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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Satellite-image-derived velocity field of an Antarctic ice stream

The surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery. Variations of ice velocity are spatially related to surface undulations, and transverse velocity variations of up to 30 percent occur. Such large variations negate the concept of plug flow and call into question earlier mass-balance calculations for this and other ice streams where sparse velocity data were used. The coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross-correlation of image windows provide significant improvements in the use of satellite imagery for ice-flow determination.

Bindschadler, R. A.↗
NASA NTRS1991

A light synthesis study of W Ursae Majoris

A common set of Roche model parameters produces an accurate fit to I, V, and B data for W Ursae Majoris. The R data are defective. Two pairs of cool photospheric starspots are adopted in producing the fit. The model also adopts the cross-correlation radial velocity obtained by McLean and satisfactorily eliminates evidence, cited in the literature, for a third body in the system. Changing starspot longitudes, while maintaining fixed angular diameter, latitude, and temperature contrast from the adjacent photosphere, can simulate all of the types of light curve instability recorded in historical W Ursae Majoris light curves. Although the theoretical curve accurately fits primary minimum in U, the theoretical curve is too shallow at secondary minimum. A hot secondary explanation of W-type light curves, rather than starspots on an otherwise barotropic photosphere is argued.

Linnell, Albert P.↗
NASA NTRS1990

Three-dimensional random vibration testing definition and simulation

An approach is presented for the definition of 3D random vibration test requirements for multiaxial shaker systems. In particular, it is shown that, by utilizing coherence functions for cross-correlation effects, test requirements can be defined in a simple way and provide a more realistic environmental simulation. The method is applicable to the simulation of all field environments and can be similarly employed to develop laboratory test requirements based on field data. Example problems are presented to demonstrate the approach.

Chang, Kurng Y.↗
NASA NTRS1991

Gas chromatographic concepts for the analysis of planetary atmospheres

Over the last few years, new gas chromatographic (GC) concepts were developed for use on board spacecraft or any other restricted environments for determining the chemical composition of the atmosphere and surface material of various planetary bodies. Future NASA Missions include an entry probe that will be sent to Titan and various spacecraft that will land on Mars. In order to be able to properly respond to the mission science requirements and physical restrictions imposed on the instruments by these missions, GC analytical techniques are being developed. Some of these techniques include hardware and mathematical techniques that will improve GC sensitivity and increase the sampling rate of a GC descending through a planetary atmosphere. The technique of Multiplex Gas Chromatography (MGC) is an example of a technique that was studied in a simulated Titan atmosphere. In such an environment, the atmospheric pressure at instrument deployment is estimated to be a few torr. Thus, at such pressures, the small amount of sample that is acquired might not be enough to satisfy the detection requirements of the gas chromatograph. In MGC, many samples are pseudo-randomly introduced to the chromatograph without regard to elution of preceding components. The resulting data is then reduced using mathematical techniques such as cross-correlation of Fourier Transforms. Advantages realized from this technique include: improvement in detection limits of several orders of magnitude and increase in the number of analyses that can be conducted in a given period of time. Results proving the application of MGC at very low pressures emulating the same atmospheric pressures that a Titan Probe will encounter when the instruments are deployed are presented. The sample used contained hydrocarbons that are expected to be found in Titan's atmosphere. In addition, a new selective modulator was developed to monitor water under Martian atmospheric conditions. Since this modulator is selective only to water, the need for a GC column is eliminated. This results in further simplification of the instrument.

Valentin, J. R.↗
NASA NTRS1990

Total-sky and clear-sky variability of outgoing longwave radiation and shortwave radiation and its relation to cloud fluctuation statistics

Correlation statistics are used to investigate some of the characteristic temporal and spatial scales of the day-to-day changes in cloudiness which tend to dominate the variance of outgoing LW radiation and SW radiation fields. The temporal decorrelation time of the radiation field as measured by the lag time required for the autocorrelation of a region to fall to 0.4 is about 12 hours in the midlatitude storm track. Decorrelation time approaches one to two days when the averaging area of the region is increased significantly. Decorrelation times are also longer in the equatorial and tropical regions. The short decorrelation times are a manifestation of the creation, breakup, and movement of cloud systems. Cross-correlation analysis of the radiation field in the midlatitude storm track region and the subtropical dry zone shows advection speeds that range from about 25 m/sec in the storm tracks to about 8 m/sec in the subtropical dry zone.

