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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Predicting the maximum amplitude for the sunspot cycle from the rate of rise in sunspot number

The paper examines the relationship between the maximum amplitude for the sunspot cycle and the rate of rise during the ascending phase. It is found that, prior to about 2 yr into the cycle, the rate of rise is not a reliable predictor for maximum amplitude. Only during the second half of the ascent do the fits display strong linearity, having a correlation coefficient of r = 0.9 and a standard error Syx less than about 20.

Wilson, Robert M.↗
NASA NTRS1989

Correlation studies between solar wind parameters and the decimetric radio emission from Jupiter

Results of a study comparing long-term time variations in Jupiter's synchrotron radio emission with a variety of solar wind parameters and the 10.7 cm solar flux are reported. Data from 1963 through 1985 were analyzed, and the results suggest that many solar wind parameters are correlated with the intensity of the synchrotron emission produced by the relativistic electrons in the Jovian Van Allen radiation belts. Significant nonzero correlation coefficients appear to be associated with solar wind ion density, ram pressure, thermal pressure, flow velocity, momentum, and ion temperature. The implication of these results is that the solar wind is influencing the supply and/or loss of electrons to Jupiter's inner magnetosphere.

Bolton, S. J.↗
NASA NTRS1989

Spectral characterization of igneous rocks in the 8- to 12-micron region

This paper investigates the crystal-chemistry basis for the variation in spectral behavior of ingneous rocks, with the purpose of developing relationships useful for applications in the lithologic characterization of terrestrial and extraterrestrial surfaces. A new parameter is proposed for characterizing general rock and mineral type. The parameter, SCFM, defined as the ratio SiO2/(SiO2 + CaO + FeO + MgO), reflects the degree of depolymerization of the silica tetrahedra in both fine-grained and coarse-grained igneous rocks, and is a good descriptor of the composition of these rocks. Using spectra obtained in the laboratory on coarse-particulate mineral and solid-rock samples, the SCFM parameter was used to assess the effects of variations in the rock composition on the location, number, and width of spectral bands. A regression analysis of bands varying in width from 0.2 micron to 1.4 microns versus the SCFM value resulted in correlation coefficients ranging from 0.88 to 0.97.

Walter, Louis S.↗
NASA NTRS1989

Experimental tests of methods for the measurement of rainfall rate using an airborne dual-wavelength radar

Several attenuation-based methods for estimating the rainfall rate were applied to measurements made by an airborne dual-wavelength radar operating at 0.87 cm, the K(a)-band, and at 3 cm, the X-band. These methods included the traditional Z-R methods, designated Z(X)-R and Z(K)-R for the X- and K(a) band wavelengths, respectively; single- and dual-wavelength surface reference techniques (SRT and DSRT, respectively); and standard dual-wavelength methods with and without range-averaging. As the primary sources of error for these methods are nearly independent, agreement among the rain rates obtained with these methods would lend confidence in the results. Correlation coefficients obtained between the rainfall rates with the Z(X)-R and DSRT methods were generally between 0.7 and 0.9. Good agreement among the methods occurred most often in stratiform rain for rain rates betwen a few mm/hr to about 15 mm/hr, i.e., where attenuation at the shorter wavelength is significant but not so severe as to result in a loss of signal.

Meneghini, R.↗
NASA NTRS1989

Rectangular subsonic jet flow field measurements

Flow field measurements are presented of 3 subsonic rectangular cold air jets. The 3 cases presented had aspect ratios of 1 x 2, 1 x 4 at a Mach number of 0.09 and an aspect ratio of 1 x 2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemoneter system. The presented data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data is presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made. All tabular data are available in ASCII format on MS-DOS compatible disks.

Morrison, Gerald L.↗
NASA NTRS1989

Methods for trend analysis: Examples with problem/failure data

Statistics are emphasized as an important role in quality control and reliability. Consequently, Trend Analysis Techniques recommended a variety of statistical methodologies that could be applied to time series data. The major goal of the working handbook, using data from the MSFC Problem Assessment System, is to illustrate some of the techniques in the NASA standard, some different techniques, and to notice patterns of data. Techniques for trend estimation used are: regression (exponential, power, reciprocal, straight line) and Kendall's rank correlation coefficient. The important details of a statistical strategy for estimating a trend component are covered in the examples. However, careful analysis and interpretation is necessary because of small samples and frequent zero problem reports in a given time period. Further investigations to deal with these issues are being conducted.

