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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2009

Model Checking - My 27-Year Quest to Overcome the State Explosion Problem

Model Checking is an automatic verification technique for state-transition systems that are finite=state or that have finite-state abstractions. In the early 1980 s in a series of joint papers with my graduate students E.A. Emerson and A.P. Sistla, we proposed that Model Checking could be used for verifying concurrent systems and gave algorithms for this purpose. At roughly the same time, Joseph Sifakis and his student J.P. Queille at the University of Grenoble independently developed a similar technique. Model Checking has been used successfully to reason about computer hardware and communication protocols and is beginning to be used for verifying computer software. Specifications are written in temporal logic, which is particularly valuable for expressing concurrency properties. An intelligent, exhaustive search is used to determine if the specification is true or not. If the specification is not true, the Model Checker will produce a counterexample execution trace that shows why the specification does not hold. This feature is extremely useful for finding obscure errors in complex systems. The main disadvantage of Model Checking is the state-explosion problem, which can occur if the system under verification has many processes or complex data structures. Although the state-explosion problem is inevitable in worst case, over the past 27 years considerable progress has been made on the problem for certain classes of state-transition systems that occur often in practice. In this talk, I will describe what Model Checking is, how it works, and the main techniques that have been developed for combating the state explosion problem.

Clarke, Ed↗
NASA NTRS2012

Best Practices for the Application of Functional Near Infrared Spectroscopy to Operator State Sensing

Functional Near Infrared Spectroscopy (fNIRS) is an emerging neuronal measurement technique with many advantages for application in operational and training contexts. Instrumentation and protocol improvements, however, are required to obtain useful signals and produce expeditiously self-applicable, comfortable and unobtrusive headgear. Approaches for improving the validity and reliability of fNIRS data for the purpose of sensing the mental state of commercial aircraft operators are identified, and an exemplary system design for attentional state monitoring is outlined. Intelligent flight decks of the future can be responsive to state changes to optimally support human performance. Thus, the identification of cognitive performance decrement, such as lapses in operator attention, may be used to predict and avoid error-prone states. We propose that attentional performance may be monitored with fNIRS through the quantification of hemodynamic activations in cortical regions which are part of functionally-connected attention and resting state networks. Activations in these regions have been shown to correlate with behavioral performance and task engagement. These regions lie beneath superficial tissue in head regions beyond the forehead. Headgear development is key to reliably and robustly accessing locations beyond the hair line to measure functionally-connected networks across the whole head. Human subject trials using both fNIRS and functional Magnetic Resonance Imaging (fMRI) will be used to test this system. Data processing employs Support Vector Machines for state classification based on the fNIRS signals. If accurate state classification is achieved based on sensed activation patterns, fNIRS will be shown to be useful for monitoring attentional performance.

Harrivel, Angela R.↗
NASA NTRS2013

A Turn-Projected State-Based Conflict Resolution Algorithm

State-based conflict detection and resolution (CD&R) algorithms detect conflicts and resolve them on the basis on current state information without the use of additional intent information from aircraft flight plans. Therefore, the prediction of the trajectory of aircraft is based solely upon the position and velocity vectors of the traffic aircraft. Most CD&R algorithms project the traffic state using only the current state vectors. However, the past state vectors can be used to make a better prediction of the future trajectory of the traffic aircraft. This paper explores the idea of using past state vectors to detect traffic turns and resolve conflicts caused by these turns using a non-linear projection of the traffic state. A new algorithm based on this idea is presented and validated using a fast-time simulator developed for this study.