Bess, T. D.↗
NASA NTRS1991

Object enhanced optical correlation

A major drawback of optical correlator systems is the poor quality of correlation signals. Background noise is one of the many sources of false correlation peaks. However, by reconstructing an input scene with the object's amplitude function, an object-enhanced scene - used as input to the optical correlators - (with respect to background) can be obtained. Thus, the optical correlation of this enhanced image improves the signal-to-noise ratio in the correlation image. Furthermore, construction of a filter plane mask that permits simultaneous scene enhancement and cross-correlation operations is described. Experimental results demonstrate the practicality of this approach.

Scholl, Marija S.↗
NASA NTRS1991

Spectroscopic binary orbits from ultraviolet radial velocities. VIII - LZ Cephei (HD 209481)

We present a study of the double-lined spectroscopic binary LZ Cep based on high-resolution IUE spectra. We determine the radial velocities by using a cross-correlation technique incorporating profile fitting; this allows measurements of velocity separations down to unusually small values. The final velocity curve has a small but significant eccentricity. By considering other constraints, we construct a model for the system, which correctly predicts the light curve; in the model, the secondary fills its critical equipotential lobe. The secondary is conspicuously overluminous for its mass, and must have reached its present configuration following a phase of case A mass transfer.

Howarth, Ian D.↗
NASA NTRS1957

Near Noise Field of a Jet-Engine Exhaust

Aircraft structures located in the near noise field of a jet engine are subjected to extremely high fluctuating pressures that may cause structural fatigue. Studies of such structures have been limited by lack of knowledge of the loadings involved. The acoustic near field produced by the exhaust of a stationary turbojet engine having a high pressure ratio was measured for a single operating condition without burning. The maximum overall sound pressure without afterburning was found to be about 42 pounds per square foot along the jet boundary in the region immediately downstream of the jet-nozzle exit. With afterburning maximum sound pressure was increased by 50 percent. The sound pressures without afterburning were obtained on a constant percentage band width basis in the frequency range from 350 to 700 cps. Cross-correlation measurements with microphones were made for a range of jet velocities at locations along the jet and at a distance from the jet. In general, little change in the correlation curves was found as a function of jet velocity or frequency-band width.

Howes, Walton L↗
NASA NTRS1986

An experimental investigation of wing tip turbulence with applications to aerosound

Wind tunnel tests were performed to measure the turbulence characteristics of flow in the wing tip region of a blunt tipped NACA 0012 airfoil at angles of attack of 16, 12 and 6 deg and flow speeds of 75, 55, and 35 m/s. Reynolds numbers based on the chord length ranged from 1.8 x 10(exp6) to 3.8 x 10(exp 6). Hot wire measurements were made at an angle of attack of 12 deg and U(infinity) = 55 ms. These indicate fluctuation velocities on the order of 0.13 U(infinity) in the tip region. Surface pressure spectra are presented for alpha = 12 deg and 16 deg; surface-pressure cross-correlations are presented for alpha = 16 deg. These suggest the presence of a well organized turbulence structure with a peak Strouhal number 0.8 to 1.1 based on the wing thickness. High frequency turbulence of lesser intensity was measured at positions near the primary tip vortex on the upper wing surface. A separation region with a spectral peak of St approximately equal to 0.4 was recorded at alpha = 16 deg for the transducer located on the low pressure side of the wing nearest the trailing edge. Surface-surface cross correlations display a double, echo like structure. Near-far field correlations indicate that the well ordered tip turbulence and the separation region on the upper surface both radiate significant levels of far field sound. The use of cross correlation techniques in the wind tunnel has permitted treatment of radiated sound levels which are 25 and more dB below tunnel background levels.

