SEARCH · Engineering Papers

Results for “Correlation coefficient”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57

All sources NASA NTRS DOE OSTI

NASA NTRS1974

Active microwave measurement of soil water content

Measurements of radar backscatter from bare soil at 4.7, 5.9, and 7.1 GHz for incident angles of 0-70 deg have been analyzed to determine sensitivity to soil moisture. Because the effective depth of penetration of the radar signal is only about one skin depth, the observed signals were correlated with the moisture in a skin depth as characterized by the attenuation coefficient (reciprocal of skin depth). Since the attenuation coefficient is a monotonically increasing function of moisture density, it may also be used as a measure of moisture content over the distance involved, which varies with frequency and moisture content. The measurements show an approximately linear increase in scattering with attenuation coefficient of the soil at angles within 10 deg of vertical and all frequencies. At 4.7 GHz this increase continues relatively large out to 70 deg incidence, but by 7.1 GHz the sensitivity is much less even at 20 deg and practically gone at 50 deg.

Ulaby, F. T.↗

NASA NTRS1982

Sorption of noble gases by solids, with reference to meteorites. II - Chromite and carbon. III - Sulfides, spinels, and other substances; on the origin of planetary gases

The trapping of noble gases by chromite and carbon, two putative carriers of primordial noble gases in meteorites, was studied by synthesizing 19 samples in a Ne-Ar-Kr-Xe atmosphere at 440-720 K. Noble gas contents are found to approximately obey Henry's Law, but only slight correlations are found with composition, surface area, or adsorption temperature. Geometric mean distribution coefficients for bulk samples and HCl residues in 10 cu cm STP/g atm are: Xe 100, Kr 15, Ar 3.5, and Ne 0.62. Elemental fractionation data support the suggestion of Lewis et al. (1977) that chromite and carbon in C2 and C3 chondrites were formed by the reaction: Fe, Cr + 4CO yields (Fe, Cr)3O4 + 4C + carbides. In contrast to meteoritic minerals, the synthetic specimens show no isotopic fractionation of noble gases. In a subsequent study, attention is given to the cases of sulfides and spinels, on the way to consideration of the origin of planetary gases. Sulfides showed three distinctive trends relative to chromite or magnetite. The elemental fractionation pattern of Ar, Kr and Xe in meteorites, terrestrial rocks and planets resembles the adsorption patterns on the carbons, spinels, sulfides, and other solids studied. The high release temperature of meteoritic noble gases may be explained by transformation of the physisorbed or chemisorbed gas. The ready loss of meteoritic heavy gases on surficial oxidation is consistent with adsorption, as is the high abundance.

Yang, J.↗

NASA NTRS1990

Experimental determination of convective heat transfer coefficients in the separated flow region of the Space Shuttle Solid Rocket Motor

A series of cold flow heat transfer tests was conducted with a 7.5-percent scale model of the Space Shuttle Rocket Motor (SRM) to measure the heat transfer coefficients in the separated flow region around the nose of the submerged nozzle. Modifications were made to an existing 7.5 percent scale model of the internal geometry of the aft end of the SRM, including the gimballed nozzle in order to accomplish the measurements. The model nozzle nose was fitted with a stainless steel shell with numerous thermocouples welded to the backside of the thin wall. A transient 'thin skin' experimental technique was used to measure the local heat transfer coefficients. The effects of Reynolds number, nozzle gimbal angle, and model location were correlated with a Stanton number versus Reynolds number correlation which may be used to determine the convective heating rates for the full scale Space Shuttle Solid Rocket Motor nozzle.

Whitesides, R. Harold↗

NASA NTRS1992

Origin of the moon and lunar core formation

In a recent version of the giant impact hypothesis by O'Neill, the initial abundances of the siderophile elements in the lunar mantle were established not only by combining impactor material and proto-Earth material, but also by adding a late reduced veneer. O'Neal also appealed to the possible volatilities of some elements (Mo and W) under conditions of lunar accretion, and required the segregation of a small Ni-rich metallic core. An attempt to more rigorously model lunar core formation in the O'Neill scenario is made by correlating degree of partial melting to temperature and extrapolating the 1260 C partition coefficients to the appropriate temperatures along a constant redox buffer.