Butler, Ricky W.↗
NASA NTRS2012

An Ontology for State Analysis: Formalizing the Mapping to SysML

State Analysis is a methodology developed over the last decade for architecting, designing and documenting complex control systems. Although it was originally conceived for designing robotic spacecraft, recent applications include the design of control systems for large ground-based telescopes. The European Southern Observatory (ESO) began a project to design the European Extremely Large Telescope (E-ELT), which will require coordinated control of over a thousand articulated mirror segments. The designers are using State Analysis as a methodology and the Systems Modeling Language (SysML) as a modeling and documentation language in this task. To effectively apply the State Analysis methodology in this context it became necessary to provide ontological definitions of the concepts and relations in State Analysis and greater flexibility through a mapping of State Analysis into a practical extension of SysML. The ontology provides the formal basis for verifying compliance with State Analysis semantics including architectural constraints. The SysML extension provides the practical basis for applying the State Analysis methodology with SysML tools. This paper will discuss the method used to develop these formalisms (the ontology), the formalisms themselves, the mapping to SysML and approach to using these formalisms to specify a control system and enforce architectural constraints in a SysML model.

Wagner, David A.↗
NASA NTRS2011

Excited State Chemistry in the Free Stream of the NASA IHF Arc Jet Facility Observed by Emission Spectroscopy

Spectroscopic measurements of non-equilibrium emission were made in the free stream of the 60 megawatts Interaction Heating Facility at NASA Ames Research Center. In the visible near infrared wavelength region, the most prominent emission was from molecular N2, and in the ultra violet region, the spectra were dominated by emission from molecular NO. The only atomic lines observed were those of copper (an erosion product of the electrodes). The bands of the 1st Positive system of N2 (if B is true then A is true) differed significantly from spectra computed spectra assuming only thermal excitation, suggesting overpopulation of the high vibrational states of the B state of N2. Populations of these high vibrational levels (peaking at v (sub upper) equals 13) of the N2 B state were determined by scaling simulated spectra; calculations were performed for each upper vibrational state separately. The experimental-theoretical procedure was repeated for several radial positions away from the nozzle axis to obtain spatial distributions of the upper state populations; rotational symmetry of the flow was assumed in simulations. The overpopulation of the high vibrational levels has been interpreted as the effect of inverse pre-dissociation of neutral atoms in the N2 A state, which populates the N2 B state through a level crossing process at v (sub upper) is greater than 10.

arc-jet testing↗
NASA NTRS2020

Exploring Cognitive States: Methods for Detecting Physiological Temporal Fingerprints

Cognitive state detection and its relationship to observable physiologically telemetry has been utilized for many human-machine and human-cybernetic applications. This paper aims at understanding and addressing if there are unique psychophysiological patterns over time, a ”physiological temporal fingerprint”, that is associated with specific cognitive states. This preliminary work involves commercial airline pilots completing experimental benchmark task inductions of three cognitive states: 1) Channelized Attention (CA); 2) High Workload (HW); and 3) Low Workload (LW). We approach this objective by modeling these "fingerprints" through the use of Hidden Markov Models and Entropy analysis to evaluate if the transitions over time are complex or rhythmic/predictable by nature. Our results indicate that cognitive states do have unique complexity of physiological sequences that are statistically different from other cognitive states. More specifically, CA has a significantly higher temporal psychophysiological complexity than HW and LW in EEG and ECG telemetry signals. With regards to respiration telemetry, CA has a lower temporal psychophysiological complexity than HW and LW. Through our preliminary work, addressing this unique underpinning can inform whether these underlying dynamics can be utilized to understand how humans transition between cognitive states and for improved detection of cognitive states.

Napoli, Nicholas J.↗
NASA NTRS2021

Rapid accretion state transitions following the tidal disruption event AT2018fyk

Following a tidal disruption event (TDE), the accretion rate can evolve from quiescent to near- Eddington levels and back over months{years timescales. This provides a unique opportunity to study the formation and evolution of the accretion flow around supermassive black holes (SMBHs). We present two years of multi-wavelength monitoring observations of the TDE AT2018fyk at X-ray, UV, optical and radio wavelengths. We identify three distinct accretion states and two state transitions between them. These appear remarkably similar to the behaviour of stellar-mass black holes in outburst. The X-ray spectral properties show a transition from a soft (thermal-dominated) to a hard (power-law dominated) spectral state around Lbol ~few x 10^(-2) LEdd, and the strengthening of the corona over time ~100-200 days after the UV/optical peak. Contemporaneously, the spectral energy distribution (in particular, the UV-to-X-ray spectral slope alphaox ) shows a pronounced softening as the outburst progresses. The X-ray timing properties also show a marked change, initially dominated by variability at long (>day) timescales while a high frequency (~10-3 Hz) component emerges after the transition into the hard state. At late times (~500 days after peak), a second accretion state transition occurs, from the hard into the quiescent state, as identi fied by the sudden collapse of the bolometric (X-ray+UV) emission to levels below 10-3.4 LEdd. Our fi ndings illustrate that TDEs can be used to study the scale (in)variance of accretion processes in individual SMBHs. Consequently, they provide a new avenue to study accretion states over seven orders of magnitude in black hole mass, removing limitations inherent to commonly used ensemble studies.

