics of training sites for resolutions of 7.5, 15, 30 and 60 m were used to generate final classification maps. Plots of relative standard deviation showed that for larger training sites, as the resolution decreased, the distribution range of density values also decreased, while plots of relative classification accuracies showed that as resolution decreased, classification accuracies for three levels of standard deviation increased. A point of diminishing returns was indicated, however, confirming the utility of the resolution intended for Landsat-D.
Clark, J.↗
Model for determining vapor equilibrium rates in the hanging drop method for protein crystal growth
An engineering analysis of the rate of evaporation of solvent in the hanging drop method of protein crystal growth is presented. Results are applied to 18 drop and well arrangements commonly encountered in the laboratory. The chemical nature of the salt, drop size and shape, drop concentration, well size, well concentration, and temperature are taken into account. The rate of evaporation increases with temperature, drop size, and the salt concentration difference between the drop and the well. The evaporation in this model possesses no unique half-life. Once the salt in the drop achieves 80 percent of its final concentration, further evaporation suffers from the law of diminishing returns.
Baird, James K.↗
Evaporation kinetics in the hanging drop method of protein crystal growth
An engineering analysis of the rate of evaporation of solvent in the hanging drop method of protein crystal growth is presented; these results are applied to 18 different drop and well arrangements commonly encountered in the laboratory, taking into account the chemical nature of the salt, the drop size and shape, the drop concentration, the well size, the well concentration, and the temperature. It is found that the rate of evaporation increases with temperature, drop size, and with the salt concentration difference between the drop and the well. The evaporation possesses no unique half-life. Once the salt in the drop achieves about 80 percent of its final concentration, further evaporation suffers from the law of diminishing returns.
Baird, James K.↗
On testing of functionally equivalent components of fault-tolerant software
Six functionally equivalent programs were tested with specification based random and extremal/special value (ESV) test cases. Statement and branch coverage were used to measure and compare the attained testing effectiveness. It was observed that both measures reached a nearly steady state value after 25 to 75 random test cases. Coverage saturation curves appear to follow an exponential growth model. However, the steady state values for branch coverage of different components, but the same input cases, differed by as much as 22 percent. The effect is the result of the differences in the detailed structure of the components. Improvement in coverage provided by the random test data, after the ESV cases were executed, was only about 1 percent. Results indicate that extensive random testing can be a process of diminishing returns, and that in the FTS context functional ('black box') testing can provide a very uneven execution coverage of the functionally equivalent software, and therefore should be supplemented by structure based testing.
Vouk, Mladen A.↗
Problems and solutions for transition detection in cryogenic wind tunnels by infrared imaging
The authors analyzed the problems associated with the detection of boundary-layer transition to turbulence by using the IR imaging techique in cryogenic wind-tunnel testing. It is shown that testing at low temperatures forces this implementation to run against the physical laws of diminishing returns. The most difficult obstacle resulted from the considerable decrease in the overall level of IR radiation and the parallel shift of the bulk of the radiated energy to longer wavelengths, beyond 30 microns at 100 K. Some measures to alleviate the problem are described. The thermal signature of transition can be enhanced by allowing the flow in the wind tunnel to heat incrementally, thus inducing a transient heat transfer to the model. As a result, the model area under the turbulent regime is revealed by its higher heating rate compared to the laminar regime.
Gartenberg, Ehud↗
Thermal Fatigue Limitations of Continuous Fiber Metal Matrix Composites
The potential structural benefits of unidirectional, continuous-fiber, metal matrix composites (MMC's) are legendary. When compared to their monolithic matrices, MMC's possess superior properties such as higher stiffness and tensile strength, and lower coefficient of thermal expansion in the direction of the reinforcing fibers. As an added bonus, the MMC density will be lower if the fibers are less dense than the matrix matErial they replace. The potential has been demonstrated unequivocally both analytically and experimentally, especially at ambient temperatures. Successes prompted heavily-funded National efforts within the United States (USAF and NASA) and elsewhere to extend the promise of MMC's into the temperature regime wherein creep, stress relaxation, oxidation, and thermal fatigue damage mechanisms lurk. This is the very regime for which alternative high-temperature materials are becoming mandatory, since further enhancement of state- of-the-art monolithic alloys is rapidly approaching a point of diminishing returns.