Hillgren, Valerie J.↗

NASA NTRS1968

A Subsonic Wind-Tunnel Study to Determine the Buffet and Static Aerodynamic Characteristics of a Systematic Series of Wings

A wind-tunnel investigation has been conducted in the Langley High-Speed 7- by 10-Foot Tunnel to determine the buffet and static aerodynamic characteristics of a systematic wing series at Mach numbers ranging from 0.23 to 0.94. The results have indicated that for a given Mach number, the wings which display superior aerodynamic efficiency characteristics generally display the highest buffet free lift coefficient. The characteristics exhibited by the wings which were considered have indicated that correlations can be made between the onset of buffet and selected divergences in the static aerodynamic characteristics. Axial force has been found to be the most sensitive static component to the onset of buffeting.

Ray, Edward J.↗

NASA NTRS2006

On the Stratospheric Chemistry of Hydrogen Cyanide

HCN profiles measured by solar occultation spectrometry during 10 balloon flights of the JPL MkIV instrument are presented. The HCN profiles reveal a compact correlation with stratospheric tracers. Calculations with a 2D-model using established rate coefficients for the reactions of HCN with OH and O(1D) severely underestimate the measured HCN in the middle and upper stratosphere. The use of newly available rate coefficients for these reactions gives reasonable agreement of measured and modeled HCN. An HCN yield of approx.30% from the reaction of CH3CN with OH is consistent with the measurements.

photochemical properties↗

NASA NTRS2014

Use of an OSSE to Evaluate Background Error Covariances Estimated by the 'NMC Method'

The NMC method has proven utility for prescribing approximate background-error covariances required by variational data assimilation systems. Here, untunedNMCmethod estimates are compared with explicitly determined error covariances produced within an OSSE context by exploiting availability of the true simulated states. Such a comparison provides insights into what kind of rescaling is required to render the NMC method estimates usable. It is shown that rescaling of variances and directional correlation lengths depends greatly on both pressure and latitude. In particular, some scaling coefficients appropriate in the Tropics are the reciprocal of those in the Extratropics. Also, the degree of dynamic balance is grossly overestimated by the NMC method. These results agree with previous examinations of the NMC method which used ensembles as an alternative for estimating background-error statistics.

Data Assimilation↗

NASA NTRS2023

Quantification of Global Cloud Properties with Use of Spherical Harmonic Functions

Spherical harmonic (SH) expansion is a useful tool to study any variable that has valid values at all latitudes and longitudes. The variable can be quantified as a sum of different spherical harmonic components, which are the spherical harmonic functions multiplied by their expansion coefficients. We find that the SH components of cloud radiative effect (CRE) have correlations with El Niño-Southern Oscillation (ENSO) and the Hadley Circulation (HC). In particular, the expansion degree 2 (l = 2) SH power spectrum component anomaly of CRE is strongly correlated with ENSO. The two dipole patterns appearing in the l = 2 SH component anomaly map can be reasonably explained by a known mechanism of ENSO’s impact on cloud properties. The l = 3 and l = 5 SH power spectrum components are correlated with HC intensity, whereas the l = 6 and l = 8 components are correlated with HC latitudinal widths. In ENSO warm and cold phases, the HC-correlated SH components have opposite anomalies, which suggests the impact of ENSO on HC. This study illustrates that the SH expansion technique provides a different perspective to study the impacts of large-scale atmospheric circulation on global cloud properties and radiative effects.

clouds↗

NASA NTRS2023

Cryogenic Flow Boiling in Microgravity: Effects of Reduced Gravity on Two-Phase Fluid Physics and Heat Transfer

