Search NASA⌕ Search

SEARCH · Search NASA

Results for “THRESHOLD SHIFT”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Revisiting the three-kaon interaction and its relation with 𝐾⁡(1460)

Here, we test the hypothesis of 𝐾⁡(1460) being a hadronic 𝐽 𝑃 = 0 − molecule through nonperturbative 𝑆-wave $KK\bar{⁢K}$, 𝐾⁢𝜋⁢𝜋, 𝐾⁢𝜋⁢𝜂 coupled-channel dynamics in a three-body unitary isobar approach. The scalar two-body coupled-channel resonances 𝑓 0 ⁡(500), 𝑓 0 ⁡(980), 𝑎 0 ⁡(980), and 𝐾$^*_0$⁡(700) are generated in the subsytems in amplitudes that match phase shifts from experiment. In a first step, previous results in the limit of mass-degenerate, stable 𝑓 0 and 𝑎 0 isobars are reproduced. Once the full seven-coupled channel model is switched on, other 𝑆-matrix effects obscure and modify the resonance signal, including complex thresholds, a two-body cusp, and a triangle singularity at threshold.

Döring, M. [George Washington Univ., Washington, D↗
DOE OSTI2024

Engineering exchange bias at the interface of self-polarized ultrathin ferroelectric Ba⁢Ti⁢O 3 and ferromagnetic La 0.67⁢ Sr 0.33 ⁢Mn⁢O 3

We investigate the emergence and optimization of conventional exchange bias (EB) in ultrathin (<10 nm) ferroelectric (FE) Ba⁢Ti⁢O 3 (BTO)/ferromagnetic (FM) La 0.67 ⁢Sr 0.33⁢ Mn⁢O 3 (LSMO) epitaxial bilayers without an antiferromagnetic (AFM) material. The EB originates from the electronic orbital reconstruction at the FE-FM interface due to the ferroelectric polarization. We achieve maximum EB of approximately 42 Oe with single-domain polarization in nine-unit-cell-thick BTO, setting the BTO thickness above the critical threshold for ferroelectricity yet below the thickness of strain relaxation and multidomain breakdown. Furthermore, the LSMO layer needs to be thick enough to sustain both the FM layer and polarization-induced AFM spin configuration at the LSMO/BTO interface, yet as thin as possible to enable the EB loop shift. The temperature, training, field, and thickness dependence of the EB confirm that the LSMO/BTO interface exhibits conventional EB despite its unconventional origin. Using x-ray magnetic circular dichroism, scanning transmission electron microscopy, and density-functional-theory calculations, we confirm that the macroscopic EB effect originates from the interfacial AFM spin configuration in LSMO driven by FE-induced d-orbital modifications in interfacial Mn ions. Thus, we engineer strong interfacial EB coupling in artificial multiferroics without a conventional AFM material by controlling FE polarization, highlighting the potential for advanced spintronic applications.

exchange bias↗
NASA NTRS1987

Quantification of the memory imprint effect for a charged particle environment

The effects of total accumulated dose on the single-event vulnerability of NMOS resistive-load SRAMs are investigated. The bias-dependent shifts in device parameters can imprint the memory state present during exposure or erase the imprinted state. Analysis of these effects is presented along with an analytic model developed for the quantification of these effects. The results indicate that the imprint effect is dominated by the difference in the threshold voltage of the n-channel devices.

Bhuva, B. L.↗
NASA NTRS1990

Stimulated Raman shifting of the Nd:YAG fourth harmonic (266 nm) in H2, HD, and D2

The dependence of the first Stokes stimulated Raman conversion efficiency of fourth-harmonic radiation from a Nd:YAG laser at 266 nm has been studied for the isotopic species H2, HD, and D2 as a function of gas pressure and laser energy using a low numerical aperture (about 0.0045) pumping geometry. While the laser energy threshold for first Stokes conversion varies significantly among the species, photon conversion efficiencies of at least 50 percent can be achieved for all of them for laser pump energies at 266 nm of 50 mJ/pulse or less. This study provides a new measurement of the differential cross section for stimulated Raman scattering in HD of 8.1 + or - 2.4 x 10 to the -29th sq cm/sr at 266 nm and at high pressures, and agreement is found with previous measurements of the cross sections for H2 and D2. The results have been used to optimize the laser transmitter system for a differential-absorption lidar to measure tropospheric ozone concentration profiles.

