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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

A practical computational method for the anisotropic redshift-space three-point correlation function

Here, we present an algorithm enabling computation of the anisotropic redshift-space galaxy threepoint correlation function ( 3 PCF) scaling as N 2 , with N the number of galaxies. Our previous work showed how to compute the isotropic 3 PCF with this scaling by expanding the radially binned density field around each galaxy in the survey into spherical harmonics and combining these coefficients to form multipole moments. The N 2 scaling occurred because this approach never explicitly required the relative angle between a galaxy pair about the primary galaxy. Here, we generalize this work, demonstrating that in the presence of azimuthally symmetric anisotropy produced by redshift-space distortions (RSD), the 3 PCF can be described by two triangle side lengths, two independent total angular momenta, and a spin. This basis for the anisotropic 3 PCF allows its computation with negligible additional work over the isotropic 3 PCF. We also present the covariance matrix of the anisotropic 3 PCF measured in this basis. Our algorithm tracks the full 5 D redshift-space 3 PCF, uses an accurate line of sight to each triplet, is exact in angle, and easily handles edge correction. It will enable use of the anisotropic large-scale 3 PCF as a probe of RSD in current and upcoming large-scale redshift surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Collaboration 51 Correlation Function Analysis Suite (c51_corr_analysis) v0.1.0

This is a data analysis package designed for analyzing correlation functions generated with lattice QCD calculations. The purpose is to make a centralized software suite for use by all members of my collaboration, so that various members can spend less time developing their own analysis codes, and more time extracting the interesting physics from our calculations. There are also 3 independent collaborations that have expressed interest in using this code, so there is some expectation it will be used in the broader international lattice QCD community.

Walker-Loud, Andre↗
DOE OSTI2026

First Detection of the Baryon Acoustic Oscillation (BAO) Feature in the 3-Point Correlation Function of DESI DR1 Luminous Red Galaxies

We present the first detection of the 3-Point Correlation Function (3PCF) Baryon Acoustic Oscillation (BAO) signal from the DESI Data Release 1 (DR1) sample of Luminous Red Galaxies (LRGs), which contains over 2.1 million galaxies. Our analysis is based on a tree-level redshift-space bispectrum template, which is then transformed to position space using the Fast Fourier Transform on Logarithmic scales (FFTLog) algorithm. We detect the BAO feature with a significance of approximately $8.1σ$ using the EZmock covariance matrix and $8.5σ$ using the analytical covariance matrix, for the full LRG redshift range ($0.4

Kamalinejad, Farshad [Florida U.] (ORCID:000000017↗
DOE OSTI2015

Statistics of time delay and scattering correlation functions in chaotic systems. I. Random matrix theory

We consider the statistics of time delay in a chaotic cavity having M open channels, in the absence of time-reversal invariance. In the random matrix theory approach, we compute the average value of polynomial functions of the time delay matrix Q = − iħS{sup †}dS/dE, where S is the scattering matrix. Our results do not assume M to be large. In a companion paper, we develop a semiclassical approximation to S-matrix correlation functions, from which the statistics of Q can also be derived. Together, these papers contribute to establishing the conjectured equivalence between the random matrix and the semiclassical approaches.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Baryon acoustic oscillations from the complete SDSS-III Lyα-quasar cross-correlation function at z = 2.4

We present a measurement of baryon acoustic oscillations (BAO) in the cross-correlation of quasars with the Lyα-forest flux-transmission at a mean redshift z = 2.40. The measurement uses the complete SDSS-III data sample: 168,889 forests and 234,367 quasars from the SDSS Data Release DR12. In addition to the statistical improvement on our previous study using DR11, we have implemented numerous improvements at the analysis level allowing a more accurate measurement of this cross-correlation. We also developed the first simulations of the cross-correlation allowing us to test different aspects of our data analysis and to search for potential systematic errors in the determination of the BAO peak position. We measure the two ratios D H (z = 2.40)=r d = 9.01 ± 0.36 and D M (z = 2.40)=r d = 35.7 ±1.7, where the errors include marginalization over the non-linear velocity of quasars and the metal - quasar cross-correlation contribution, among other effects. These results are within 1.8σ of the prediction of the flat-ΛCDM model describing the observed CMB anisotropies.We combine this study with the Lyα-forest auto-correlation function (Bautista et al. 2017), yielding D H (z = 2.40)=r d = 8.94 ± 0.22 and D M (z = 2.40)=r d = 36.6 ± 1.2, within 2.3σ of the same flat-ΛCDM model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Galaxy Clustering in the Mira-Titan Universe. I. Emulators for the Redshift Space Galaxy Correlation Function and Galaxy–Galaxy Lensing