Mcinerny, S. A.↗
NASA NTRS1961

Sound Pressures and Correlations of Noise on the Fuselage of a Jet Aircraft in Flight

Tests were conducted at altitudes of 10,000, 20,000, and 30,000 feet at speeds of Mach 0.4, 0.6, and O.8. It was found that the sound pressure levels on the aft fuselage of a jet aircraft in flight can be estimated using an equation involving the true airspeed and the free air density. The cross-correlation coefficient over a spacing of 2.5 feet was generalized with Strouhal number. The spectrum of the noise in flight is comparatively flat up to 10,000 cycles per second.

Shattuck, Russell D.↗
NASA NTRS1989

Psychology of computer use: IX. A menu of self-administered microcomputer-based neurotoxicology tests

This study examined the feasibility of repeated self-administration of a newly developed battery of mental acuity tests which may have application in screening for fitness-for-duty or for persons who may be exposed to environmental stress, toxic agents, or disease. 16 subjects self-administered 18 microcomputer-based tests (13 new, 5 "core"), without proctors, over 10 sessions. The hardware performed well throughout the study and the tests appeared to be easily self-administered. Stabilities and reliabilities of the tests from the "core" battery were comparable to those obtained previously under more controlled experimental conditions. Eight of the new tests exceeded minimum criteria for metric and practical requirements and can be recommended as additions to the menu. Although the average retest reliability was high, cross-correlations between tests were low, implying factorial diversity. The menu can be used to form batteries with flexible total testing time which are likely to tap different mental processes and functions.

NASA Discipline Neuroscience↗
DOE OSTI2025

Measurement of Parity-Violating Modes of the Dark Energy Spectroscopic Instrument (DESI) Year 1 Luminous Red Galaxies' 4-Point Correlation Function

Here we report the first measurement of the parity-violating (PV) 4-Point Correlation Function (4PCF) of the Dark Energy Spectroscopic Instrument's Year 1 Luminous Red Galaxy (DESI Y1 LRG) sample, motivated by the potential detection of the PV 4PCF in the Sloan Digital Sky Survey Baryon Oscillation Spectroscopic Survey (SDSS BOSS) galaxies. In our auto-correlation ("auto") analysis, we find a statistically significant excess of the PV signal compared to mocks without any PV, at 4-10$σ$ depending on details of the analysis. This could arise either from genuine PV or from an underestimation of the variance in the mocks; it is unlikely to arise, at the signal level, from a systematic. We then cross-correlate ("cross") the putative PV signal between different, independent patches of sky, and there find no detection of parity violation. The two measurements are in significant tension: while the cross has somewhat larger error bars than the auto, this is not sufficient to explain the discrepancy. We thus present the current work as an intriguing addition to the PV work on BOSS and as motivation for exploring further the relationship between the auto and cross PV 4PCF analyses.

Slepian, Zachary [Florida U.]↗
DOE OSTI2025

DECADE+DES Y3 Weak Lensing Mass Map: A 13,000 deg$^2$ View of Cosmic Structure from 270 Million Galaxies

We present the largest galaxy weak lensing mass map of the late-time Universe, reconstructed from 270 million galaxies in the DECADE and DES Year 3 datasets, covering 13,000 square degrees. We validate the map through systematic tests against observational conditions (depth, seeing, etc.), finding the map is statistically consistent with no contamination. The large area covered by the mass map makes it a well-suited tool for cosmological analyses, cross-correlation studies and the identification of large-scale structure features. We demonstrate its potential by detecting cosmic filaments directly from the mass map for the first time and validating them through their association with galaxy clusters selected using the Sunyaev-Zeldovich effect from Planck and ACT DR6.