T. Wevers↗
NASA NTRS2020

On Perspectives of Generating Quasi-Fock State via Resonant Self-Phase-Modulation

Optical resonators with cubic nonlinearity were among the ?rst simplest physical systems proposed for generation of squeezed states of light as well as for veri?cation of quantum nondemolition measurement concept. These conventional squeezed states are characterized with Gaussian statistics and positive Wigner function and are frequently treated as semiclassical. In contrast, it is known that the quantum states resulting from the higher order self-phase modulation are characterized with negative Wigner function. Such states can be transformed to an imperfect Fock state via classical biasing. Using these known features, we have developed an experiment strategy for observation and characterization of the nonclassical state in a system based on a high-Q nonlinear optical microcavity. We discuss technical limitations for the state observation associated with the losses in the system and technical noise of the classical optical sources involved in the measurement.

Bilenko, I. A.↗
NASA NTRS2023

Measurement Report :Emission Factors of NH3 and NHx for Wildfires and Agricultural Fires in the United States

During the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study, the NASA DC-8 carried out in situ chemical measurements in smoke plumes emitted from wildfires and agricultural fires in the contiguous United States. The DC-8 payload included a modified proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) for the fast measurement of gaseous ammonia (NH 3 ) and a high-resolution time-of-flight aerosol mass spectrometer (AMS) for the fast measurement of submicron particulate ammonium (NH 4 + ). We herein report data collected in smoke plumes emitted from 6 wildfires in the Western United States, 2 prescribed grassland fires in the Central United States, 1 prescribed forest fire in the Southern United States, and 66 small agricultural fires in the Southeastern United States. Smoke plumes contained double to triple digit ppb levels of NH 3 . In the wildfire plumes, a significant fraction of NH 3 had already been converted to NH 4 + at the time of sampling (≥2 h after emission). Substantial amounts of NH 4 + were also detected in freshly emitted smoke from corn and rice field fires. We herein present a comprehensive set of emission factors of NH 3 and NH x , with NH x = NH 3 + NH 4 + . Average NH 3 and NH x emission factors for wildfires in the Western United States were 1.86±0.75 g kg −1 and 2.47±0.80 g kg −1 of fuel burned, respectively. Average NH 3 and NH x emission factors for agricultural fires in the Southeastern United States were 0.89±0.58 and 1.74±0.92 g kg −1 , respectively. Our data show no clear inverse correlation between modified combustion efficiency (MCE) and NH 3 emissions. The observed NH 3 emissions were significantly higher than measured in previous laboratory experiments in the FIREX FireLab 2016 study.

Laura Tomsche↗
NASA NTRSDate not supplied

Asymmetric Flow State Switching in the Space Launch System Block 2 Liftoff Environment

An in-depth investigation was conducted at the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel to evaluate flow state switching in the liftoff flow environment of the Space Launch System Block 2 Crew launch vehicle using force measurements, two-component particle image velocimetry, and tuft flow visualization. Multimodal flow states were observed in the gap flow between the centerbody and solid rocket boosters at a range of incoming flow angles and were characterized for the relative strength of state switches. When flow switches occur, the flow is predominantly bimodal, but trimodal flow states are observed with the launch tower downstream of the vehicle. Tuft visualization indicates three-dimensionality during flow state switching, which initiates at one part of the gap and quickly transitions throughout the length of the booster. Due to the long time scales between switches, statistics such as frequency of flow state switches and converged state probabilities cannot be established without significantly increased acquisition times.

