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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Systematic errors in low-latency gravitational wave parameter estimation impact electromagnetic follow-up observations

Among the most eagerly anticipated opportunities made possible by Advanced LIGO/Virgo are multimessenger observations of compact mergers. Optical counterparts may be short-lived so rapid characterization of gravitational wave (GW) events is paramount for discovering electromagnetic signatures. One way to meet the demand for rapid GW parameter estimation is to trade off accuracy for speed, using waveform models with simplified treatment of the compact objects’ spin. We report on the systematic errors in GW parameter estimation suffered when using different spin approximations to recover generic signals. Component mass measurements can be biased by >5σ using simple-precession waveforms and in excess of 20σ when non-spinning templates are employed. This suggests that electromagnetic observing campaigns should not take a strict approach to selecting which LIGO/Virgo candidates warrant follow-up observations based on low-latency mass estimates. For sky localization, we find that searched areas are up to a factor of ∼2 larger for non-spinning analyses, and are systematically larger for any of the simplified waveforms considered in our analysis. Distance biases for the non-precessing waveforms can be in excess of 100% and are largest when the spin angular momenta are in the orbital plane of the binary. We confirm that spin-aligned waveforms should be used for low-latency parameter estimation at the minimum. Including simple precession, though more computationally costly, mitigates biases except for signals with extreme precession effects. Our results shine a spotlight on the critical need for development of computationally inexpensive precessing waveforms and/or massively parallel algorithms for parameter estimation.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2011

An Examination of the Spatial Distribution of Carbon Dioxide and Systematic Errors

The industrial period and modern age is characterized by combustion of coal, oil, and natural gas for primary energy and transportation leading to rising levels of atmospheric of CO2. This increase, which is being carefully measured, has ramifications throughout the biological world. Through remote sensing, it is possible to measure how many molecules of CO2 lie in a defined column of air. However, other gases and particles are present in the atmosphere, such as aerosols and water, which make such measurements more complicated1. Understanding the detailed geometry and path length of the observation is vital to computing the concentration of CO2. Comparing these satellite readings with ground-truth data (TCCON) the systematic errors arising from these sources can be assessed. Once the error is understood, it can be scaled for in the retrieval algorithms to create a set of data, which is closer to the TCCON measurements1. Using this process, the algorithms are being developed to reduce bias, within.1% worldwide of the true value. At this stage, the accuracy is within 1%, but through correcting small errors contained in the algorithms, such as accounting for the scattering of sunlight, the desired accuracy can be achieved.

Carbon Dioxide (CO2)↗
DOE OSTI2017

Managing systematic errors in the NBSR thermal power calorimetric measurements - 214

There has been a calorimetric misbalance between the primary and secondary loops of the National Bureau of Standards Reactor (NBSR) since the installation of a set of new heat exchangers in the early 90's. The NBSR's primary and secondary process instrumentation were investigated to resolve the underlying causes. The main issue was found to be the immersion length of the thermowells, resulting in non-exemplary process measurements. Furthermore, thermal insulation on various temperature sensors was found to be degraded. Hence, the following were found to be inconsistent: the heat exchanger output temperatures, previously-used differential temperature sensors, reactor inlet sensor, and the reactor outlet temperature indications. Therefore, thermodynamic analyses using these sensor measurements were inconclusive. Secondly, the discrepancy between primary and secondary loops and the gradual inconsistency between primary side sensors went largely unnoticed. We implemented sustainable, state-of-the-art upgrades to resolve systematic errors in the NBSR reactor thermal process instrumentation. Several digital upgrades were completed, along with detailed 50.59 reviews. Redundancy, defense-in-depth, reliability, diversity and accuracy of the thermal monitoring system was established by implementing an inclusive engineering approach by analyzing the sensors as a whole system instead of individual assessments. The upgrades produced two important outcomes. First, the long-term existing calorimetric discrepancy between the primary and secondary loops was resolved. Secondly, excellent agreement was achieved within the primary process measurement instrumentation, resulting in reliable and stable thermal power assessment. We will present lessons learned performing instrumentation upgrades and our future enhancement plans in process monitoring for the NBSR reactor. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2022

Sub 20 cm -1 computational prediction of the CH bond energy – a case of systematic error in computational thermochemistry