With the growing interest in space exploration, cryogenic technologies involving two-phase flow and heat transfer are in high demand to successfully procure advanced space applications such as fuel depots and nuclear thermal propulsion (NTP) systems for deep space missions. However, the unique and extreme thermal properties of cryogenic fluids introduce distinct flow boiling fluid physics and energy transport phenomena, which differ significantly from those observed with conventional fluids. Understanding the unique two-phase physics in cryogenic flow boiling remains an ongoing challenge. Furthermore, the lack of readily available microgravity cryogenic steady-state heat transfer data hinders the assessment of gravitational effects on cryogenic flow boiling. This study aims to elucidate the gravitational effects on two-phase fluid physics and heat transfer by conducting the first-ever experimental measurement of cryogenic flow boiling performance using a steady-state heated method in a reduced gravity environment. Parabolic flight experiments were performed to acquire both heat transfer measurements and high-speed video of interfacial behaviors, under varying gravity levels (microgravity, hypergravity, Lunar gravity, and Martian gravity). The experiments involved flow boiling of liquid nitrogen (LN 2 ) with a near-saturated inlet along a circular heated tube of dimensions 8.5-mm inner diameter and 680-mm heated length. The operating parameters varied are mass velocity of 398.3 - 1342.8 kg/m2s, inlet quality of -0.08 to -0.01, and inlet pressure of 413.68 - 689.48 kPa. Captured microgravity flow patterns range from bubbly to annular, all having vapor structures that are larger than those under higher gravity levels. Under microgravity, absence of buoyancy yields symmetrical vapor structures without flow stratification, laying a physical foundation for the distinct two-phase heat transfer trends during LN 2 flow boiling in microgravity. Transient data collected during the flight parabolas exhibited decreasing heated wall temperature as the aircraft transitioned from hypergravity to microgravity phases. The temperature variation indicated an enhancement in flow boiling heat transfer with decreasing gravity levels and a reduction with increasing gravity levels. The effect of reduced gravity on cryogenic flow boiling heat transfer coefficient (HTC) is discussed based on steady state heat transfer analysis. Seminal HTC correlations are evaluated against the measured microgravity HTC data, of which one is identified for superior accuracy in predicting microgravity data. Finally, a new HTC correlation is proposed to improve accuracy of microgravity predictions, yet there still exists room for further improvement with future terrestrial flow boiling experiments at different flow orientations relative to Earth gravity.

Microgravity↗

NASA NTRS1987

High frequency ultrasonic characterization of sintered SiC

High frequency (60 to 160 MHz) ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90 to 98 percent of theoretical, average grain sizes ranging from 3.0 to 12.0 microns, and average pore sizes ranging from 1.5 to 4.0 microns. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. Attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size.

Baaklini, George Y.↗

NASA NTRS1981

The role of magnetic helicity in cosmic ray transport theory

The pitch angle scattering of cosmic ray is modified greatly if the medium through which they propagate contains significant amounts of magnetic helicity. When helicity is present in the medium, the often used expression for the pitch angle diffusion coefficient derived from quasilinear theory must be modified. These modifications are illustrated for slab and isotropic symmetries. Using measurements of helicity in the solar wind determined from single point measurements of the correlation tensor of magnetic fluctuations obtained from Voyager 2, the effects of the observed helicity on both the pitch angle and spatial diffusion coefficients are estimated.

Goldstein, M. L.↗

NASA NTRS1969

Heat-Transfer Measurements Obtained on the X-15 Airplane Including Correlations With Wind-Tunnel Results

Heat-transfer measurements were obtained on the X-15 airplane from two flights under quasi-steady conditions at a free-stream Mach number of 5.1 and an angle of attack of 2.0° and a free-stream Mach number of 4.98 and an angle of attack of 16.3°. These measurements were made at corresponding free-stream Reynolds numbers of 2.45 × 10 6 and 1.31 × 10 6 per foot (8.04 × 10 6 and 4.30 × 10 6 per meter). Experimental heat-transfer coefficients derived from temperatures obtained from 200 recording thermocouples on the skin of the airplane are tabulated. Correlations with wind-tunnel results show that the wind-tunnel data are in fair-to-good agreement with the flight data obtained on the wing, ventral tail, and vertical tail at low angles of attack but are generally in poor agreement with the high-angle-of-attack data and the low-angle-of-attack fuselage data.

