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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

Improved Verification for Aerospace Systems

Aerospace systems are subject to many stringent performance requirements to be verified with low risk. This report investigates verification planning using conditional approaches vice the standard classical statistical methods, and usage of historical surrogate data for requirement validation and in verification planning. The example used in this report to illustrate the results of these investigations is a proposed mission assurance requirement with the concomitant maximum acceptable verification risk for the NASA Constellation Program Orion Launch Abort System (LAS). This report demonstrates the following improvements: 1) verification planning using conditional approaches vice classical statistical methods results in plans that are more achievable and feasible; 2) historical surrogate data can be used to bound validation of performance requirements; and, 3) incorporation of historical surrogate data in verification planning using conditional approaches produces even less costly and more reasonable verification plans. The procedures presented in this report may produce similar improvements and cost savings in verification for any stringent performance requirement for an aerospace system.

Powell, Mark A.↗

A Rapid Population Assessment Method for Wild Pigs Using Baited Cameras at 3 Study Sites

ABSTRACT Reliable and efficient population estimates are a critical need for effective management of invasive wild pigs ( Sus scrofa ). We evaluated the use of 10‐day camera grids for rapid population assessment (RPA) of wild pigs at 3 study sites that varied in vegetation communities and wild pig densities. Study areas included Buck Island Ranch, Florida; Tejon Ranch, California; and the Savannah River Site, South Carolina, USA, during 2016–2018. Rapid population assessments grids were composed of baited camera traps spaced approximately 500 or 750 m apart. Two RPA grids were deployed per study site and each grid was deployed twice (4–6 months apart) to assess changes in response to season or population control efforts. We assessed the ability of RPA grids to track population trends, how camera number influenced estimate precision, and how relative abundance indices related to density estimates. We detected changes in occupancy probability, detection probability, and N‐mixture estimates following removal operations and between seasons, but the ability of RPA grids to track population trends was dependent on the statistical method used and number of cameras traps. Increasing the number of cameras traps used in RPA grids increased precision, and these results can be used in determining survey design and estimate choice. We found that estimates of occupancy probability, detection probability, and N‐mixture estimates were positively correlated with spatially explicit capture–recapture density estimates. Thus, these less labor‐intensive estimates from RPA grids showed potential to index the relative abundance of wild pigs in some systems. Our evaluation of RPAs indicates that using study‐specific combinations of statistical method and number of cameras can provide a useful tool for monitoring wild pig presence, tracking population trends, and evaluating the effectiveness of management actions. © 2020 The Wildlife Society.

Schlichting, Peter E.↗

An analytic treatment of gravitational microlensing for sources of finite size at large optical depths

Statistical methods are developed for gravitational lensing in order to obtain analytic expressions for the average surface brightness that include the effects of microlensing by stellar (or other compact) masses within the lensing galaxy. The primary advance here is in utilizing a Markoff technique to obtain expressions that are valid for sources of finite size when the surface density of mass in the lensing galaxy is large. The finite size of the source is probably the key consideration for the occurrence of microlensing by individual stars. For the intensity from a particular location, the parameter which governs the importance of microlensing is determined. Statistical methods are also formulated to assess the time variation of the surface brightness due to the random motion of the masses that cause the microlensing.

Deguchi, Shuji↗

Tropical Tropospheric Ozone Trends (1990 to 2022): A Re-evaluation Based on SHADOZ and IAGOS Profiles and TOMS/OMI Columns

Changes in tropical tropospheric ozone (TTO) are of importance because this region spans roughly a third of the Earth and portions of it are experiencing variability in trends of ozone precursors (CO, NO x , CH 4 and nonmethane hydrocarbons) associated with economic growth and fires. In addition to ozone changes affecting radiative forcing, tropical ozone is an important source of the OH radical and thus, the oxidizing capacity of the planet (Thompson, 1992). Recent studies examining TTO trends satellite and in-situ observations over the past ~25 years include: Thompson et al., JGR, 2021; Gaudel et al., ACP, 2023; Stauffer et al., ACP, 2023. The results show considerable regional and seasonal variability in TTO trends and sensitivity to data selection, frequency, and statistical method used. The satellite data vary most widely in method, time period and reliability. Here we revisit trends for the 1990-2022 period with the best-characterized buv-based satellite products that span that period (derived from TOMS and OMI, Ziemke et al., 2019). The satellite-based trends are compared to trends based on in-situ data from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network (1998-2022), measurements from selected pre-SHADOZ and IAGOS commercial aircraft data (Gaudel et al., 2023). Among sensitivities examined are the dependence of ozone trends on start and end years, impacts of ENSO events and the COVID-19 perturbation to emissions. Two statistical methods are used, quantile regression (QR) and multiple linear regression (MLR). Trends of total TTO, ozone segments in the boundary layer (to ~700 hPa), and free troposphere (700-300 hPa) are compared.

