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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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NASA NTRS1989

From primal sketches to the recovery of intensity and reflectance representations

A local change in intensity (edge) is a characteristic that is preserved when an image is filtered through a bandpass filter. Primal sketch representations of images, using the bandpass-filtered data, have become a common process since Marr proposed his model for early human vision. Here, researchers move beyond the primal sketch extraction to the recovery of intensity and reflectance representations using only the bandpass-filtered data. Assessing the response of an ideal step edge to the Laplacian of Gaussian (NAb/A squared G) filter, they found that the resulting filtered data preserves the original change of intensity that created the edge in addition to the edge location. Using the filtered data, they can construct the primal sketches and recover the original (relative) intensity levels between the boundaries. It was found that the result of filtering an ideal step edge with the Intensity-Dependent Spatial Summation (IDS) filter preserves the actual intensity on both sides of the edge, in addition to the edge location. The IDS filter also preserves the reflectance ratio at the edge location. Therefore, one can recover the intensity levels between the edge boundaries as well as the (relative) reflectance representation. The recovery of the reflectance representation is of special interest as it erases shadowing degradations and other dependencies on temporal illumination. This method offers a new approach to low-level vision processing as well as to high data-compression coding. High compression can be gained by transmitting only the information associated with the edge location (edge primitives) that is necessary for the recovery

Alter-Gartenberg, Rachel↗
NASA NTRS1998

Deciphering the Long-Term Trend of Atlantic Basin Intense Hurricanes: More Active Versus Less Active During the Present Epoch

During the interval of 1944-1997, 120 intense hurricanes (i.e., those of category 3 or higher on the Saffir-Simpson hurricane damage potential scale) were observed in the Atlantic basin, having an annual frequency of 0-7 events per year, being more active prior to the mid 1960's than thereafter (hence a possible two-state division: more active versus less active), and being preferentially lower during El Nino years as compared to non-El Nino years. Because decadal averages of the frequency of intense hurricanes closely resemble those of average temperature anomalies for northern hemispheric and global standards and of the average temperature at the Armagh Observatory (Northern Ireland), a proxy for climatic change, it is inferred that the long-term trends of the annual frequency of intense hurricanes and temperature may be statistically related. Indeed, on the basis of 4- and 10-yr moving averages, one finds that there exists strong linear associations between the annual frequency of intense hurricanes in the Atlantic basin and temperature (specially, when temperature slightly leads). Because the long-term leading trends of temperature are now decidedly upward, beginning about the mid 1980's, it is inferred that the long-term consequential trends of the annual frequency of intense hurricanes should now also be upward, having begun near 1990, suggesting that a return to the more active state probably has already occurred. However, because of the anomalous El Nino activity of the early to mid 1990's, the switch from the less active to the more active state essentially went unnoticed (a marked increase in the number of intense hurricanes was not observed until the 1995 and 1996 hurricane seasons, following the end of the anomalous El Nino activity). Presuming that a return to the more active state has, indeed, occurred, one expects the number of seasonal intense hurricanes during the present epoch (continuing through about 2012) to usually be higher than average (i.e., greater than or equal to 2), except during El Nino-related seasons when the number usually will be less than average.

Wilson, Robert M.↗
NASA NTRS2000

Intensity Biased PSP Measurement

The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Volmer Equation) between intensity ratio (I(sub 0)/I) and pressure ratio (P/P(sub 0)) over a wide range of pressures (vacuum to ambient or higher). Although this may be valid for some PSPs, in most PSPs the relationship is nonlinear, particularly at low pressures (less than 0.2 psia when the oxygen level is low). This non-linearity can be attributed to variations in the oxygen quenching (de-activation) rates (which otherwise is assumed constant) at these pressures. Other studies suggest that some paints also have non-linear calibrations at high pressures; because of heterogeneous (non-uniform) oxygen diffusion and c quenching. Moreover, pressure sensitive paints require correction for the output intensity due to light intensity variation, paint coating variation, model dynamics, wind-off reference pressure variation, and temperature sensitivity. Therefore to minimize the measurement uncertainties due to these causes, an in- situ intensity correction method was developed. A non-oxygen quenched paint (which provides a constant intensity at all pressures, called non-pressure sensitive paint, NPSP) was used for the reference intensity (I(sub NPSP)) with respect to which all the PSP intensities (I) were measured. The results of this study show that in order to fully reap the benefits of this technique, a totally oxygen impermeable NPSP must be available.