Haner, David A.↗
NASA NTRS2017

Correlation Between Soil Moisture and Dust Emissions: An Investigation for Global Climate Modeling

This work is using the newly available NASA SMAP soil moisture measurement data to evaluate its impact on the atmospheric dust emissions. Dust is an important component of atmospheric aerosols, which affects both climate and air quality. In this work, we focused on semi-desert regions, where dust emissions show seasonal variations due to soil moisture changes, i.e. in Sahel of Africa. We first identified three Aerosol Robotic Network (AERONET) sites in the Sahel (IER_Cinzana, Banizoumbou, and Zinder_Airport). We then utilized measurements of aerosol optical depth (AOD), fine mode fraction, size distribution, and single-scattering albedo and its wave-length dependence to select dust plumes from the available measurements We matched the latitude and longitude of the AERONET station to the corresponding SMAP data cell in the years 2015 and 2016, and calculated their correlation coefficient. Additionally, we looked at the correlation coefficient with a three-day and a five-day shift to check the impact of soil moisture on dust plumes with some time delay. Due to the arid nature of Banizoumbou and Zinder_Airport, no correlation was found to exist between local soil moisture and dust aerosol load. While IER_Cinzana had soil moisture levels above the satellite threshold of 0.02cm3/cm3, R-value approaching zero indicated no presence of a correlation. On the other hand, Ilorin demonstrated a significant negative correlation between aerosol optical depth and soil moisture. When isolating the analysis to Ilorin's dry season, a negative correlation of -0.593 was the largest dust-isolated R-value recorded, suggesting that soil moisture is driven the dust emission in this semi-desert region during transitional season.

climate↗
DOE OSTI2024

Molecularly Imprinted Polymer Sensor Empowered by Bound States in the Continuum for Selective Trace-Detection of TGF-beta

The integration of advanced materials and photonic nanostructures can lead to enhanced biodetection capabilities, crucial in clinical scenarios and point-of-care diagnostics, where simplified strategies are essential. Herein, a molecularly imprinted polymer (MIP) photonic nanostructure is demonstrated, which selectively binding to transforming growth factor-beta (TGF-β), in which the sensing transduction is enhanced by bound states in the continuum (BICs). The MIP operating as a synthetic antibody matrix and coupled with BIC resonance, enhances the optical response to TGF-β at imprinted sites, leading to an augmented detection capability, thoroughly evaluated through spectral shift and optical lever analogue readout. The validation underscores the MIP-BIC sensor capability to detect TGF-β in spiked saliva, achieving a limit of detection of 10 fM and a resolution of 0.5 pM at physiological concentrations, with a precision of two orders of magnitude above discrimination threshold in patients. The MIP tailored selectivity is highlighted by an imprinting factor of 52, showcasing the sensor resistance to interference from other analytes. The MIP-BIC sensor architecture streamlines the detection process eliminating the need for complex sandwich immunoassays and demonstrates the potential for high-precision quantification. This positions the system as a robust tool for biomarker detection, especially in real-world diagnostic scenarios.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Bottomonium suppression from the three-loop QCD potential

We compute the suppression of bottomonium in the quark-gluon plasma using the three-loop QCD static potential. The potential describes the spin-averaged bottomonium spectrum below threshold with a less than 1% error. Within potential nonrelativistic quantum chromodynamics and an open quantum systems framework, we compute the evolution of the bottomonium density matrix. The values of the quarkonium transport coefficients are obtained from lattice QCD measurements of the bottomonium in-medium width and thermal mass shift; we additionally include for the first time a vacuum contribution to the dispersive coefficient γ . Using the three-loop potential and the values of the heavy quarkonium transport coefficients, we find that the resulting bottomonium nuclear modification factor is consistent with experimental observations, while at the same time reproducing the lattice measurements of the in-medium width. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1990