Lee J. Mears↗
NASA NTRSDate not supplied

Asymmetric Flow State Switching on the Space Launch System (SLS) Block 2 Crew Vehicle

An in-depth investigation was conducted at the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel to evaluate flow state switching in the liftoff flow environment of the Space Launch System Block 2 Crew launch vehicle using side force measurements, two-component particle image velocimetry, and tufts flow visualization. Multimodal flow states were observed in the gap flow between the centerbody and solid rocket boosters at a range of incoming flow angles and were characterized for the relative strength of state switches. When flow switches occur, the flow is predominantly bimodal, but trimodal flow states are observed with the launch tower downstream of the vehicle. Tufts visualization indicates three-dimensionality during flow state switching, which initiates at one part of the gap and quickly transitions throughout the length of the booster. Due to the long time scales between switches, statistics such as frequency of flow state switches and converged state probabilities cannot be established without significantly increased acquisition times.

Lee J. Mears↗
DOE OSTI2023

Summary Analysis of Different Offshore Wind Capacity Density Drivers in Proposed U.S. Projects and Impacts on Progress Towards State and Federal Deployment Targets

Understanding the density of offshore wind development - or the "capacity density" - is important for state and federal offshore wind planning efforts and to track progress towards policy goals. NREL has traditionally assumed a capacity density of 3 megawatts per square kilometer (MW/km2) when estimating the U.S. project pipeline (Musial et al. 2022), but capacity densities for existing European offshore wind farms ranged from 2-19 MW/km2 (Borrmann et al. 2018). We track the expected capacity densities of the proposed U.S. projects in the East Coast and make an analysis by state and by developer to identify what are the capacity density norms in the industry and whether the state in which the development efforts are taking place has some impact on capacity density. We also analyze the effects of the area occupied by station keeping systems on capacity density for lease areas dedicated to floating projects and provide a list of main capacity density drivers. This summary analysis sets a baseline to study how different capacity density drivers could impact the progress towards state and federal deployment targets. Given the currently delineated Renewable Energy Areas in the Outer Continental Shelf (OCS) and the basis from the summary analysis, we estimate the expected offshore wind deployment over time federally and by state and compare it to the state and federal deployment targets. The proposed analysis helps identify gaps and needs to meet state and federal targets, which provides sufficient information to propose strategic supply chain and policy planning with the objective of meeting deployment goals.

capacity density↗
DOE OSTI2025

Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Iridium oxides with high oxidation states have been reported to be effective in enhancing the acidic oxygen evolution reaction (OER) performance. Herein, we develop ultrasmall IrO x nanoparticles (NPs) over titanium nitride (TiN), which undergoes surface oxidation under oxidative conditions to form oxygen-modified TiN (oxi-TiN), enabling the formation of highly oxidized Ir δ+ (δ > 4). This IrO x /oxi-TiN catalyst delivers higher Ir mass activity than commercial IrO 2 , while comparable stability is maintained. The superior OER activity of IrO x /oxi-TiN is further demonstrated in a proton exchange membrane water electrolyzer (PEMWE), requiring only 1.88 V to reach 3 A cm −2 , achieving the U.S. Department of Energy 2025 target (1.90 V at 3 A cm −2 ). In situ X-ray absorption spectroscopy (XAS) confirms that the superior OER activity of IrO x /oxi-TiN originates from highly oxidized Ir δ+ under OER conditions. Further, density functional theory (DFT) calculations reveal a general correlation between the oxidation state of Ir and OER overpotential. Specifically, the introduction of interfacial oxygen at the Ir/TiN interface increases the oxidation state of deposited Ir δ+ from δ < 4 to δ > 4, decreasing the OER overpotential. This study highlights the critical role of high oxidation states of Ir δ+ in enhancing OER activity, providing guidance for the development of advanced acidic OER catalysts.