Subramanian, Chelakara S.↗
NASA NTRS2000

Intensity Biased PSP Measurement

The current pressure sensitive paint (PSP) technique assumes a linear relationship (Stern-Volmer Equation) between intensity ratio (I(sub o)/I) and pressure ratio (P/P(sub o)) over a wide range of pressures (vacuum to ambient or higher). Although this may be valid for some PSPs, in most PSPs the relationship is nonlinear, particularly at low pressures (less than 0.2 psia when the oxygen level is low). This non-linearity can be attributed to variations in the oxygen quenching (de-activation) rates (which otherwise is assumed constant) at these pressures. Other studies suggest that some paints also have non-linear calibrations at high pressures; because of heterogeneous (non-uniform) oxygen diffusion and quenching. Moreover, pressure sensitive paints require correction for the output intensity due to light intensity variation, paint coating variation, model dynamics, wind-off reference pressure variation, and temperature sensitivity. Therefore to minimize the measurement uncertainties due to these causes, an insitu intensity correction method was developed. A non-oxygen quenched paint (which provides a constant intensity at all pressures, called non-pressure sensitive paint, NPSP) was used for the reference intensity (I(sub NPSP) with respect to which all the PSP intensities (I) were measured. The results of this study show that in order to fully reap the benefits of this technique, a totally oxygen impermeable NPSP must be available.

Subramanian, Chelakara S.↗
NASA NTRS2016

Human Influence on Tropical Cyclone Intensity

Recent assessments agree that tropical cyclone intensity should increase as the climate warms. Less agreement exists on the detection of recent historical trends in tropical cyclone intensity.We interpret future and recent historical trends by using the theory of potential intensity, which predicts the maximum intensity achievable by a tropical cyclone in a given local environment. Although greenhouse gas-driven warming increases potential intensity, climate model simulations suggest that aerosol cooling has largely canceled that effect over the historical record. Large natural variability complicates analysis of trends, as do poleward shifts in the latitude of maximum intensity. In the absence of strong reductions in greenhouse gas emissions, future greenhouse gas forcing of potential intensity will increasingly dominate over aerosol forcing, leading to substantially larger increases in tropical cyclone intensities.

Human influence on climate↗
NASA NTRS2011

Limits on Achievable Intensity Reduction with an Optical Occulter

Deep shadowing of a normally incident plane wave by an opaque circular disk is partially negated by the formation of a region of strong intensity surrounding the axis passing normally through the disk center. This local intensity enhancement, historically referred to as the Poisson Spot (also known as the Spot of Arago), has been the principal source of difficulties in applications where a significant reduction of the incident intensity is essential. In particular, the NASA Terrestrial Planet Finder's (TPF) mission requires suppression of direct starlight by at least 10 orders of magnitude over the entire visible spectral range. One technique that has been proposed for blocking the direct starlight is to use a rotationally symmetric disk with petallike segments along its boundary. We find that, even though such configurations could, indeed, theoretically provide the desired intensity reduction, they would require unreasonably small radii of curvature at the petals' tips (in the range of micrometers). When the radii of curvature are increased to 3 mm, the intensity reduction drops to a modest 5 to 6 orders of magnitude. Given that for the NASA's TPF mission the proposed occulter radius would be on the order of 25 m, even the 3 mm radius of curvature would be too small for any practical implementation. Further increases of the radius of curvature result in progressively poorer intensity suppression. As an alternative solution we propose an apodized circular disk. We show that with an optimized apodization function, intensity reductions of at least 10 orders of magnitude can be achieved over the entire visible spectral range. Numerical results are presented for parameters appropriate to the NASA TPF mission.

Wasylkiwskyj, Wasyl↗
NASA NTRS1971

Silicon solar cells as a high-solar-intensity radiometer

The characteristics of a conventional, 1- by 2-cm, N/P, gridded silicon solar cell when used as a radiometer have been determined for solar intensity levels to 2800 mW/sq cm (20 solar constants). The short-circuit current was proportional to the radiant intensity for levels only to 700 mW/sq cm (5 solar constants). For intensity levels greater than 700 mW/sq cm, it was necessary to operate the cell in a photoconductive mode in order to obtain a linear relation between the measured current and the radiant intensity. When the solar cell was biased with a reverse voltage of -1 V, the measured current and radiant intensity were linearly related over the complete intensity range from 100 to 2800 mW/sq cm.