ozone, OMI, tropospheric ozone, SHADOZ↗

Cosmic evolution of long gamma-ray burst luminosity

The cosmic evolution of gamma-ray burst (GRB) luminosity is essential for revealing the GRB physics and for using GRBs as cosmological probes. We investigate the luminosity evolution of long GRBs with a large sample of 258 Swift/BAT GRBs. By describing the peak luminosity evolution of individual GRBs as L{sub p}∝(1+z){sup k}, we get k=1.49±0.19 using the nonparametric τ statistics method without considering observational biases of GRB trigger and redshift measurement. By modeling these biases with the observed peak flux and characterizing the peak luminosity function of long GRBs as a smoothly broken power law with a break that evolves as L{sub b}∝(1+z){sup k{sub b}}, we obtain k{sub b}=1.14{sub −0.47}{sup +0.99} through simulations based on the assumption that the long GRB rate follows the star formation rate incorporating the cosmic metallicity history. The derived k and k{sub b} values are systematically smaller than those reported in previous papers. By removing the observational biases of the GRB trigger and redshift measurement based on our simulation analysis, we generate mock complete samples of 258 and 1000 GRBs to examine how these biases affect the τ statistics method. We get k=0.94±0.14 and k=0.80±0.09 for the two samples, indicating that these observational biases may lead to overestimating the k value. With the large uncertainty of k{sub b} derived from our simulation analysis, one cannot even convincingly argue for a robust evolution feature of the GRB luminosity.

79 ASTRONOMY AND ASTROPHYSICS↗

Finding the magnetopause location using soft X-ray observations and a statistical inverse method

Variability in the location and shape of the dayside magnetopause is attributed to magnetic reconnection, a fundamental process that enables the transfer of mass, energy, and momentum from the solar wind into the magnetosphere. The spatial and temporal properties of the magnetopause, under varying solar and magnetospheric conditions, remain largely unknown because empirical studies using in-situ observations are challenging to interpret. Global wide field-of-view (FOV) imaging is the only means to simultaneously observe the spatial distribution of the plasma properties over the vast dayside magnetospheric region and, subsequently, quantify the energy transport from the interplanetary medium into the terrestrial magnetosphere. Two upcoming missions, ESA/CAS SMILE and NASA’s LEXI will provide wide-field imagery of the dayside magnetosheath in soft X-rays, an emission generated by charge exchange interactions between high charge-state heavy ions of solar wind origin and exospheric neutral atoms. High-cadence two-dimensional observations of the magnetosheath will allow the estimation of dynamic properties of its inner boundary, the magnetopause, and enable studies of its response to changes in the solar wind dynamic pressure and interplanetary magnetic field orientation. This work introduces a statistically-based estimation approach based on inverse theory to estimate the spatial distribution of magnetosheath soft X-ray emissivities and, with this, identify the location of the magnetopause over the Sun−Earth line. To do so, we simulate the magnetosheath structure using the MHD-based OpenGGCM model and generate synthetic soft X-ray images using LEXI’s orbit and attitude information. Our results show that 3-D estimations using the described statistically-based technique are robust against Poisson-distributed shot noise inherent to soft X-ray images. Also, our proposed methodology shows that the accuracy of both three-dimensional (3-D) estimation and the magnetopause standoff distance calculation highly depends on the observational point.

Gonzalo Cucho-Padin↗

Comparing Global Spray Combustion Characteristics and Local Shot-to-Shot Variations in a Reacting n -Heptane Spray

In support of efforts to develop improved models of turbulent spray behavior and combustion in diesel engines, experimental data and analysis must be obtained for guidance and validation. For Reynolds-averaged Navier–Stokes (RANS)-based Computational fluid dynamics (CFD) modeling approaches, representative ensemble average experimental results are important. For high-fidelity models such as large eddy simulations (LES)-based CFD, precise individual experimental results are desirable. However, making comparisons between a given experiment and LES is a challenge since local parameters cannot be directly compared. In this work, an optically accessible constant pressure flow rig (CPFR) is utilized to acquire diesel-like fuel injection and reaction behavior simultaneously with three optical diagnostic techniques: rainbow Schlieren deflectometry (RSD), OH* chemiluminescence (OH*), and two-color pyrometry (2CP). The CPFR allows a large number of repeated injection experiments to be performed for statistical analysis and convergence using ensemble-averaging techniques, while maintaining highly repeatable test conditions. Even for stable test conditions, variations in local turbulent fuel–air mixing introduce variability, which manifests as significant differences in OH* and 2CP results. Experimental measurements of characteristic parameters including liquid and vapor jet penetration, liftoff length, soot temperature and concentration, and turbulent flame speed, along with the shot-to-shot variability of each dataset, are presented and discussed. Finally, a statistical method is utilized to analyze the extent of this variability, and to identify superlative injections within the dataset for discussion and analysis of shot-to-shot variations.