Here, the bond dissociation energy of methylidyne, D 0 (CH), is studied using an improved version of the High-Accuracy Extrapolated ab initio Thermochemistry (HEAT) approach as well as the Feller–Peterson–Dixon (FPD) model chemistry. These calculations, which include basis sets up to nonuple (aug-cc-pCV9Z) quality, are expected to be capable of providing results substantially more accurate than the ca. 1 kJ mol -1 level that is characteristic of standard high-accuracy protocols for computational thermochemistry. The calculated 0 K CH bond energy (27 954 ± 15 cm -1 for HEAT and 27 956 ± 15 cm -1 for FPD), along with equivalent treatments of the CH ionization energy and the CH + dissociation energy (85 829 ± 15 cm -1 and 32 946 ± 15 cm -1 , respectively), were compared to the existing benchmarks from Active Thermochemical Tables (ATcT), uncovering an unexpected difference for D 0 (CH). This has prompted a detailed reexamination of the provenance of the corresponding ATcT benchmark, allowing the discovery and subsequent correction of a systematic error present in several published high-level calculations, ultimately yielding an amended ATcT benchmark for D 0 (CH). Finally, the current theoretical results were added to the ATcT Thermochemical Network, producing refined ATcT estimates of 27 957.3 ± 6.0 cm -1 for D0(CH), 32 946.7 ± 0.6 cm -1 for D 0 (CH + ), and 85 831.0 ± 6.0 cm -1 for IE(CH).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2007

Derivation and Application of a Global Albedo yielding an Optical Brightness To Physical Size Transformation Free of Systematic Errors

Orbital object data acquired via optical telescopes can play a crucial role in accurately defining the space environment. Radar systems probe the characteristics of small debris by measuring the reflected electromagnetic energy from an object of the same order of size as the wavelength of the radiation. This signal is affected by electrical conductivity of the bulk of the debris object, as well as its shape and orientation. Optical measurements use reflected solar radiation with wavelengths much smaller than the size of the objects. Just as with radar, the shape and orientation of an object are important, but we only need to consider the surface electrical properties of the debris material (i.e., the surface albedo), not the bulk electromagnetic properties. As a result, these two methods are complementary in that they measure somewhat independent physical properties to estimate the same thing, debris size. Short arc optical observations such as are typical of NASA's Liquid Mirror Telescope (LMT) give enough information to estimate an Assumed Circular Orbit (ACO) and an associated range. This information, combined with the apparent magnitude, can be used to estimate an "absolute" brightness (scaled to a fixed range and phase angle). This absolute magnitude is what is used to estimate debris size. However, the shape and surface albedo effects make the size estimates subject to systematic and random errors, such that it is impossible to ascertain the size of an individual object with any certainty. However, as has been shown with radar debris measurements, that does not preclude the ability to estimate the size distribution of a number of objects statistically. After systematic errors have been eliminated (range errors, phase function assumptions, photometry) there remains a random geometric albedo distribution that relates object size to absolute magnitude. Measurements by the LMT of a subset of tracked debris objects with sizes estimated from their radar cross sections indicate that the random variations in the albedo follow a log-normal distribution quite well. In addition, this distribution appears to be independent of object size over a considerable range in size. Note that this relation appears to hold for debris only, where the shapes and other properties are not primarily the result of human manufacture, but of random processes. With this information in hand, it now becomes possible to estimate the actual size distribution we are sampling from. We have identified two characteristics of the space debris population that make this process tractable and by extension have developed a methodology for performing the transformation.

Mulrooney, Dr. Mark K.↗
DOE OSTI2020

Physically based correction of systematic errors of Rotating Shadowband Irradiometers

Accurate measurements of direct normal, diffuse horizontal and global horizontal irradiance (DNI, DHI and GHI) are needed for meteorological studies and are essential for the solar resource assessment at potential solar power plant sites. Often, these potential sites are remote and hence require robust sensors that require minimal maintenance that are not affected strongly by soiling. Therefore, Rotating Shadowband Irradiometers (RSI) are widely used for resource assessment. To achieve the required accuracy, corrections for the raw values of RSIs depending on systematic temperature, incidence angle and spectral errors must be used, and a thorough calibration of the sensor head must be applied. The existing correction functions are derived from comparisons of RSIs to thermopile radiometers at selected sites and therefore empirical. Their accuracy is considered to be site dependent. In this work a new correction and calibration method is presented that removes the systematic errors using a physical approach. It is based on information of the sensor properties as well as measurements of its directional response, and incorporates the atmospheric conditions at the measurement site. In this case, no empiric relations obtained from a specific site are required. The method requires estimates of the current DHI and GHI spectra during each measurement of the RSI. Based on these spectra, a spectral correction, which includes a spectrum dependent temperature correction, can be made without employing empirical relationships. The new physical calibration and correction method is tested at three sites and reaches similar results compared to the empirical functions. This is already achieved with rudimentary estimations of the GHI and DHI spectra and we expect that these estimations can be improved in the future. The results indicate that the physical approach reduces the problematic location dependence of the current calibration and correction methods. The physical correction and calibration method show promise for a further improvement of the RSI accuracy.