Gatti, M. [Chicago U., KICP] (ORCID:00000001613487↗
DOE OSTI2025

Direct Measurement of Galaxy Assembly Bias using DESI DR1 Data

We report the first direct measurement of galaxy assembly bias, a critical systematic in cosmology, from the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey. We introduce a novel, cosmology-independent method to measure the halo occupation distribution (HOD) by combining a state-of-the-art group catalog with weak gravitational lensing. For groups binned by total luminosity, we determine the galaxy occupation number $N_{\rm gal}$ from group-galaxy cross-correlations, while weak lensing constrains the average halo mass $M_h$. Applying this to a volume-limited sample at $z{\in}[0.05,0.2]$, we measure the dependence of HOD, $N_{\rm gal}(M_h)$, on large-scale overdensity $δ_{g}$. Focusing on the satellite galaxies, we find an assembly bias parameter of $Q_{\rm sat}{=}0.05{\pm}0.14$, a result consistent with zero and in tension with many empirical galaxy formation models. Our method provides a robust approach for characterizing galaxy assembly bias to achieve precision cosmology with DESI and future Stage-V surveys.

Shao, Zhiwei [Shanghai Jiaotong U.; Shanghai Jiao ↗
DOE OSTI2025

Dark Energy Survey Year 6 Results: Redshift Calibration of the Weak Lensing Source Galaxies

Determining the distribution of redshifts for galaxies in wide-field photometric surveys is essential for robust cosmological studies of weak gravitational lensing. We present the methodology, calibrated redshift distributions, and uncertainties of the final Dark Energy Survey Year 6 (Y6) weak lensing galaxy data, divided into four redshift bins centered at $\langle z \rangle = [0.414, 0.538, 0.846, 1.157]$. We combine independent information from two methods on the full shape of redshift distributions: optical and near-infrared photometry within an improved Self-Organizing Map $p(z)$ (SOMPZ) framework, and cross-correlations with spectroscopic galaxy clustering measurements (WZ), which we demonstrate to be consistent both in terms of the redshift calibration itself and in terms of resulting cosmological constraints within 0.1$σ$. We describe the process used to produce an ensemble of redshift distributions that account for several known sources of uncertainty. Among these, imperfection in the calibration sample due to the lack of faint, representative spectra is the dominant factor. The final uncertainty on mean redshift in each bin is $σ_{\langle z\rangle} = [0.012, 0.008,0.009, 0.024]$. We ensure the robustness of the redshift distributions by leveraging new image simulations and a cross-check with galaxy shape information via the shear ratio (SR) method.

Yin, B. [Duke U.] (ORCID:0009000656049980)↗
DOE OSTI2025

Joint cosmological fits to DESI-DR1 full-shape clustering and weak gravitational lensing in configuration space

We present a joint $3\times2$-pt cosmological analysis of auto- and cross-correlations between the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1) Bright Galaxy Survey (BGS) and Luminous Red Galaxy (LRG) samples and overlapping shear measurements from the KiDS-1000, DES-Y3 and HSC-Y3 weak lensing surveys. We perform our analysis in configuration space and, in addition to the cosmic shear correlation functions for each weak lensing dataset, we fit the tangential shear of the weak lensing source galaxies around DESI lens galaxies. Finally, we make use of the anisotropic BGS and LRG clustering information by fitting the full shape of the two-point correlation function multipoles measured over the full DESI-DR1 footprint, presenting the first full-shape analysis of DESI measurements in configuration space. We find that the addition of weak lensing information serves to improve, with respect to the clustering-only case, the measurements of the power spectrum amplitude parameters $\ln(10^{10}A_{\rm{s}})$ and $σ_{12}$ by $15\%$ and $36\%$, respectively. It also improves measurements of the linear bias of the lens galaxies by $15-20\%$, depending on the tracer. Our results show excellent consistency, regardless of the weak lensing survey considered, and are furthermore consistent with a companion analysis that fits $3\times2$-pt correlations including DESI projected clustering measurements, as well as the results published by the weak lensing collaborations themselves. Our measured values for weak lensing amplitude are $S_{8}^{\mathrm{DESI\times HSC}}=0.787\pm0.020$, $S_{8}^{\mathrm{DESI\times DES}}=0.791\pm0.016$, $S_{8}^{\mathrm{DESI\times KiDS}}=0.771\pm0.017$, which are $1.9σ-2.9σ$ below the $S_8$ value preferred by Planck. Finally, our clustering-only results are in good agreement with the Fourier space full-shape analysis of all DESI tracers.