Abstract We construct accurate emulators for the projected and redshift space galaxy correlation functions and excess surface density as measured by galaxy–galaxy lensing, based on halo occupation distribution modeling. Using the complete Mira-Titan suite of 111 N -body simulations, our emulators vary over eight cosmological parameters and include the effects of neutrino mass and dynamical dark energy. We demonstrate that our emulators are sufficiently accurate for the analysis of the Baryon Oscillation Spectroscopic Survey DR12 CMASS galaxy sample over the range 0.5 ≤ r ≤ 50 h −1 Mpc. Furthermore, we show that our emulators are capable of recovering unbiased cosmological constraints from realistic mock catalogs over the same range. Our mock catalog tests show the efficacy of combining small-scale galaxy–galaxy lensing with redshift space clustering and that we can constrain the growth rate and σ 8 to 7% and 4.5%, respectively, for a CMASS-like sample using only the measurements covered by our emulator. With the inclusion of a cosmic microwave background prior on H 0 , this reduces to a 2% measurement of the growth rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Measurement of neutron and gamma-ray cross-correlation functions with 4 He detectors

For the first time, the neutron and gamma-ray time-dependent cross-correlation distributions from spontaneous fission and (α, n) neutron sources are measured with the 4 He fast neutron detectors. The pulse shape discrimination technique based on charge comparison is utilized to discriminate between neutrons and gamma-rays in the identification of the four possible correlated pairs: (γ, γ), (n, n), (γ, n), and (n, n). Both total and individual cross-correlation functions are obtained, and their shapes can be easily distinguished among different neutron sources. The (n, n) and (γ, n) correlations are selectively analyzed and the peak position of the (n, n) and (γ, n) pairs shows a linear correlation with source-detector distance. Here, the measurements illustrate the feasibility of using 4 He detectors to identify nuclear materials and their geometrical configurations, as well as other applications in nuclear nonproliferation and safeguards. In particular, the (n, n) correlated data can be very clearly assayed even in the presence of significant gamma fields without the use of shielding.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

An Exchange-Correlation Functional Capturing Bulk Surface and Confinement Physics

Due to its balance of accuracy and computational cost, density functional theory has become the method of choice for computing the electronic structure and related properties of materials. However, present-day semilocal approximations to the exchange-correlation energy of density functional theory break down for materials containing d and f electrons. In this report we summarize our progress in addressing this issue. We describe the construction of the BSC exchange-correlation functional within the subsystem functional formalism which enables us to capture bulk, surface, and confinement physics with a single exchange-correlation functional. We report on the initial assessment of this functional within the jellium surface system and demonstrate that the BSC functional captures the confinement physics more accurately than standard semilocal exchange-correlation functionals. We conclude by outlining our future research objectives which focus on refining the functional form of the BSC functional and achieving significantly more accurate energetics of materials containing f and d electrons than existing semilocal functionals.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Analytic representations of bath correlation functions for ohmic and superohmic spectral densities using simple poles

We present a scheme to express a bath correlation function (BCF) corresponding to a given spectral density (SD) as a sum of damped harmonic oscillations. Such a representation is needed, for example, in many open quantum system approaches. To this end we introduce a class of fit functions that enables us to model ohmic as well as superohmic behavior. We show that these functions allow for an analytic calculation of the BCF using pole expansions of the temperature dependent hyperbolic cotangent. We demonstrate how to use these functions to fit spectral densities exemplarily for cases encountered in the description of photosynthetic light harvesting complexes. Finally, we compare absorption spectra obtained for different fits with exact spectra and show that it is crucial to take properly into account the behavior at small frequencies when fitting a given SD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Modelling the large-scale redshift-space 3-point correlation function of galaxies

We present a configuration-space model of the large-scale galaxy 3-point correlation function (3PCF) based on leading-order perturbation theory and including redshift-space distortions (RSD). This model should be useful in extracting distance-scale information from the 3PCF via the baryon acoustic oscillation method. We include the first redshift-space treatment of biasing by the baryon-dark matter relative velocity. Overall, on large scales the effect of RSD is primarily a renormalization of the 3PCF that is roughly independent of both physical scale and triangle opening angle; for our adopted Ωm and bias values, the rescaling is a factor of ~1.8. We also present an efficient scheme for computing 3PCF predictions from our model, important for allowing fast exploration of the space of cosmological parameters in future analyses.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Mapping the real-space distributions of galaxies in SDSS DR7. I. Two-point correlation functions