47 OTHER INSTRUMENTATION↗
NASA NTRS2005

Looking for systematic error in scale from terrestrial reference frames derived from DORIS data

The long-term stability of the scale of Terrestrial Reference Frames is directly linked with station height determination and is critical for several scientific studies, such as global mean sea level rise or ocean circulation with consequences on global warming studies. In recent International Terrestrial Reference Frame solutions, the DORIS technique was not sonsidered able to provide any useful information on scale. We have analyzed three different DORIS time series of coordinates performed independently using different software packages.

Terrestrial Reference Frame (TRF)↗
DOE OSTI2024

Halogen Thermochemistry Assessed with Density Functional Theory: Systematic Errors, Swift Corrections and Effects on Electrochemistry

Abstract Despite its sizable errors, density functional theory (DFT) is extensively used to evaluate thermochemical properties of gases, liquids and their interfaces with solids. As numerous halogen‐containing compounds appear as reactants, products and/or electrolytes in electrochemical reactions, and ionic effects are currently an active area of research, it is important to evaluate the accuracy of DFT for halogen thermochemistry. Herein, we assess the formation energies of interhalogens, hydrogen halides, diatomic and atomic halogens and their ions using six widespread functionals at the GGA, meta‐GGA and hybrid levels. We observe that DFT errors with respect to experiments are correlated with the electronegativity of the species and there are systematic trends across functionals, such that swift corrections were devised. Specifically, the average of the mean absolute errors for the six functionals decreased from 0.19 eV before the corrections to 0.08 eV after them. Besides, the overall maximum absolute error (MAX) decreased from 0.76 to 0.44 eV and the average of the MAXs decreased from 0.51 to 0.24 eV. Finally, we illustrate the qualitative and quantitative impact of gas‐phase errors on the predictions of surface Pourbaix diagrams.

Chemistry↗
NASA NTRS1986

Systematic errors in determining the propagation direction of interplanetary Alfvenic fluctuations

Analyses of Alfvenic fluctuations in the solar wind contain a systematic effect in which outward propagation is favored. The effect is generally small at and beyond 1 AU in a Mach 10 flow but can become important where the Mach number is lower, e.g., inside 1 AU. If the propagation speeds of the inward and outward propagating Alfvenic fluctuations are properly included, this systematic effect can be removed. A technique for doing this is illustrated using both artificial and spacecraft data. The results suggest that time intervals originally thought to be outward propagating sometimes contain wave number bands in the cross helicity spectrum of inward propagating Alfvenic fluctuations.

Goldstein, M. L.↗
DOE OSTI2018

Constituent quarks and systematic errors in mid-rapidity charged multiplicity dN ch /dη distributions

Centrality definition in A + A collisions at colliders such as RHIC and LHC suffers from a correlated systematic uncertainty caused by the efficiency of detecting a p + p collision (50 ± 5% for PHENIX at RHIC). In A + A collisions where centrality is measured by the number of nucleon collisions, N coll , or the number of nucleon participants, N part , or the number of constituent quark participants, N qp , the error in the efficiency of the primary interaction trigger (Beam–Beam Counters) for a p + p collision leads to a correlated systematic uncertainty in N part , N coll or N qp which reduces binomially as the A + A collisions become more central. If this is not correctly accounted for in projections of A + A to p + p collisions, then mistaken conclusions can result. Finally, a recent example is presented in whether the mid-rapidity charged multiplicity per constituent quark participant d(N ch /dη)/N qp in Au + Au at RHIC was the same as the value in p + p collisions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1977

Procedures for dealing with certain types of noise and systematic errors common to many Hadamard transform optical systems

Sources of noise and error correcting procedures characteristic of Hadamard transform optical systems were investigated. Reduction of spectral noise due to noise spikes in the data, the effect of random errors, the relative performance of Fourier and Hadamard transform spectrometers operated under identical detector-noise-limited conditions, and systematic means for dealing with mask defects are among the topics discussed. The distortion in Hadamard transform optical instruments caused by moving Masks, incorrect mask alignment, missing measurements, and diffraction is analyzed and techniques for reducing or eliminating this distortion are described.