Plasma waves associated with the space shuttle

Water molecules outgassed from the Space Shuttle suffer collisional charge-exchange with ionospheric oxygen ions, thereby forming unstable distributions of pick-up water ions and leading to high levels of plasma waves near the Shuttle. Liouville's equation with a charge-exchange source term is solved for the water ion distribution function as a function of position relative to the Shuttle. The observational characteristics of the near zone Shuttle waves are summarized. A linear theory in which beam like distributions of water ions drive Doppler shifted lower hybrid waves via the modified two stream instability is developed. This theory explains many characteristics of the near zone waves. Further work on the effects of wave nonlinearities and spatial inhomogeneity is required to explain the detailed frequency spectrum of the waves. The observed wave levels apparently satisfy the threshold condition for modulational instability of lower hybrid waves.

Cairns, I. H.↗
DOE OSTI2026

Uncertainty quantification and reliability assessment for intermodal freight transportation

Intermodal freight optimization models support cost-effective, low-emission, and timely goods movement by coordinating trucks, rail, and barges. These models determine optimal flows, routing, and modal switches while respecting infrastructure and operational constraints. However, their real-world utility is often undermined by pervasive uncertainties-such as fluctuating transportation costs and emissions, variable terminal capacities, and uncertain freight demand-that distort key performance outcomes, including total system cost, carbon footprint, and transit time reliability. This study presents a structured framework for quantifying uncertainty in intermodal freight transportation (IFT) optimization. The framework evaluates how input uncertainty affects system performance and reliability, a critical need for ensuring that model-based decisions remain robust under real-world variability, especially amid volatile fuel prices, shifting demand, and growing disruptions. It integrates three complementary methods: (1) Sobol-based global sensitivity analysis to identify influential parameters affecting cost, emissions, and transit time, (2) Monte Carlo-based capacity perturbation analysis to assess robustness under probabilistic facility disruptions, and (3) Monte Carlo filtering with Bayesian inference to detect threshold-based performance vulnerabilities. The results highlight diesel truck unit cost as the dominant driver of variability. To improve system resilience, planners should prioritize uncertainty in fuel-related parameters when designing intermodal strategies.

Intermodal freight transportation↗
NASA NTRS1989

Paradoxical monocular stereopsis and perspective vergence

The question of how to most effectively convey depth in a picture is a multifaceted problem, both because of potential limitations of the chosen medium (stereopsis, image motion), and because effectiveness can be defined in various ways. Practical applications usually focus on information transfer, i.e., effective techniques for evoking recognition of implied depth relationships, but this issue depends on subjective judgements which are difficult to scale when stimuli are above threshold. Two new approaches to this question are proposed here which are based on alternative criteria for effectiveness. Paradoxical monocular stereopsis is a remarkably compelling impression of depth which is evoked during one-eyed viewing of only certain illustrations; it can be unequivocally recognized because the feeling of depth collapses when one shifts to binocular viewing. An exploration of the stimulus properties which are effective for this phenomenon may contribute useful answers for the more general perceptual problem. Positive vergence is an eye-movement response associated with changes of fixation point within a picture which implies depth; it also arises only during monocular viewing. The response is directionally appropriate (i.e., apparently nearer objects evoke convergence, and vice versa), but the magnitude of the response can be altered consistently by making relatively minor changes in the illustration. The cross-subject agreement in changes of response magnitude would permit systematic exploration to determine which stimulus configurations are most effective in evoking perspective vergence, with quantitative answers based upon this involuntary reflex. It may well be that most effective pictures in this context will embody features which would increase effectiveness of pictures in a more general sense.