Spisz, E. W.↗
NASA NTRS1971

Proposed characterization of tornadoes and hurricanes by area and intensity

Results of the 1968 through 1970 Tornado Watch Experiment conducted jointly by NASA and NOAA suggested the necessity of characterizing individual tornadoes in order to improve the identity of tornado-producing nephsystems. An attempt was made, therefore, to categorize each tornado by its intensity and area. Fujita-scale wind and corresponding damage categories were devised to classify tornadoes as Gale (F0), Weak (F1), Strong (F2), Severe (F3), Devastating (F4), and Incredible (F5). Additionally, individual tornado areas were also categorized as Trace (TR), Decimicro (DM), Micro (MI), Meso (ME), Marco (MA), Giant (GI), and Decagiant (DG), thus permitting characterizing of a tornado by a combination of intensity and area, such as weak decimicro tornado, severe meso tornado, or incredible giant tornado. A test characterization of 156 Japanese tornadoes in 1950-69 was accomplished for comparison with 893 U.S. tornadoes in 1965. Unexpectedly, the percentage distribution of intensity and individual area of U.S. and Japanese tornadoes is very similar except for large and/or intense ones. Intensity distribution within the Dallas and Fargo tornadoes of 1957 was also studied in detail. It was also found that the F-scale variation along the paths of family tornadoes shows an intensity oscillation with a 45-min interval.

Fujita, T. T.↗
NASA NTRS1975

Propagation of Sound at Moderate and High Intensities in Absorbent and Hard-Walled Cylindrical Ducts

The propagation of plane wave and higher order acoustic modes in both hard-walled and absorbent cylindrical ducts was studied at moderate sound intensities where the linear wave equation is valid, and at high intensities where nonlinear effects can be observed. The experiments were conducted with an anechoically terminated twelve-inch inside-diameter transite pipe. Various types of sound sources were mounted at one end of the duct to generate the desired acoustic fields within the duct. Arrays of conventional loudspeakers were used to generate plane waves and higher order acoustic modes at moderate intensities, and an array of four high intensity electro-pneumatic sound sources was used for the experiments in the nonlinear region. The attenuation of absorbent liners made of several different materials was obtained at moderate intensities for both plane waves and high order modes. It was found that the characteristics of the liners studied did not change appreciably at high intensities.

Mcdaniel, Oliver Herbert↗
NASA NTRS1976

Intensity measurements for the /2, O/ gamma-band of O2, b 1Sigma-g/+/ - X 3Sigma-g/-/

Line intensities for the P sub P and P sub Q branches of the (2-O) vibrational band of the magnetic dipole electronic transition for the oxygen red system at 6280 A were measured, and the sum of the R sub R and R sub Q branch intensities was taken. A large number of repetitive spectral scans were required for accuracy, because of low absorption values even at optical path lengths from 300 to 600 m. A total of 557 individual measurements of P-branch lines yielded an intensity value for the P-branches, and equivalent widths for 24 spectral scans yielded an intensity value for the R-branch. R-branch to P-branch intensity ratios were taken for the A-band, B-band, and gamma-band (respectively, O-O at 7620 A, 1-O at 6880 A, and 2-O at 6280 A). Intensities for some rotational lines are found, and effects of combined rotation-vibration interaction are probed.

Miller, J. H.↗
NASA NTRS1976

Low-energy electron intensities at large distances over the earth's polar cap

The eccentric-orbiting satellite Imp 5 penetrated the distant polar magnetosphere at positions corresponding to those for magnetic field lines which intersect the earth's northern polar cap. Measurements of electron intensities with E not less than 250 eV in these regions of extremely low plasma densities were gained with an electrostatic analyzer. The observational period was January-October 1970. Electron intensities within the energy range 250 eV-50 keV were less by orders of magnitude than those typically encountered within the plasma sheet and over the auroral oval. However, dramatic temporal variations of average electron intensities in the polar cap region were found for orbit-to-orbit comparisons. The observed intensity variations showed a remarkable correlation with the polarity of the magnetic sector structure in the interplanetary medium: high intensities for 'away from the sun' sectors and low intensities for 'toward' sectors.

Yeager, D. Y.↗
NASA NTRS1978

Intense magnetic fields at 1 AU: Solar cycle 20

Of the intense magnetic fields (greater than 13 gamma) observed at 1 AU during solar cycle 20 (1973-1975), 92% were associated with shocks, stream interfaces, or cold magnetic enhancements (CMEs). Most (52%) of the magnetic field intensity enhancements occurred at stream interfaces; 27% occurred behind shocks without interfaces; and 11% occurred in CMEs. The most intense fields (25 gamma to 37 gamma) followed shocks. Magnetic field intensities at interfaces did not exceed 25 gamma, suggesting a mechanism such as a magnetoacoustic wave limits the intensity ahead of streams. Intense magnetic fields persist longest behind shocks.