42 ENGINEERING↗

Resolving phase stability in the Ti-O binary with first-principles statistical mechanics methods

The Ti-O system consists of a multitude of stable and metastable oxides that are used in wide ranging applications. In this work we investigate phase stability in the Ti-O binary from first principles. We perform a systematic search for ground state structures as a function of oxygen concentration by considering oxygen-vacancy and/or titanium-vacancy orderings over four parent crystal structures: (i) hcp Ti, (ii) ω-Ti, (iii) rocksalt, and (iv) hcp oxygen containing interstitial titanium. We explore phase stability at finite temperature using cluster expansion Hamiltonians and Monte Carlo simulations. The calculations predict a high oxygen solubility in hcp Ti and the stability of suboxide phases that undergo order-disorder transitions upon heating. Vacancy ordered rocksalt phases are also predicted at low temperature that disorder to form an extended solid solution at high temperatures. Predicted stable and metastable phase diagrams are qualitatively consistent with experimental observations, however, important discrepancies are revealed between first-principles density functional theory predictions of phase stability and the current understanding of phase stability in this system.

36 MATERIALS SCIENCE↗

Method of statistical filtering

Minimal formula for bounding the cross correlation between a random forcing function and the state error when this correlation is unknown is used in optimal linear filter theory applications. Use of the bound results in overestimation of the estimation-error covariance.

Battin, R. H.↗

Lifetimes and Reliabilities of Bevel-Gear Drive Trains

Statistical methods used to predict system lifetimes from component lifetimes. Report shows how to use information to determine system life of drive train, using methods of probability and statistics. Presents life and reliability model for bevel-gear drive trains. Bevel-gear and support-bearing lives analyzed for each gear and bearing in drive train, with results statistically combined to produce system life for entire drive train. Numerical example included.

Lewicki, D.↗

Reliability Models and Attributable Risk

The intention of this report is to bring a developing and extremely useful statistical methodology to greater attention within the Safety, Reliability, and Quality Assurance Office of the NASA Johnson Space Center. The statistical methods in this exposition are found under the heading of attributable risk. Recently the Safety, Reliability, and Quality Assurance Office at the Johnson Space Center has supported efforts to introduce methods of medical research statistics dealing with the survivability of people to bear on the problems of aerospace that deal with the reliability of component hardware used in the NASA space program. This report, which describes several study designs for which attributable risk is used, is in concert with the latter goals. The report identifies areas of active research in attributable risk while briefly describing much of what has been developed in the theory of attributable risk. The report, which largely is a report on a report, attempts to recast the medical setting and language commonly found in descriptions of attributable risk into the setting and language of the space program and its component hardware.

Jarvinen, Richard D.↗

Systematic analysis of coding and noncoding DNA sequences using methods of statistical linguistics

We compare the statistical properties of coding and noncoding regions in eukaryotic and viral DNA sequences by adapting two tests developed for the analysis of natural languages and symbolic sequences. The data set comprises all 30 sequences of length above 50 000 base pairs in GenBank Release No. 81.0, as well as the recently published sequences of C. elegans chromosome III (2.2 Mbp) and yeast chromosome XI (661 Kbp). We find that for the three chromosomes we studied the statistical properties of noncoding regions appear to be closer to those observed in natural languages than those of coding regions. In particular, (i) a n-tuple Zipf analysis of noncoding regions reveals a regime close to power-law behavior while the coding regions show logarithmic behavior over a wide interval, while (ii) an n-gram entropy measurement shows that the noncoding regions have a lower n-gram entropy (and hence a larger "n-gram redundancy") than the coding regions. In contrast to the three chromosomes, we find that for vertebrates such as primates and rodents and for viral DNA, the difference between the statistical properties of coding and noncoding regions is not pronounced and therefore the results of the analyses of the investigated sequences are less conclusive. After noting the intrinsic limitations of the n-gram redundancy analysis, we also briefly discuss the failure of the zeroth- and first-order Markovian models or simple nucleotide repeats to account fully for these "linguistic" features of DNA. Finally, we emphasize that our results by no means prove the existence of a "language" in noncoding DNA.