In situ measurements↗
DOE OSTI2025

Enhancing Acidic Oxygen Evolution Activity by Controlling Oxidation State of Iridium

Iridium oxides with high oxidation states have been reported to be effective in enhancing the acidic oxygen evolution reaction (OER) performance. In this work, we develop ultrasmall IrO x nanoparticles (NPs) over titanium nitride (TiN), which undergoes surface oxidation under oxidative conditions to form oxygen‐modified TiN (oxi‐TiN), enabling the formation of highly oxidized Ir δ+ (δ > 4). This IrO x /oxi‐TiN catalyst delivers higher Ir mass activity than commercial IrO 2 , while comparable stability is maintained. The superior OER activity of IrO x /oxi‐TiN is further demonstrated in a proton exchange membrane water electrolyzer (PEMWE), requiring only 1.88 V to reach 3 A cm −2 , achieving the U.S. Department of Energy 2025 target (1.90 V at 3 A cm −2 ). In situ X‐ray absorption spectroscopy (XAS) confirms that the superior OER activity of IrO x /oxi‐TiN originates from highly oxidized Ir δ+ under OER conditions. Density functional theory (DFT) calculations reveal a general correlation between the oxidation state of Ir and OER overpotential. Specifically, the introduction of interfacial oxygen at the Ir/TiN interface increases the oxidation state of deposited Ir δ+ from δ < 4 to δ > 4, decreasing the OER overpotential. This study highlights the critical role of high oxidation states of Ir δ+ in enhancing OER activity, providing guidance for the development of advanced acidic OER catalysts.

58 GEOSCIENCES↗
DOE OSTI2026

Locally purified maximally mixed states at scale: Entanglement pruning and symmetries

Locally Purified Density Operators (LPDOs) are state-of-the-art tensor network ansatze candidates that efficiently represent mixed quantum states at scale. However, given their non-uniqueness, their representational complexity is generally sub-optimal in practical computations. Here, in this work we perform a comprehensive numerical and analytical analysis and resolve this issue in the experimentally relevant limit where noise depolarizes the density operator into a maximally mixed state. To resolve the sub-optimality issue, we analyze two numerical tools, one analytic method, and detail the relations between them. The numerical tools used are fidelity-preserving truncations and isometric gauge transformations leveraging Riemannian optimizations over entropic objective functions. In addition, by invoking the injectivity and symmetry constraints of the maximally mixed LPDO, we also present analytical closed-form expressions for the disentangler and discuss their relation to numerical optimizers. Further, away from the maximally mixed state, our simulations highlight how the truncation threshold smoothly interpolate, as a function of depolarization, between established matrix product results and our new results. Our work shows how, by minimizing the resources required to represent key states of practical interest in experiment, the efficiency of tensor network algorithms can be substantially increased. This paves the path for uncovering tensor network’s fundamental scalability limits and latent potential in representing the wide locus of mixed quantum states that are accessible on near-term quantum devices.

Gangapuram, Amit Jamadagni [Oak Ridge National Lab↗
DOE OSTI2025

Graph-Learning-Assisted State and Event Tracking for Solar-Penetrated Power Grids with Heterogeneous Data Sources

Unlike transmission systems, distribution systems do not typically contain sufficient metering to enable real-time state estimation. The lack of sufficient real-time measurements prohibits accurate and timely monitoring of the state of distribution systems. As a result, control and optimal operation of distribution systems, especially those containing large numbers of renewable generation units are not possible without proper data and information about the current state of the system. The main motivation of this project is to address this shortcoming by developing an approach which provides “predicted” real-time measurements so that they can be used to execute a distribution system state estimator. Thus, the objective of the project is to make the distribution systems fully observable, such that the hosting capacity for solar generation can be accurately estimated, and unnecessary solar curtailments can be avoided. In order to accomplish this goal, the project investigated the use of a grid-model-informed machine learning (ML) tool which integrates heterogeneous data streams obtained from AMI meters, SCADA as well as PMU measurements and created synchronous measurement snapshots for the state estimator (SE); and developed a hybrid robust SE which provides not only accurate state estimates but also real-time feedback for the ML model refinement.