Using a method to correct redshift-space distortion (RSD) for individual galaxies, we mapped the real-space distributions of galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We use an ensemble of mock catalogs to demonstrate the reliability of our method. Here, in the first paper in a series, we focus mainly on the two-point correlation function (2PCF) of galaxies. Overall the 2PCF measured in the reconstructed real space for galaxies brighter than {sup 0.1}M{sub r}−5logh=−19.0 agrees with the direct measurement to an accuracy better than the measurement error due to cosmic variance, if the reconstruction uses the correct cosmology. Applying the method to the SDSS DR7, we construct a real-space version of the main galaxy catalog, which contains 396,068 galaxies in the North Galactic Cap with redshifts in the range 0.01 ≤ z ≤ 0.12. The Sloan Great Wall, the largest known structure in the nearby universe, is not as dominant an overdense structure as it appears to be in redshift space. We measure the 2PCFs in reconstructed real space for galaxies of different luminosities and colors. All of them show clear deviations from single power-law forms, and reveal clear transitions from one-halo to two-halo terms. A comparison with the corresponding 2PCFs in redshift space nicely demonstrates how RSDs boost the clustering power on large scales (by about 40%–50% at scales ∼10 h{sup −1} Mpc) and suppress it on small scales (by about 70%–80% on a scale of 0.3 h{sup −1} Mpc).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

GUNDAM: a toolkit for fast spatial correlation functions in galaxy surveys

ABSTRACT We describe the capabilities of a new software package to calculate two-point correlation functions (2PCFs) of large galaxy samples. The code can efficiently estimate 3D/projected/angular 2PCFs with a variety of statistical estimators and bootstrap errors, and is intended to provide a complete framework (including calculation, storage, manipulation, and plotting) to perform this type of spatial analysis with large redshift surveys. Gundam implements a very fast skip list/linked list algorithm that efficiently counts galaxy pairs and avoids the computation of unnecessary distances. It is several orders of magnitude faster than a naive pair counter, and matches or even surpass other advanced algorithms. The implementation is also embarrassingly parallel, making full use of multicore processors or large computational clusters when available. The software is designed to be flexible, user friendly and easily extensible, integrating optimized, well-tested packages already available in the astronomy community. Out of the box, it already provides advanced features such as custom weighting schemes, fibre collision corrections and 2D correlations. Gundam will ultimately provide an efficient toolkit to analyse the large-scale structure ‘buried’ in upcoming extremely large data sets generated by future surveys.

Donoso, E.↗
DOE OSTI2025

Nanoscale Phase Identification Using Two-Dimensional Pair Correlation Functions: A Case Study on Hafnium Oxide

Accurate identification of local phases in nanocrystalline materials is essential for understanding their functional properties, but it remains a significant challenge for polymorphic materials to locally differentiate them at nanoscale. This challenge is further compounded in polycrystalline materials with randomly oriented grains and the coexistence of multiple phases. In this report, we present a methodology for phase and orientation identification at the nanoscale by leveraging vector pair correlation functions extracted from atomically resolved scanning transmission electron microscopy (STEM) images. We demonstrate the accuracy of the methodology on both simulated and experimental data from HfO 2 -based films, a material that exhibits multiple coexisting phases in films with thicknesses ranging from 5 to 20 nm. While demonstrated on HfO 2 films, the methodology can be extended to other polymorphic nanocrystalline systems with complex phase coexistence.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Self-consistent redshift estimation using correlation functions without a spectroscopic reference sample

ABSTRACT We present a new method to estimate redshift distributions and galaxy-dark matter bias parameters using correlation functions in a fully data driven and self-consistent manner. Unlike other machine learning, template, or correlation redshift methods, this approach does not require a reference sample with known redshifts. By measuring the projected cross- and auto-correlations of different galaxy sub-samples, e.g. as chosen by simple cells in colour–magnitude space, we are able to estimate the galaxy-dark matter bias model parameters, and the shape of the redshift distributions of each sub-sample. This method fully marginalizes over a flexible parametrization of the redshift distribution and galaxy-dark matter bias parameters of sub-samples of galaxies, and thus provides a general Bayesian framework to incorporate redshift uncertainty into the cosmological analysis in a data-driven, consistent, and reproducible manner. This result is improved by an order of magnitude by including cross-correlations with the cosmic microwave background and with galaxy–galaxy lensing. We showcase how this method could be applied to real galaxies. By using idealized data vectors, in which all galaxy-dark matter model parameters and redshift distributions are known, this method is demonstrated to recover unbiased estimates on important quantities, such as the offset Δz between the mean of the true and estimated redshift distribution and the 68 per cent, 95 per cent, and 99.5 per cent widths of the redshift distribution to an accuracy required by current and future surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Properties of Noise Cross-Correlation Functions Obtained from a Distributed Acoustic Sensing Array at Garner Valley, California