Burlaga, L. F.↗
NASA NTRS1982

A comparison of turbulence intensity measurements using a laser velocimeter and a hot wire in a low speed jet flow

The study involves a simultaneous measurement with both instruments along radial scans at two axial locations in the jet exiting from the turbulent pipe and an axial scan at the 75-percent radial location in the jet from the convergent nozzle. The results suggest that, within the limits of flow stationarity, both instruments yield measurements in good agreement, + or - 0.8-percent in turbulence intensity, below a turbulence intensity (the ensemble standard deviation divided by the local mean velocity) of 20 percent. From turbulence intensities of 20 percent to a maximum of 75 percent, the measurements exhibit the same trends; for reasons discussed here, however, the comparisons are not of the quality as those below 20 percent. It is found that correcting the turbulence intensity data for velocity bias errors increases the results by an average of 2 percent in turbulence intensity above the hot wire results and the uncorrected laser velocimeter data. The results are seen as calling into question the validity of using the velocity bias correction and time average techniques for turbulence intensity measurements.

Meyers, J. F.↗
NASA NTRS1989

Raman intensity as a probe of concentration near a crystal growing in solution

The feasibility of using Raman spectral scattering signals for measurements of concentration profiles near a crystal interface during growth or dissolution is discussed. With KH2PO4 (KDP) as a test material, optical multichannel analyzer (OMA) detection of a solute Raman vibrational band provided direct quantification of solute concentration with band intensity. The intersection of incident laser and Raman collection optics provided 3-D selective point measurements of the solution concentration field. Unlike many other techniques, the Raman band intensity is not sensitive to the typical temperature variations. Precision calibration of Raman intensity versus KDP concentration with less than 1 pct standard deviation error levels was demonstrated. A fiber optic, which sampled incident laser intensity and coupled it to the OMA, provided a fully synchronized monitor of fluctuations in laser power to correlate with observed Raman signals. With 1 W of laser power at the sample, good data statistics required eight repeated data collections at approximately 2.5 min collection. The accumulated time represents the concentration measurement time at one spatial location. Photomicroscopy documented a 30 micrometer diameter by 200 micrometer of laser Raman scattering region in the solution near the crystal surface. The laser beam was able to approach up to 25 micrometer from the crystal surface. However, a crystal surface reflected intensity contribution was weakly detectable. Nucleated microcrystals were seen in the crystal-growing solution. These microcrystals convect right up to the crystal surface and indicate no quiet diffusion region under normal gravity conditions. Translation of the solution cell with respect to the optics caused systematic intensity errors.

Wilkinson, R. Allen↗
NASA NTRS1992

Improvement in surface fatigue life of hardened gears by high-intensity shot peening

Two groups of carburized, hardened, and ground spur gears that were manufactured from the same heat vacuum induction melted vacuum arc melted (VIM VAR) AISI 9310 steel were endurance tested for surface fatigue. Both groups were manufactured with a standard ground 16 rms surface finish. One group was subjected to a shot peening (SP) intensity of 7 to 9A, and the second group was subjected to a SP intensity of 15 to 17A. All gears were honed after SP to a surface finish of 16 rms. The gear pitch diameter was 8.89 cm. Test conditions were a maximum Hertz stress of 1.71 GPa, a gear temperature of 350 K, and a speed of 10000 rpm. The lubricant used for the tests was a synthetic paraffinic oil with an additive package. The following results were obtained: The 10 pct. surface fatigue (pitting) life of the high intensity (15 to 17A) SPed gears was 2.15 times that of the medium intensity (7 to 9A) SPed gears, the same as that calculated from measured residual stress at a depth of 127 microns. The measured residual stress for the high intensity SPed gears was 57 pct. higher than that for the medium intensity SPed gears at a depth of 127 microns and 540 pct. higher at a depth of 51 microns.

Townsend, Dennis P.↗
NASA NTRS1995

Temporal variation of meandering intensity and domain-wide lateral oscillations of the Gulf Stream

The path of the Gulf Stream exhibits two modes of variability: wavelike spatial meanders associated with instability processes and large-sale lateral shifts of the path presumably due to atmospheric forcing. The objectives of this study are to examine the temporal variation of the intensity of spatial meandering in the stream, to characterize large-scale lateral oscillations in the stream's path, and to study the correlation betwen these two dynamically distinct modes of variability. The data used for this analysis are path displacemets ofthe Gulf Stream between 75 deg and 60 deg W obtained from AVHRR-derived (Advanced Very High Resolution Radiometer) infrared images for the period April 1982 through December 1989. Meandering intensity, measured by the spatial root-mean-sqaure displacement of the stream path, displays a 9-month dominant periodicity which is persistent through the study period. The 9-month fluctuation in meandering intensity may be related to the interaction of Rosseby waves with the stream. Interannual variation of meandering intensity is also found to be significant, with meandering being mich more intense during 1985 than it was in 1987. Annual variation, however,is weak and not well-defined.The spatially averaged position of the stream, which reflects nonmeandering large-scale lateral oscillations of the stream path, is dominated by an annual cycle. On average, the mean position is farthest north in November and farthest south in April. The first empirical orthogonal function mode of the space-time path displacements represents lateral oscillatins that are in-phase over the space-time domain. Interannual oscillations are also observed and are found to be weaker than the annual oscillation. The eigenvalue of the first mode indicates that about 21.5% of the total space-time variability of the stream path can be attibuted to domain-wide lateral oscillation. The correlation between meandering intensity and domain-wide lateral oscillations is very weak.