Enright, J. T.↗
NASA NTRS2009

Characteristics of Whipple Shield Performance in the Shatter Regime

Between the onset of projectile fragmentation and the assumption of rear wall failure due to an impulsive load, multi-wall ballistic limit equations are linearly interpolated to provide reasonable yet conservative predictions of perforation thresholds with conveniently simple mathematics. Although low velocity and hypervelocity regime predictions are based on analytical expressions, there is no such scientific foundation for predictions in the intermediate (or shatter) regime. As the debris flux in low earth orbit (LEO) becomes increasingly dominated by manmade pollution, the profile of micrometeoroid and orbital debris (MMOD) risk shifts continually towards lower velocities. For the International Space Station (ISS), encounter velocities below 7 km/s now constitute approximately 50% of the penetration risk. Considering that the transition velocity from shatter to hypervelocity impact regimes described by common ballistic limit equations (e.g. new non-optimum Whipple shield equation [1]) occurs at 7 km/s, 50% of station risk is now calculated based on failure limit equations with little analytical foundation. To investigate projectile and shield behavior for impact conditions leading to projectile fragmentation and melt, a series of hypervelocity impact tests have been performed on aluminum Whipple shields. In the experiments projectile diameter, bumper thickness, and shield spacing were kept constant, while rear wall thickness was adjusted to determine spallation and perforation limits at various impact velocities and angles. The results, shown in Figure 1 for normal and 45 impacts, demonstrated behavior that was not sufficiently described by the simplified linear interpolation of the NNO equation (also shown in Figure 1). Hopkins et al. [2] investigated the performance of a nominally-identical aluminum Whipple shield, identifying the effects of phase change in the shatter regime. The results (conceptually represented in Figure 2) were found to agree well with those obtained in this study at normal incidence, suggesting that shielding performance in the shatter regime could be well described by considering more complex phase conditions than currently implemented in most BLEs. Furthermore, evidence of these phase effects were found in the oblique test results, providing the basis for an empirical description of these effects that can be applied in MMOD risk assessment software. In this paper, results of the impact experiments are presented, and characteristics of target damage are evaluated. A comparison of intermediate velocity impact failure mechanisms in current BLEs are discussed and compared to the findings of the experimental study. Risk assessment calculations have been made on a simplified structure using currently implemented penetration equations and predicted limits from the experimental program, and the variation in perceived mission risk is discussed. It was found that ballistic limit curves that explicitly incorporated phase change effects within the intermediate regime lead to a decrease in predicted MMOD risk for ISS-representative orbits. When considered for all Whipple-based shielding configurations onboard the ISS, intermediate phase change effects could lead to significant variations in predicted mission risk.

Ryan, Shannon↗
DOE OSTI2026

Protonation Dynamics of Confined Ethanol–Water Mixtures in H-ZSM-5 from Machine Learning-Driven Metadynamics

Zeolites are indispensable heterogeneous catalysts in industrial chemical processes, valued for their strong Brønsted acidity, well-defined microporous frameworks, and tunable pore structures. Their catalytic activity arises primarily from Brønsted acid sites (BAS), typically present as bridging hydroxyl groups (Si–OH–Al). Under aqueous reaction conditions, these protons interact dynamically with water and alcohol molecules, leading to complex solvation and protonation behavior within confined pores. In this study, we investigate the protonation equilibrium occurring between ethanol and water at the BAS of acidic zeolites under varying hydration levels, i.e., C2H5OH–(H2O)n, n=1–4. Local structure was analyzed through an adaptive-learning global optimization algorithm, while enhanced sampling molecular dynamics simulations with Well-Tempered Metadynamics (WMetaD) and machine learning interatomic potentials (MLPs) provide free-energy surfaces (FES) at variable hydration levels. The results reveal a strong dependence of proton localization on the degree of hydration. At low hydration (1 water molecule), the proton resides predominantly on ethanol; with 2 water molecules, it shifts toward water, and at higher hydration (3 or more water molecules), it becomes extensively delocalized over the water cluster. These findings underscore the critical role of solvation in modulating acid site behavior and suggest that a minimum of three water molecules is necessary to fully stabilize the proton on water within the zeolite framework. This solvation threshold has significant implications for catalytic processes, particularly in biomass conversion reactions where alcohol protonation is a key step in dehydration mechanisms.