Robert D Quinn↗

NASA NTRS2001

The A6Sigma+ - X6Sigma+ Transition of CrH, Einstein Coefficients and an Improved Description of the A State

The spectrum of CrH has been reinvestigated in the 9000-15000/cm region using the Fourier transform spectrometer of the National Solar Observatory. The 1-0 and 1-1 bands of the A6Sigma+ - X6Sigma+ transition have been measured and improved spectroscopic constants have been determined. A value for the 2-0 band origin has been obtained from the band head using estimated spectroscopic constants. These data provide a set of much improved equilibrium vibrational and rotational constants for the A6Sigma+ state. An accurate description of the A-X transition has been obtained using a multi-reference configuration interaction approach. The inclusion of both scalar relativity and Cr 3s3p correlation are required to obtain a good description of both states. The ab initio computed Einstein coefficients and radiative lifetimes are reported.

Bauschlicher, Charles W., Jr.↗

NASA NTRS2017

Simulating PACE Global Ocean Radiances

The NASA PACE mission is a hyper-spectral radiometer planned for launch in the next decade. It is intended to provide new information on ocean biogeochemical constituents by parsing the details of high resolution spectral absorption and scattering. It is the first of its kind for global applications and as such, poses challenges for design and operation. To support pre-launch mission development and assess on-orbit capabilities, the NASA Global Modeling and Assimilation Office has developed a dynamic simulation of global water-leaving radiances, using an ocean model containing multiple ocean phytoplankton groups, particulate detritus, particulate inorganic carbon (PIC), and chromophoric dissolved organic carbon (CDOC) along with optical absorption and scattering processes at 1 nm spectral resolution. The purpose here is to assess the skill of the dynamic model and derived global radiances. Global bias, uncertainty, and correlation are derived using available modern satellite radiances at moderate spectral resolution. Total chlorophyll, PIC, and the absorption coefficient of CDOC (aCDOC), are simultaneously assimilated to improve the fidelity of the optical constituent fields. A 5-year simulation showed statistically significant (P < 0.05) comparisons of chlorophyll (r = 0.869), PIC (r = 0.868), and a CDOC (r =0.890) with satellite data. Additionally, diatoms (r = 0.890), cyanobacteria (r = 0.732), and coccolithophores (r = 0.716) were significantly correlated with in situ data. Global assimilated distributions of optical constituents were coupled with a radiative transfer model (Ocean-Atmosphere Spectral Irradiance Model, OASIM) to estimate normalized water-leaving radiances at 1 nm for the spectral range 250-800 nm. These unassimilated radiances were within 0.074 mW/sq cm/micron/sr of MODIS-Aqua radiances at 412, 443, 488, 531, 547, and 667 nm. This difference represented a bias of 10.4% (model low). A mean correlation of 0.706 (P < 0.05) was found with global distributions of MODIS radiances. These results suggest skill in the global assimilated model and resulting radiances. The reported error characterization suggests that the global dynamical simulation can support some aspects of mission design and analysis. For example, the high spectral resolution of the simulation supports investigations of band selection. The global nature of the radiance representations supports investigations of satellite observing scenarios. Global radiances at bands not available in current and past missions support investigations of mission capability. PACE, ocean color, water-leaving radiances, biogeochemical model, radiative transfer model

PIC↗

NASA NTRS1989

High-frequency ultrasonic characterization of sintered silicon carbide

High-frequency 60- to 160-MHz ultrasonic nondestructive evaluation was used to characterize variations in density and microstructural constituents of sintered SiC bars. Ultrasonic characterization methods included longitudinal velocity, reflection coefficient, and precise attenuation measurements. The SiC bars were tailored to provide bulk densities ranging from 90 to 98 percent of theoretical, average grain sizes ranging from 3.0 to 12.0 microns, and average pore sizes ranging from 1.5 to 4.0 microns. Velocity correlated with specimen bulk density irrespective of specimen average grain size, average pore size, and average pore orientation. The attenuation coefficient was found to be sensitive to both density and average pore size variations, but was not affected by large differences in average grain size.

Baaklini, George Y.↗

NASA NTRS1985

Characterization of solid particle erosion resistance of ductile metals based on their properties

This paper presents experimental results pertaining to spherical glass bead and angular crushed glass particle impingement. A concept of energy absorption to explain the failure of material is proposed and is correlated with the erosion characteristics of several pure metals. Analyses of extensive erosion data indicate that the properties - surface energy, specific melting energy, strain energy, melting point, bulk modulus, hardness, atomic volume - and the product of the parameters - linear coefficient of thermal expansion x bulk modulus x temperature rise required for melting, and ultimate resilience x hardness - exhibit the best correlations. The properties of surface energy and atomic volume are suggested for the first time for correlation purposes and are found to correlate well with erosion rates at different angles of impingement. It further appears that both energy and thermal properties contribute to the total erosion.