Church, Curtis K.↗
NASA NTRS1990

Review and statistical analysis of the ultrasonic velocity method for estimating the porosity fraction in polycrystalline materials

A review and statistical analysis of the ultrasonic velocity method for estimating the porosity fraction in polycrystalline materials is presented. Initially, a semi-empirical model is developed showing the origin of the linear relationship between ultrasonic velocity and porosity fraction. Then, from a compilation of data produced by many researchers, scatter plots of velocity versus percent porosity data are shown for Al2O3, MgO, porcelain-based ceramics, PZT, SiC, Si3N4, steel, tungsten, UO2,(U0.30Pu0.70)C, and YBa2Cu3O(7-x). Linear regression analysis produced predicted slope, intercept, correlation coefficient, level of significance, and confidence interval statistics for the data. Velocity values predicted from regression analysis for fully-dense materials are in good agreement with those calculated from elastic properties.

Roth, D. J.↗
NASA NTRS1990

Rectangular subsonic jet flow field measurements

Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made.

Morrison, Gerald L.↗
NASA NTRS1989

Predictability of process resource usage - A measurement-based study on UNIX

A probabilistic scheme is developed to predict process resource usage in UNIX. Given the identity of the program being run, the scheme predicts CPU time, file I/O, and memory requirements of a process at the beginning of its life. The scheme uses a state-transition model of the program's resource usage in its past executions for prediction. The states of the model are the resource regions obtained from an off-line cluster analysis of processes run on the system. The proposed method is shown to work on data collected from a VAX 11/780 running 4.3 BSD UNIX. The results show that the predicted values correlate well with the actual. The correlation coefficient betweeen the predicted and actual values of CPU time is 0.84. Errors in prediction are mostly small. Some 82 percent of errors in CPU time prediction are less than 0.5 standard deviations of process CPU time.

Devarakonda, Murthy V.↗
NASA NTRS1990

Interplanetary Alfven waves and auroral (substorm) activity - IMP 8

Almost 1 year of IMP 8 interplanetary magnetic field and plasma data (days 1-312, 1979) have been examined to determine the interplanetary causes of geomagnetic AE activity. The nature of the interplanetary medium (Alfvenic or non-Alfvenic) and the B(s) correlation with AE were examined over 12-hour increments throughout the study. It is found that Alfvenic wave intervals are present over 60 percent of the time, and the southward component of the Alfven waves is well correlated with AE (average peak correlation coefficient 0.62), with a median lag of 43 min. From this statistical study, no major differences in the magnetospheric response to Alfvenic and non-Alfvenic intervals were obvious. The high-intensity long-duration continuous AE activity (HILDCAA) events discussed previously by Tsurutani and Gonzales (1987) are demonstrated to be caused by the southward components of the Alfven waves, presumably through the process of magnetic reconnection.

Tsurutani, Bruce T.↗
NASA NTRS1990

Turbulence measurements and noise generation in a transonic cryogenic wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous measurements of unsteady total temperature and pressure were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients failed to show vorticity, entropy, or sound as the dominant mode of turbulence in the tunnel.

Ng, W. F.↗
NASA NTRS1990

Potential vorticity index

Using standard data analysis techniques, researchers explore the links between disturbance growth and quasi-geostrophic potential vorticity (PV) gradients; appearance and disappearance of cutoff lows and blocking highs and their relation to a zonal index (properly defined in terms of PV); and teleconnections between different flow patterns and their relation to the zonal index. It was found that the PV index and the eddy index correlate better than a zonal index (defined by zonal wind) and the eddy index. In the frequency domain there are three frequencies (.03, .07 and .17 cpd (cycle per day) corresponding to periods of 33, 14 and 6 days) at which PV index and the eddy index exhibit local maxima. The high correlation found at periods of 33 days is mainly due to eddy activity at high latitudes while the local correlation maxima found at the shorter periods are mainly due mid-latitude eddy activity. The correlation between the PV index and the geopotential height anomaly at 500 mb, at each grid point in the Northern Hemisphere, shows the existence of most of the teleconnection patterns summarized by Wallace and Gutzler (1981): the North Atlantic Oscillation, the North Pacific Oscillation, and the Pacific/North American patterns. Results show that the Isentropic Potential Vorticity (IPV) analysis can be a very useful and powerful tool when used to understand the dynamics of several large scale atmospheric systems. Although the data are limited to only one winter, and it is difficult to assess the statistical significance of the correlation coefficients presented here, the results are encouraging from physical viewpoint.