machine learning↗
NASA NTRS1992

Energy for lunar resource exploitation

Humanity stands at the threshold of exploiting the known lunar resources that have opened up with the access to space. America's role in the future exploitation of space, and specifically of lunar resources, may well determine the level of achievement in technology development and global economic competition. Space activities during the coming decades will significantly influence the events on Earth. The 'shifting of history's tectonic plates' is a process that will be hastened by the increasingly insistent demands for higher living standards of the exponentially growing global population. Key to the achievement of a peaceful world in the 21st century, will be the development of a mix of energy resources at a societally acceptable and affordable cost within a realistic planning horizon. This must be the theme for the globally applicable energy sources that are compatible with the Earth's ecology. It is in this context that lunar resources development should be a primary goal for science missions to the Moon, and for establishing an expanding human presence. The economic viability and commercial business potential of mining, extracting, manufacturing, and transporting lunar resource based materials to Earth, Earth orbits, and to undertake macroengineering projects on the Moon remains to be demonstrated. These extensive activities will be supportive of the realization of the potential of space energy sources for use on Earth. These may include generating electricity for use on Earth based on beaming power from Earth orbits and from the Moon to the Earth, and for the production of helium 3 as a fuel for advanced fusion reactors.

Glaser, Peter E.↗
DOE OSTI2023

Temperature-induced densification in compressed basaltic glass revealed by in-situ ultrasonic measurements

Abstract Acoustic velocities of a model basalt glass (64 mol% CaMgSi2O6 + 36 mol% CaAl2Si2O8) were measured along different pressure-temperature (P-T) paths. One set of experiments involved isothermal compression-decompression cycles, performed at temperatures of 300, 641, 823, and 1006 K and pressures up to 12.2 GPa. The other set of experiments involved constant-load heating-cooling cycles at temperatures up to 823 K and pressures up to 7.5 GPa. Both sets of experiments were performed in a multi-anvil apparatus using a synchrotron-based ultrasonic technique. Our results show that the glass compressed isothermally at 300 K (cold-compression) displays anomalously decreasing compressional (VP) and shear (VS) wave velocities with increasing pressure until ~8 GPa. Beyond 8 GPa, both VP and VS start to increase sharply with pressure and irreversible densification of the glass occurred, producing large hysteresis loops of velocities upon decompression. However, for the glass compressed isothermally at increasingly higher temperatures (hot-compression), the velocity minima gradually shift to lower pressures. At temperature close to the glass transition temperature Tg, the velocity minima disappear completely, displaying a monotonic increase of velocities during compression and higher VP and VS during decompression. In addition, constant-load heating-cooling experiments show that velocities generally decrease slightly with increasing temperature, but start to increase once heated above a threshold temperature (~650 K). During cooling the velocities increase almost linearly with decreasing temperature, resulting in higher velocities (~1.5–2.5% higher) when returned to 300 K. This implies that a temperature-induced densification may have occurred in the glass at high pressures. Raman spectra on recovered samples show that the hot-compressed and high-P heated glasses contain distinctly densified and depolymerized structural signatures compared to the initial glass and the cold-compressed glass below the velocity transition pressure PT (~8 GPa). Such densification may be attributed to the breaking of bridging oxygen bonds and compaction in the intermediate-range structure. Our results demonstrate that temperature can facilitate glass densification at high pressures and point out the importance of P-T history in understanding the elastic properties of silicate glasses. Comparison with melt velocity suggests that hot-compressed glasses may better resemble the pressure dependence of velocity of silicate melts than cold-compressed glasses, but still show significantly higher velocities than melts. If the abnormal acoustic behaviors of cold-compressed glasses were used to constrain melt fractions in the mantle low-velocity regions, the melt fractions needed to explain a given velocity reduction would be significantly underestimated at high pressures.

Geochemistry & Geophysics↗
NASA NTRS1988

Flight test results of a vector-based failure detection and isolation algorithm for a redundant strapdown inertial measurement unit

Flight test results of a vector-based fault-tolerant algorithm for a redundant strapdown inertial measurement unit are presented. Because the inertial sensors provide flight-critical information for flight control and navigation, failure detection and isolation is developed in terms of a multi-level structure. Threshold compensation techniques for gyros and accelerometers, developed to enhance the sensitivity of the failure detection process to low-level failures, are presented. Four flight tests, conducted in a commercial transport type environment, were used to determine the ability of the failure detection and isolation algorithm to detect failure signals, such a hard-over, null, or bias shifts. The algorithm provided timely detection and correct isolation of flight control- and low-level failures. The flight tests of the vector-based algorithm demonstrated its capability to provide false alarm free dual fail-operational performance for the skewed array of inertial sensors.