A field test that was conducted at Garner Valley, California, on 11 and 12 September 2013 using distributed acoustic sensing (DAS) to sense ground vibrations provided a continuous overnight record of ambient noise. Furthermore, the energy of ambient noise was concentrated between 5 and 25 Hz, which falls into the typical traffic noise frequency band. A standard procedure (Bensen et al., 2007) was adopted to calculate noise cross-correlation functions (NCFs) for 1-min intervals. The 1-min-long NCFs were stacked using the time–frequency domain phase-weighted-stacking method, which significantly improves signal quality. The obtained NCFs were asymmetrical, which was a result of the nonuniform distributed noise sources. A precursor appeared on NCFs along one segment, which was traced to a strong localized noise source or a scatterer at a nearby road intersection. NCF for the radial component of two surface accelerometers along a DAS profile gave similar results to those from DAS channels. Here, we calculated the phase velocity dispersion from DAS NCFs using the multichannel analysis of surface waves technique, and the result agrees with active-source results. We then conclude that ambient noise sources and the high spatial sampling of DAS can provide the same subsurface information as traditional active-source methods.

58 GEOSCIENCES↗
DOE OSTI2020

The completed SDSS-IV extended baryon oscillation spectroscopic survey: geometry and growth from the anisotropic void–galaxy correlation function in the luminous red galaxy sample

ABSTRACT We present an analysis of the anisotropic redshift-space void–galaxy correlation in configuration space using the Sloan Digital Sky Survey extended Baryon Oscillation Spectroscopic Survey (eBOSS) Data Release 16 luminous red galaxy (LRG) sample. This sample consists of LRGs between redshifts 0.6 and 1.0, combined with the high redshift z > 0.6 tail of the Baryon Oscillation Spectroscopic Survey Data Release 12 CMASS sample. We use a reconstruction method to undo redshift-space distortion (RSD) effects from the galaxy field before applying a watershed void-finding algorithm to remove bias from the void selection. We then perform a joint fit to the multipole moments of the correlation function for the growth rate fσ8 and the geometrical distance ratio DM/DH, finding $f\sigma _8(z_\rm {eff})=0.356\pm 0.079$ and $D_M/D_H(z_\rm {eff})=0.868\pm 0.017$ at the effective redshift $z_\rm {eff}=0.69$ of the sample. The posterior parameter degeneracies are orthogonal to those from galaxy clustering analyses applied to the same data, and the constraint achieved on DM/DH is significantly tighter. In combination with the consensus galaxy BAO and full-shape analyses of the same sample, we obtain fσ8 = 0.447 ± 0.039, DM/rd = 17.48 ± 0.23, and DH/rd = 20.10 ± 0.34. These values are in good agreement with the ΛCDM model predictions and represent reductions in the uncertainties of $13{{\ \rm per\ cent}}$, $23{{\ \rm per\ cent}}$, and $28{{\ \rm per\ cent}}$, respectively, compared to the combined results from galaxy clustering, or an overall reduction of 55 per cent in the allowed volume of parameter space.

Nadathur, Seshadri↗
DOE OSTI2018

Summability of Connected Correlation Functions of Coupled Lattice Fields

We consider two nonindependent random fields ψ and ϕ defined on a countable set Z. For instance, Z=ℤ{sup d} or Z=ℤ{sup d}×I, where I denotes a finite set of possible “internal degrees of freedom” such as spin. We prove that, if the cumulants of ψ and ϕ enjoy a certain decay property, then all joint cumulants between ψ and ϕ are ℓ{sub 2}-summable in the precise sense described in the text. The decay assumption for the cumulants of ψ and ϕ is a restricted ℓ{sub 1} summability condition called ℓ{sub 1}-clustering property. One immediate application of the results is given by a stochastic process ψ{sub t}(x) whose state is ℓ{sub 1}-clustering at any time t: then the above estimates can be applied with ψ=ψ{sub t} and ϕ=ψ{sub 0} and we obtain uniform in t estimates for the summability of time-correlations of the field. The above clustering assumption is obviously satisfied by any ℓ{sub 1}-clustering stationary state of the process, and our original motivation for the control of the summability of time-correlations comes from a quest for a rigorous control of the Green–Kubo correlation function in such a system. A key role in the proof is played by the properties of non-Gaussian Wick polynomials and their connection to cumulants.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