Halford, Gary R.↗
International Ultraviolet Explorer Final Archive
CSC processed IUE images through the Final Archive Data Processing System. Raw images were obtained from both NDADS and the IUEGTC optical disk platters for processing on the Alpha cluster, and from the IUEGTC optical disk platters for DECstation processing. Input parameters were obtained from the IUE database. Backup tapes of data to send to VILSPA were routinely made on the Alpha cluster. IPC handled more than 263 requests for priority NEWSIPS processing during the contract. Staff members also answered various questions and requests for information and sent copies of IUE documents to requesters. CSC implemented new processing capabilities into the NEWSIPS processing systems as they became available. In addition, steps were taken to improve efficiency and throughput whenever possible. The node TORTE was reconfigured as the I/O server for Alpha processing in May. The number of Alpha nodes used for the NEWSIPS processing queue was increased to a maximum of six in measured fashion in order to understand the dependence of throughput on the number of nodes and to be able to recognize when a point of diminishing returns was reached. With Project approval, generation of the VD FITS files was dropped in July. This action not only saved processing time but, even more significantly, also reduced the archive storage media requirements, and the time required to perform the archiving, drastically. The throughput of images verified through CDIVS and processed through NEWSIPS for the contract period is summarized below. The number of images of a given dispersion type and camera that were processed in any given month reflects several factors, including the availability of the required NEWSIPS software system, the availability of the corresponding required calibrations (e.g., the LWR high-dispersion ripple correction and absolute calibration), and the occurrence of reprocessing efforts such as that conducted to incorporate the updated SWP sensitivity-degradation correction in May.
Source record↗
Accelerated Test Methods
Neural network systems were evaluated for use in predicting wear of mechanical systems. Three different neural network software simulation packages were utilized in order to create models of tribological wear tests. Representative simple, medium, and high complexity simulation packages were selected. Pin-on-disk, rub shoe, and four-ball tribological test data was used for training, testing, and verification of the neural network models. Results showed mixed success. The neural networks were able to predict results with some accuracy if the number of input variables was low or the amount of training data was high. Increased neural network complexity resulted in more accurate results, however there was a point of diminishing return. Medium complexity models were the best trade off between accuracy and computing time requirements. A NASA Technical Memorandum and a Society of Tribologists and Lubrication Engineers paper are being published which detail the work.
Jansen, Ralph↗
The Efficiency of Various Computers and Optimizations in Performing Finite Element Computations
With the advent of computers with many processors, it becomes unclear how to best exploit this advantage. For example, matrices can be inverted by applying several processors to each vector operation, or one processor can be applied to each matrix. The former approach has diminishing returns beyond a handful of processors, but how many processors depends on the computer architecture. Applying one processor to each matrix is feasible with enough ram memory and scratch disk space, but the speed at which this is done is found to vary by a factor of three depending on how it is done. The cost of the computer must also be taken into account. A computer with many processors and fast interprocessor communication is much more expensive than the same computer and processors with slow interprocessor communication. Consequently, for problems that require several matrices to be inverted, the best speed per dollar for computers is found to be several small workstations that are networked together, such as in a Beowulf cluster. Since these machines typically have two processors per node, each matrix is most efficiently inverted with no more than two processors assigned to it.
Marcus, Martin H.↗
Strain-Gage Loads Calibration Parametric Study
This paper documents a parametric study of various aircraft wing-load test features that affect the quality of the resultant derived shear, bending-moment, and torque strain-gage load equations. The effect of the following on derived strain-gage equation accuracy are compared: single-point loading compared with distributed loading, variation in applied test load magnitude, number of applied load cases, and wing-box-only compared with control-surface loading. The subject of this study is an extensive wing-load calibration test of the Active Aeroelastic Wing F/A-18 airplane. Selected subsets of the available test data were used to derive load equations using the linear regression method. Results show the benefit of distributed loading and the diminishing-return benefits of test load magnitudes and number of load cases. The use of independent check cases as a quality metric for the derived load equations is shown to overcome blind extrapolating beyond the load data used to derive the load equations.
Lokos, William A.↗