Morrell, F. R.↗
NASA NTRS2020

Use of Otoacousticemission Phase Change to Evaluate Countermeasures for Spaceflight-Associated Neuro-Ocular Syndrome

Spaceflight-associated neuro-ocular syndrome (SANS) is a human spaceflight risk recognized by NASA. Elevated intracranial pressure (ICP) has been implicated as a root cause of many SANS signs and symptoms, yet there is no reliable noninvasive means of monitoring ICP. We have developed a noninvasive method of monitoring ICP change that exploits ear canal acoustic and otoacoustic emission (OAE) measurements. Changed ICP alters pressure in the inner ear, leading to changes in the tension and position of middle ear (ME) components; tension of these components determines the phase of the stimulus in the ear canal and the OAE response sound transmission back through the ME. The OAE method has been validated in several studies, including our own experiments as part of the NASA Fluid Shifts study. Systematic OAE phase changes demonstrating increased ME tension (an ICP indicator) are observed as posture is changed from seated to supine to head-down tilt (HDT). This effect can be substantially mitigated by lower body negative pressure (LBNP). The OAE technique has also been used on International Space Station (ISS) crewmembers, providing evidence that ICP in microgravity is similar to that seen on the ground in the supine position. The OAE method is also a rapid and noninvasive means of assessing the effectiveness of SANS countermeasures. Here we report results from two studies which used OAEs. In the most recent study (Venous Congestion Countermeasures - VCCM), three promising countermeasures [LBNP, an impedance threshold device (ITD), and veno-occlusive thigh cuffs (VTC)] were applied individually and in combination. In our previous ITD-only study, ITD was investigated for its ability to reduce ICP and cephalic venous congestion in supine and various HDT postures. Internal jugular vein (IJV) ultrasound showed a clear decongestive effect at all postures, however OAE data showed that ITD only caused a phase decrease (tension decrease) in HDT postures. In supine, ITD appeared to INCREASE tension. This paradox leads us to hypothesize that the OAE method is not accurately representing ICP changes with countermeasures (CM), which can alter ME tension through other means, such as ME pressure (MEP) changes. More generally, the exact mechanism for observed OAE response and stimulus phase shifts are not clearly understood, specifically with regard to the effects of MEP. The VCCM study examined the effects of externally-applied MEP on OAE recordings to document the relationship between these parameters. Analysis of these data provide new insights to these OAE mechanisms, in addition to results on CM effectiveness.

Kemp, D.↗
DOE OSTI2024

Amplified Spontaneous Emission from Electron–Hole Quantum Droplets in Colloidal CdSe Nanoplatelets

Two-dimensional cadmium selenide nanoplatelets (NPLs) exhibit large absorption cross sections and homogeneously broadened band-edge transitions that offer utility in wide-ranging optoelectronic applications. Here, we examine the temperature-dependence of amplified spontaneous emission (ASE) in 4- and 5-monolayer thick NPLs and show that the threshold for close-packed (neat) films decreases with decreasing temperature by a factor of 2-10 relative to ambient temperature owing to extrinsic (trapping) and intrinsic (phonon-derived line width) factors. Interestingly, for pump intensities that exceed the ASE threshold, we find development of intense emission to lower energy in particular provided that the film temperature is <= 200 K. For NPLs diluted in an inert polymer, both biexcitonic ASE and low-energy emission are suppressed, suggesting that described neat-film observables rely upon high chromophore density and rapid, collective processes. Transient emission spectra reveal ultrafast red-shifting with the time of the lower energy emission. Taken together, these findings indicate a previously unreported process of amplified stimulated emission from polyexciton states that is consistent with quantum droplets and constitutes a form of exciton condensate. For studied samples, quantum droplets form provided that roughly 17 meV or less of thermal energy is available, which we hypothesize relates to polyexciton binding energy. Polyexciton ASE can produce pump-fluence-tunable red-shifted ASE even 120 meV lower in energy than biexciton ASE. Finally, our findings convey the importance of biexciton and polyexciton populations in nanoplatelets and show that quantum droplets can exhibit light amplification at significantly lower photon energies than biexcitonic ASE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