14 SOLAR ENERGY↗
DOE OSTI2025

Aerosol Particle Mixing State and Composition at AMF3 (Interim Field Campaign Report)

The campaign is designed to support deployment of aerosol sampling equipment at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility’s third ARM Mobile Facility (AMF3) to enable both singe-particle and bulk characterization of the aerosol particles at the field site in Bankhead National Forest, northern Alabama. We are proposing to do this work as part of our proposal “Generalizing aerosol mixing state: synthesis from observations and connection to models,” which has the pre-proposal tracking number PRE-0000035878. The full proposal has Dr. Rachel O’Brien as the Principal Investigator (PI) and Dr. Andy Ault and Dr. Nicole Riemer as Co-PIs. We sought to deploy instruments in winter 2025 and summer 2025 to obtain samples in different seasons, but were delayed by AMF3 set-up and availability of students and PIs. We just completed our first deployment this summer (2025) and we are interested in obtaining samples during this upcoming fall and winter to see the seasonal trends in aerosol mixing state at the site. This will provide a comparison of the impact of biogenic emissions on the mixing state and the chemical composition of the aerosol particles. Overall, the proposed study will provide key information regarding the mixing state of aerosol particles at AMF3 with direct ties to impacts of the particles on cloud formation and light scattering/absorption. From our deployment that ended las week we have some visible observations from our samples. We are observing a regular amount of black carbon on stage 6 of our Micro-Orifice Uniform Deposit Impactor (MOUDI) and we have also observed some short, large increases in aerosol loading. We hope to continue observations of these two features to determine the sources/aging for the black carbon and the physical mixing state as well as the sources for the short (a few minutes) increases in the aerosol loading and determine if the source for these is dust or sea salt or another source. We are also interested in comparing the black carbon we see here to samples collected during the agriculture burns in January/February and in comparing the larger particles to bioaerosols in the spring. To obtain these comparisons, we will need to collect more samples in the other seasons. Finally, we have some size-resolved particle collectors that can be deployed at the same time as the tethered balloon launches. We have discussed with Swarup China about trying to get the timing to work in August and we are interested in coordinating again later, if possible. This will give us ground-level and vertical aerosol mixing state sample sets that will be very exciting to analyze.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

An Ab Initio Electronic Structure Investigation of the Ground and Excited States of ScH + , YH + , and LaH +

Multireference configuration interaction (MRCI), Davidson-corrected MRCI (MRCI+Q), coupled-cluster singles, doubles, and perturbative triples [CCSD(T)], and frozen-core full configuration interaction (fcFCI) calculations were carried out using large, correlation-consistent basis sets to investigate the excited states of the Sc atom and the spin–free and spin–orbit coupled potential energy profiles, energetics, spectroscopic constants, and electron populations of low-lying states of MH + (M = Sc, Y, La). The core electron correlation effects, complete basis set effects, and spin–orbit coupling effects were also evaluated. The first four electronic states of all MH + are 1 2 Δ, 1 2 Σ + , 1 2 Π, and 2 2 Σ + with 1σ 2 1δ 1 , 1σ 2 2σ 1 , 1σ 2 1π 1 , and 1σ 2 3σ 1 single-reference electron configurations, respectively. These states of MH + can be represented by the M 2+ H – ionic structure. The ground states of ScH + , YH + , and LaH + are 1 2 Δ 3/2 , 1 2 Σ + 1/2 , and 1 2 Δ 3/2 with 55.45, 60.54, and 62.34 kcal/mol bond energies, respectively. The core electron correlation was found to be vital for gaining accurate predictions on the ground and excited state properties of MH + . The spin–orbit coupling effects are minor for ScH + but become substantial moving to YH + and LaH + . Overall, the results of this work are in good agreement with the limited set of experimental findings of MH + available in the literature and will be of use for future investigations. Furthermore, the theoretical approaches, findings, and trends reported here are expected to aid studies of similar species.

74 ATOMIC AND MOLECULAR PHYSICS↗