Rao, P. V.↗

NASA NTRS2019

EARLINET Evaluation of the CATS L2 Aerosol Backscatter Coefficient Product

We present the evaluation activity of the European Aerosol Research Lidar Network (EARLINET) for the quantitative assessment of the Level 2 aerosol backscatter coefficient product derived by the Cloud-Aerosol Transport System (CATS) onboard the International Space Station (ISS). The study employs correlative CATS and EARLINET backscatter measurements within 50km distance between the ground station and the ISS overpass and as close in time as possible, typically within 90min, from February 2015 to September 2016. The results demonstrate the good agreement of CATS Level 2 backscatter coefficient and EARLINET. Three ISS overpasses close to the EARLINET stations of Leipzig-Germany, Ã‰vora-Portugal and Dushanbe-Tajikistan are analysed here to demonstrate the performance of CATS lidar system under different conditions. The results show that under cloud-free, relative homogeneous aerosol conditions CATS is in good agreement with EARLINET, independently of daytime/nighttime conditions. CATS low negative biases, partially attributed to the deficiency of lidar systems to detect tenuous aerosol layers of backscatter signal below the minimum detection thresholds, may lead to systematic deviations and slight underestimations of the total Aerosol Optical Depth (AOD) in climate studies. In addition, CATS misclassification of aerosol layers as clouds, and vice versa, in cases of coexistent and/or adjacent aerosol and cloud features, may lead to non-representative, unrealistic and cloud contaminated aerosol profiles. The distributions of backscatter coefficient biases show the relatively good agreement between the CATS and EARLINET measurements, although on average underestimations are observed, 22.3% during daytime and 6.1% during nighttime.

EARLINET/CATS evaluation↗

NASA NTRS1993

Application of neural network to remote sensing of soil moisture using theoretical polarimetric backscattering coefficients

This paper investigates the potential application of neural network to inversion of soil moisture using polarimetric remote sensing data. The neural network used for the inversion of soil parameters is multi-layer perceptron trained with the back-propagation algorithm. The training data include the polarimetric backscattering coefficients obtained from theoretical surface scattering models together with an assumed nominal range of soil parameters which are comprised of the soil permittivity and surface roughness parameters. Soil permittivity is calculated from the soil moisture and the assumed soil texture based on an empirical formula at C-, L-, and P-bands. The rough surface parameters for the soil surface, which is described by the Gaussian random process, are the root-mean-square (rms) height and correlation length. For the rough surface scattering, small perturbation method is used for the L-band frequency, and Kirchhoff approximation is used for the C-band frequency to obtain the corresponding backscattering coefficients. During the training, the backscattering coefficients are the inputs to the neural net and the output from the net are compared with the desired soil parameters to adjust the interconnecting weights. The process is repeated for each input-output data entry and then for the entire training data until convergence is reached. After training, the backscattering coefficients are applied to the trained neural net to retrieve the soil parameters which are compared with the desired soil parameters to verify the effectiveness of this technique. Several cases are examined. First, for simplicity, the correlation length and rms height of the soil surface are fixed while soil moisture is varied. Soil moisture obtained using the neural networks with either L-band or C-band backscattering coefficients for the HH and VV polarizations as inputs is in good agreement with the desired soil moisture. The neural net output matches the desired output for the soil moisture range of 16 to 60 percent for the C-band case. The next case investigated is to vary both soil moisture and rms height while keeping the correlation length fixed. For this case, C-band backscattering coefficients are not sufficient for retrieving two parameters because the Kirchhoff approximation gives the same HH and VV backscattering coefficients. Therefore, the backscattering coefficients at two different frequency bands are necessary to find both the soil moisture and rms height. Finally, the neural nets are also applied to simultaneously invert soil moisture, rms height, and correlation length. Overall, the soil moisture retrieved from the neural network agrees very well with the desired soil moisture. This suggests that the neural network shows potential for retrieval of soil parameters from remote sensing data.

Wang, L.↗