Semenaite, A. [Swinburne U., Ctr. Astrophys. Super↗
DOE OSTI2025

Clustering redshift distribution calibration of weak lensing surveys using the DESI-DR1 spectroscopic dataset

We estimate the source redshift distribution of current weak lensing surveys by applying the clustering-based redshift calibration technique, using the galaxy redshift sample provided by the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1). We cross-correlate the Bright Galaxy Survey (BGS), Luminous Red Galaxies (LRGs) and Emission Line Galaxies (ELGs) from DESI, within the redshift range $0.1 < z < 1.6$, with overlapping tomographic source samples from the Dark Energy Survey (DES), Kilo-Degree Survey (KiDS), and Hyper Suprime-Cam (HSC) survey. Using realistic mock catalogues, we test the stability of the clustering-redshift signal to fitting scale, reference-sample choice, and the evolution of source galaxy bias, and we explicitly model and marginalise over magnification contributions, which become non-negligible at $z \gtrsim 1$ due to the depth of the DESI ELG sample. We then compare the resulting bias-weighted redshift distributions to those calibrated using self-organising map (SOM) techniques, finding agreement within uncertainties for all surveys and tomographic bins. Our results demonstrate that clustering redshifts enabled by DESI's unprecedented spectroscopic sample provides a robust, complementary, and independent constraint capable of reducing one of the dominant systematic uncertainties in weak lensing cosmology.

Ruggeri, R. [Queensland U.]↗
DOE OSTI2026

Dark Energy Survey Year 6 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing

We present cosmology results combining galaxy clustering and weak gravitational lensing measured in the full six years (Y6) of observations by the Dark Energy Survey (DES) covering $\sim$5000 deg$^2$. We perform a large-scale structure analysis using three two-point correlation functions (3$\times$2pt): (i) cosmic shear from 140 million source galaxy shapes, (ii) galaxy clustering of 9 million lens galaxy positions, and (iii) galaxy-galaxy lensing from their cross-correlation. We model the data in flat $Λ$CDM and $w$CDM cosmologies. The combined analysis yields $S_8\equiv σ_8 (Ω_{\rm m}/0.3)^{0.5} = 0.789^{+0.012}_{-0.012}$ and matter density $Ω_{\rm m} = 0.333^{+0.023}_{-0.028}$ in $Λ$CDM (68% CL), where $σ_8$ is the clustering amplitude. These constraints show a (full-space) parameter difference of 1.8$σ$ from a combination of cosmic microwave background (CMB) primary anisotropy datasets from Planck 2018, ACT-DR6, and SPT-3G DR1. Projected only into $S_8$ the difference is $2.6σ$. In $w$CDM the Y6 3$\times$2pt results yield $S_8 = 0.782^{+0.021}_{-0.020}$, $Ω_{\rm m} = 0.325^{+0.032}_{-0.035}$, and dark energy equation-of-state parameter $w = -1.12^{+0.26}_{-0.20}$. For the first time, we combine all DES dark-energy probes: 3$\times$2pt, SNe Ia, BAO and Clusters. In $Λ$CDM this combination yields a $2.8σ$ parameter difference from the CMB. When combining DES 3$\times$2pt with other low-redshift datasets (DESI DR2 BAO, DES SNe Ia, SPT clusters), we find a 2.3$σ$ parameter difference with CMB. A joint fit of Y6 3$\times$2pt, CMB, and those low-redshift datasets produces the tightest $Λ$CDM constraints to date: $S_8 = 0.806^{+0.006}_{-0.007}$, $Ω_{\rm m} = 0.302^{+0.003}_{-0.003}$, $h = 0.683^{+0.003}_{-0.002}$, and $\sum m_ν< 0.14$ eV (95% CL). In $w$CDM, this combination yields $w = -0.981^{+0.021}_{-0.022}$.

Abbott, T. M.C. [Cerro-Tololo InterAmerican Obs.]↗