Barcilon, Albert↗
NASA NTRS1991

Biasing errors and corrections

The dependence of laser velocimeter measurement rate on flow velocity is discussed. Investigations outlining that any dependence is purely statistical, and is nonstationary both spatially and temporally, are described. Main conclusions drawn are that the times between successive particle arrivals should be routinely measured and the calculation of the velocity data rate correlation coefficient should be performed to determine if a dependency exists. If none is found, accept the data ensemble as an independent sample of the flow. If a dependency is found, the data should be modified to obtain an independent sample. Universal correcting procedures should never be applied because their underlying assumptions are not valid.

Meyers, James F.↗
NASA NTRS1989

Remote sensing of the thermal forcing on the tropical Pacific

Monthly fields of shortwave radiation (SR) and latent heat flux (LE) over the central and eastern tropical Pacific between 1980 and 1983 have been computed using satellite data. They are the dominant variable components of surface thermal forcing on the ocean in this time scale. During the 1982-1983 ENSO episode, surface-wind convergence and cloudiness associated with the displacement of equatorial organized convection caused a reduction in both the SR into the ocean and the LE out of the ocean. The lag-correlation coefficients between the forcing (SR-LE) and the sea surface temperature are found to be significantly high outside the equatorial region, showing that surface thermal forcing is the dominant factor in sea surface temperature change. In the narrow equatorial wave guide, ocean dynamics play a more important role, and surface heat flux is a consequence rather than the cause of sea surface temperature change.

Liu, W. Timothy↗
NASA NTRS1991

The structure of a passive scalar field with a uniform mean gradient in rapidly sheared homogeneous turbulent flow

The effect of an arbitrarily oriented mean passive scalar gradient on one-point passive scalar statistics is studied in homogeneous turbulent shear flow in the limit of rapid shearing. By neglecting the nonlinear inertial transfer to small scales an analytical solution for individual Fourier modes is obtained for the case of unity Prandtl number. This solution is used to compute the development of one-point statistics for the velocity and scalar fields in the inviscid limit. Comparisons to direct numerical simulations of the full nonlinear equations for the same flow show that, in addition to describing the early time response to the imposed shear, the linear solution gives reasonable estimates of several correlation coefficients for the developed shear flow.

Rogers, Michael M.↗
NASA NTRS1991

A study of the relationship between micropulsations and solar wind properties

A year-long comparison between daily averages of solar wind parameters obtained from the MIT experiment on IMP-8 and micropulsation measurements made by the Universita dell'Aquila has shown a correlation between solar wind speed and micropulsation power with peaks of the correlation coefficient greater than 0.8 in the period range from 20 to 40 s. Different behavior observed for different period bands suggests that the shorter period activity tends to precede the highest values of the solar wind speed while the longer period activity tends to persist for longer intervals within high velocity solar wind streams. A comparison with simultaneous interplanetary magnetic field measurements supports the upstream origin of the observed ground pulsations.

Yedidia, B. A.↗
NASA NTRS1991

Unsteady convection in tin in a Bridgman configuration

When a quiescent fluid is heated sufficiently from below, steady convection will begin. Further heating will cause oscillatory and then turbulent flow. Theoretical results predict that the frequency of oscillation will depend on the square root of the Rayleigh number in the fluid. In the current work, liquid tin was heated from below for three aspect ratios, h/R = 3.4, 5.3, and 7.0. The experimental results are curve-fit for the square-root relation and also for a linear relation. The fit of the expression is evaluated using a correlation coefficient. An estimate for the first critical Rayleigh number (onset of steady convection) is obtained for both expressions. These values are compared to previous experimental results.

Knuteson, David J.↗
NASA NTRS1991

Analysis of polarimetric SAR signatures of vegetated areas

Several techniques to quantitatively analyze the information in the polarimetric signature are discussed, including: (1) a shape (texture) parameter; (2) fractional polarization; (3) the phase difference signature; and (4) the correlation coefficient. These techniques are applied to airborne synthetic aperture radar imagery collected over several different vegetation communities, including a mangrove swamp, a mixed-age loblolly pine forest, and a flooded bald cypress forest.

French, Nancy H. F.↗