Harwit, M.↗
DOE OSTI2023

BICEP/Keck. XVII. Line-of-sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors

We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum ${A}_{L}^{\phi \phi }=0.95\pm 0.20$. We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic term g aγ ≤ 2.6 × 10 -2 /H I , where H I is the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 Mpc B 1Mpc ≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple "crinkly surface" model of patchy reionization, finding A τ < 0.19 (2σ) for the coherence scale of L c = 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, the EB and TB quadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spurious B-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Quest for the Inflationary Spectral Runnings in the Presence of Systematic Errors

Cosmological inflation suggests that the scalar spectral index "runs" with scale. Constraints on the values of the spectral runnings, ${\alpha }_{s}\equiv {{dn}}_{s}/d\,\mathrm{ln}\,k$ and ${\beta }_{s}\equiv d{\alpha }_{s}/d\,\mathrm{ln}\,k$, therefore provide a fundamental test of the physics of inflation. In this work, we review the feasibility of measuring the runnings when information from upcoming large-volume galaxy surveys is used to supplement the information provided by a cosmic microwave background (CMB)-S4 experiment, particularly focusing on the effect of including high-k, nonlinear scales. Since these measurements will be sensitive to modeling uncertainties for the nonlinear power spectrum, we examine how three different ways of parameterizing those systematics—introducing zero, two, or several hundred nuisance parameters—affect constraints and protect against parameter biases. Considering statistical errors alone, we find that including strongly nonlinear scales can substantially tighten constraints. However, these constraints weaken to levels not much better than those from a CMB-S4 experiment alone when we limit our analysis to scales where estimates are not strongly affected by systematic biases. Given these considerations, near-future large-scale structure (LSS) surveys are unlikely to add much information to the CMB-S4 measurement of the first running α s . There is more potential for improvement for the second running, β s , for which LSS information will allow constraints to be improved by a factor of 3–4 relative to using the CMB alone. Though these limitations are still above the value predicted by slow-roll inflation, they do probe regions of parameter space relevant to nonstandard inflationary models with large runnings, for example, those that can generate an appreciable abundance of primordial black holes.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1992

COBE Differential Microwave Radiometers - Preliminary systematic error analysis

The techniques available for the identification and subtraction of sources of dynamic uncertainty from data of the Differential Microwave Radiometer (DMR) instrument aboard COBE are discussed. Preliminary limits on the magnitude in the DMR 1 yr maps are presented. Residual uncertainties in the best DMR sky maps, after correcting the raw data for systematic effects, are less than 6 micro-K for the pixel rms variation, less than 3 micro-K for the rms quadruple amplitude of a spherical harmonic expansion, and less than 30 micro-(K-squared) for the correlation function.

Kogut, A.↗
NASA NTRS2016

Systematic Error Mitigation for the PIXIE Instrument

The Primordial Ination Explorer (PIXIE) uses a nulling Fourier Transform Spectrometer to measure the absoluteintensity and linear polarization of the cosmic microwave background and diuse astrophysical foregrounds.PIXIE will search for the signature of primordial ination and will characterize distortions from a blackbodyspectrum, both to precision of a few parts per billion. Rigorous control of potential instrumental eects isrequired to take advantage of the raw sensitivity. PIXIE employs a highly symmetric design using multipledierential nulling to reduce the instrumental signature to negligible levels. We discuss the systematic errorbudget and mitigation strategies for the PIXIE mission.

Kogut, Alan↗
DOE OSTI2021

Regularized machine learning on molecular graph model explains systematic error in DFT enthalpies

Abstract A major goal of materials research is the discovery of novel and efficient heterogeneous catalysts for various chemical processes. In such studies, the candidate catalyst material is modeled using tens to thousands of chemical species and elementary reactions. Density Functional Theory (DFT) is widely used to calculate the thermochemistry of these species which might be surface species or gas-phase molecules. The use of an approximate exchange correlation functional in the DFT framework introduces an important source of error in such models. This is especially true in the calculation of gas phase molecules whose thermochemistry is calculated using the same planewave basis set as the rest of the surface mechanism. Unfortunately, the nature and magnitude of these errors is unknown for most practical molecules. Here, we investigate the error in the enthalpy of formation for 1676 gaseous species using two different DFT levels of theory and the ‘ground truth values’ obtained from the NIST database. We featurize molecules using graph theory. We use a regularized algorithm to discover a sparse model of the error and identify important molecular fragments that drive this error. The model is robust to rigorous statistical tests and is used to correct DFT thermochemistry, achieving more than an order of magnitude improvement.

36 MATERIALS SCIENCE↗