NASA Discipline Number 14-10↗

Why Use Geo-statistics For Nuclear Decommissioning Projects? - 15567

Before nuclear facilities are dismantled, and contaminated sites remediated, their initial radiological state must be characterized. Combining historical information, non-destructive measurements and lab analysis results, the statistical method of geo-statistics allows all available data for 2D or 3D contamination mapping to be integrated and enhanced, and helps quantify estimation uncertainties. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Multi-Axis Accelerometer Calibration System

A low-cost, portable, and simplified system has been developed that is suitable for in-situ calibration and/or evaluation of multi-axis inertial measurement instruments. This system overcomes facility restrictions and maintains or improves the calibration quality for users of accelerometer-based instruments with applications in avionics, experimental wind tunnel research, and force balance calibration applications. The apparatus quickly and easily positions a multi-axis accelerometer system into a precisely known orientation suitable for in-situ quality checks and calibration. In addition, the system incorporates powerful and sophisticated statistical methods, known as response surface methodology and statistical quality control. These methods improve calibration quality, reduce calibration time, and allow for increased calibration frequency, which enables the monitoring of instrument stability over time.

Finley, Tom↗

Quantifying uncertainty in analysis of shockless dynamic compression experiments on platinum. II. Bayesian model calibration

Dynamic shockless compression experiments provide the ability to explore material behavior at extreme pressures but relatively low temperatures. Typically, the data from these types of experiments are interpreted through an analytic method called Lagrangian analysis. Here, in this work, alternative analysis methods are explored using modern statistical methods. Specifically, Bayesian model calibration is applied to a new set of platinum data shocklessly compressed to 570 GPa. Several platinum equation-of-state models are evaluated, including traditional parametric forms as well as a novel non-parametric model concept. The results are compared to those in Paper I obtained by inverse Lagrangian analysis. The comparisons suggest that Bayesian calibration is not only a viable framework for precise quantification of the compression path, but also reveals insights pertaining to trade-offs surrounding model form selection, sensitivities of the relevant experimental uncertainties, and assumptions and limitations within Lagrangian analysis. The non-parametric model method, in particular, is found to give precise unbiased results and is expected to be useful over a wide range of applications. The calibration results in estimates of the platinum principal isentrope over the full range of experimental pressures to a standard error of 1.6%, which extends the results from Paper I while maintaining the high precision required for the platinum pressure standard.

Brown, Justin Lee↗

Statistical Influence

Advancing the spread and practice of statistics enhances an organization’s ability to successfully achieve their mission. While there may be leadership mandates to employ statistical methods, often the spread of statistical concepts flourishes more effectively through the practice of statistical influence. At first glance, the term influence may seem to imply a passive and unenthusiastic posture toward promoting organizational change. However, a classical definition states that ,“In a general sense, influence denotes power whose operation is invisible and known only by its effects, or a power whose cause and operation are unseen.” This definition articulates the powerful and yet subtle aspects of influence that embodies the theme of this presentation. Stated plainly, powerful statistical concepts become more widely known and engrained primarily through demonstrated impact; a strategy known only by its effects. In this presentation, elements of statistical influence are exemplified through practice at NASA.

Peter A. Parker↗

The National Climate Data Base (NCDB): A Bias-Corrected High-Resolution Climate Dataset

Assessing renewable energy resources under future climate scenarios has been highlighted in recent years to analyze and understand potential impacts of future change in renewable generation on the power sector. Solar energy is well-known as the most plentiful among various renewable resources and usually converted to electricity using photovoltaics (PV) technologies, and the global deployment of PV technology has increased rapidly in recent decades. In this study, we develop a statistical technique to downscale the future projection of solar irradiance for PV energy-related applications. A set of Regional Climate Model (RCM)-based projections obtained from the North American Coordinated Regional Climate Downscaling Experiment (NA-CORDEX) are used as inputs to statistical methods to generate high-resolution global horizontal irradiance (GHI) over the contiguous United States (CONUS). The main steps of the statistical downscaling method include (1) regridding RCM output (0.22 degree and daily resolutions) to handle the modeled-observed data sets on a common grid, (2) correcting bias of RCM GHI using satellite-derived observation, and (3) implementing temporal and spatial downscaling to generate GHI at 8-km and hourly resolution. Basically, complex physical processes and interactions between solar radiation and various atmospheric constituents lead solar irradiance to be highly variable and uncertain. Underrepresentation of clouds from the RCM parameterizations is the main source of error and uncertainty in modeling solar irradiance. Thus, we adapt and use the high-quality satellite-derived data from the National Solar Radiation Database (NSRDB) to analyze the bias and error of RCM GHI as well as estimate the statistical parameters for spatial and temporal downscaling. This presentation will summarize the comprehensive analysis conducted to produce and assess the results under two climate scenarios (RCP4.5 and RCP8.5). We will also present a detailed validation demonstrating the strengths of the proposed downscaling method and future extension of this research.

climate data↗