Lee, Tong↗
NASA NTRS1998

Statistical Aspects of ENSO Events (1950-1997) and the El Nino-Atlantic Intense Hurricane Activity Relationship

On the basis of Trenberth's quantitative definition for marking the occurrence of an El Nino (or La Nina), one can precisely identify by month and year the starts and ends of some 15 El Nino and 10 La Nina events during the interval of 1950-1997, an interval corresponding to the most reliable for cataloging intense hurricane activity in the Atlantic basin (i.e., those of category 3-5 on the Saffir-Simpson hurricane scale). The main purpose of this investigation is primarily two-fold: First, the statistical aspects of these identified extremes and the intervening periods between them (called "interludes") are examined and, second, the statistics of the seasonal frequency of intense hurricanes in comparison to the extremes and interludes are determined. This study clearly demonstrates that of the last 48 hurricane seasons, 20 (42 percent) can be described as being "El Nino-related" (i.e., an El Nino was in progress during all, or part, of the yearly hurricane season--June-November), 13 (27 percent) as "La Nina-related" (i.e., a La Nina was in progress during all, or part, of the yearly hurricane season), and 15 (31 percent) as "interlude-related" (i.e., neither an El Nino nor a La Nina was in progress during any portion of the yearly hurricane season). Combining the latter two subgroups into a single grouping called "non-El Nino-related" seasons, one finds that they have had a mean frequency of intense hurricanes measuring 2.8 events per season, while the El Nino-related seasons have had a mean frequency of intense hurricanes measuring 1.3 events per season, where the observed difference in the means is inferred to be statistically important at the 99.8-percent level of confidence. Therefore, as previously shown more than a decade ago using a different data set, there undeniably exists an El Nino-Atlantic hurricane activity relationship, one which also extends to the class of intense hurricanes. During the interval of 1950-1997, fewer intense hurricanes occurred during El Nino-related seasons (always less than or equal to 3 and usually less than or equal to 2, this latter value having been true for 18 of the 20 El Nino-related seasons), while more usually occurred during non-El Nino-related seasons (typically greater than or equal to 2, having been true for 22 of the 28 non-El Nino-related seasons). Implications for the 1998 and 1999 hurricane seasons are discussed.

Wilson, Robert M.↗
NASA NTRS1998

Trends in the Annual Frequency of Atlantic Basin Intense Hurricanes: Implications for the Near-Term

During the interval of 1944-1997, 120 intense hurricanes (category 3, 4, or 5 on the Saffir-Simpson hurricane scale) have been observed in the Atlantic basin. These intense hurricanes have had an observed annual frequency of 0-7 events per year (having a mean, mode, and median equal to about 2 events per year), being preferentially lower during El Ninio years and higher during non-El Ninio years. Also, it has recently been established that a long-term downward trend in the annual frequency of intense hurricanes, spanning about five decades, has taken place, although this trend can, alternatively, be explained as a shift from a more active state prior to the mid 1960's to a less active state thereafter (rather than as a simple linear decline). In this paper, on the basis of 10-yr moving averages, the long4erm trend of the frequency of intense hurricanes is compared against one for the annual mean temperature at Armagh Observatory, Northern Ireland (which serves as a proxy for climatic change). Interestingly, the two sets of 10-yr moving averages correlate extremely well, especially, when incorporating a slight 6-yr lag between them (with temperature leading; r = 0.90). This suggests that the current leading trend of temperature, which had been downward, but now is upward, may portend a return to the more active state for intense hurricanes. Thus, the 1998 season (presuming the abatement of El Ninio prior to the start of the hurricane season), and for several years thereafter (at least, into the early years of the next millennium), may have an annual frequency of intense hurricanes that is commensurate with the previously observed active state that was seen prior to the mid 1960's. If true, then, the shift to the more active state, probably, occurred in the mid-to-late 1980's, apparently, having gone undetected because of the masking, or modulating, effect of El Ninio, which has been rampant since the mid-to-late 1980's.

Wilson, Robert M.↗