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Results for “persistent current”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Formation and dynamics of large-scale magnetic structures in the ionosphere of Venus

The formation and dynamics of large-scale magnetic structures in the ionosphere of Venus are examined. It is shown that such structures must be the result of steady state convection of interplanetary field lines into the ionosphere by the small amount of solar wind plasma (less than or approximately equal to 1-5 percent) absorbed by the planetary atmosphere below the ionopause, rather than isolated remnants of large fields persisting for long periods without connection to the solar wind induced current and convection pattern. In particular, it is demonstrated that the magnetic diffusion of such structures would result in their dissipation with time scales of 1-10 min, if they were not steady state structures in convective and diffusive equilibriuim. It is shown that the equations governing the diffusion of these magnetic structures are similar to those governing diffusion of a gas out of an enclosed chamber with a porous wall, and a simple analog is illustrated. The application of these results to magnetic fields of astrophysical plasmas is discussed.

Cloutier, P. A.↗
NASA NTRS2006

The Role of Ring Current on Slot Region Penetration

During magnetic quiet times, the inner belt, slot region and the outer belt are well defined regions. However, during some major storms, outer belt particles penetrate inward and significantly fill the slot region. In some extreme events, the outer belt particles travel through the slot and create a new belt in the inner region that persists from months to years. In this paper, we examine the role of the ring current on this radiation belt penetration into the slot region. The storm-time intensification of the ring current produces strong magnetic depression in the inner magnetosphere. This perturbation and its fluctuation enhance the radial transport and diffusion of the outer radiation belt particles. We perform kinetic and test-particle calculations to quantitatively assess the effects of the ring current field on filling of the slot region. Simulation results during major storms will be presented and discussed.

Fok, Mei-Ching↗
NASA NTRS2007

Ocean-Atmosphere Interaction Over Agulhas Extension Meanders

Many years of high-resolution measurements by a number of space-based sensors and from Lagrangian drifters became available recently and are used to examine the persistent atmospheric imprints of the semi-permanent meanders of the Agulhas Extension Current (AEC), where strong surface current and temperature gradients are found. The sea surface temperature (SST) measured by the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and the chlorophyll concentration measured by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) support the identification of the meanders and related ocean circulation by the drifters. The collocation of high and low magnitudes of equivalent neutral wind (ENW) measured by Quick Scatterometer (QuikSCAT), which is uniquely related to surface stress by definition, illustrates not only the stability dependence of turbulent mixing but also the unique stress measuring capability of the scatterometer. The observed rotation of ENW in opposition to the rotation of the surface current clearly demonstrates that the scatterometer measures stress rather than winds. The clear differences between the distributions of wind and stress and the possible inadequacy of turbulent parameterization affirm the need of surface stress vector measurements, which were not available before the scatterometers. The opposite sign of the stress vorticity to current vorticity implies that the atmosphere spins down the current rotation through momentum transport. Coincident high SST and ENW over the southern extension of the meander enhance evaporation and latent heat flux, which cools the ocean. The atmosphere is found to provide negative feedback to ocean current and temperature gradients. Distribution of ENW convergence implies ascending motion on the downwind side of local SST maxima and descending air on the upwind side and acceleration of surface wind stress over warm water (deceleration over cool water); the convection may escalate the contrast of ENW over warm and cool water set up by the dependence of turbulent mixing on stability; this relation exerts a positive feedback to the ENW-SST relation. The temperature sounding measured by the Atmospheric Infrared Sounder(AIRS) is consistent with the spatial coherence between the cloud-top temperature provided by the International Satellite Cloud Climatology Project (ISCCP) and SST. Thus ocean mesoscale SST anomalies associated with the persistent meanders may have a long-term effect well above the midlatitude atmospheric boundary layer, an observation not addressed in the past.

Atmospheric Infrared Sounder (AIRS)↗
DOE OSTI2024

Shape-persistent ladder molecules exhibit nanogap-independent conductance in single-molecule junctions

Molecular electronic devices require precise control over the flow of current in single molecules. However, the electron transport properties of single molecules critically depend on dynamic molecular conformations in nanoscale junctions. Here, in this work, we report a unique strategy for controlling molecular conductance using shape-persistent molecules. Chemically diverse, charged ladder molecules, synthesized via a one-pot multicomponent ladderization strategy, show a molecular conductance (d[log( G/G 0 )]/d x ≈ -0.1 nm -1 ) that is nearly independent of junction displacement, in stark contrast to the nanogap-dependent conductance (d[log( G/G 0 )]/d x ≈ -7 nm -1 ) observed for non-ladder analogues. Ladder molecules show an unusually narrow distribution of molecular conductance during dynamic junction displacement, which is attributed to the shape-persistent backbone and restricted rotation of terminal anchor groups. These principles are further extended to a butterfly-like molecule, thereby demonstrating the strategy's generality for achieving gap-independent conductance. Overall, our work provides important avenues for controlling molecular conductance using shape-persistent molecules. Achieving robust and controllable conductance in single-molecule junctions is challenging due to the dynamic nature of molecular conformations that fluctuate over operational timescales. A strategy using shape-persistent molecules has now been developed that demonstrates nearly junction-displacement-independent conductance, providing a stable solution for single-molecule electronic properties.

molecular electronics↗
NASA NTRS1993

The equatorial electrojet and associated currents as seen in Magsat data

In view of the disagreement between reports of Langel and Estes (1985) and those of other investigators using Nagsat data sets, concerning the evidence for equatorial electrojet and meridional currents in the dawn Magsat data, this paper reexamines the Magsat data for the presence of equatorial electrojet and meridional current in both dawn and dusk local times, using a specially designed method for isolating field variations organized by dip-latitude. It is shown that such fields, if any, at dawn are very weak and do not result in a persistent pattern from longitude to longitude or a pattern consistent with that expected from an electrojet current. On the other hand, fields organized by dip-latitude are clearly present in the dusk data and it is possible to isolate longitudinal and seasonal variations in such fields. Current densities are computed for both the equatorial electrojet and meridional currents and are compared to the current densities and distributions found with recent models of the ionospheric dynamo and equatorial electrojet.

Langel, R. A.↗
DOE OSTI2023

Worth More Dead than Alive? Quantifying Necromass Persistence for Terrestrial Carbon Storage

The continuous cycle of plant-associated microbial biomass growth, death, and decay provides a consistent supply of necromass-C throughout the rooting zone of the soil profile. These inputs are obviously important for resource allocation and soil quality, but microbial necromass-C may play a critical, but currently unknown, role in mitigating the impacts of climate change through atmospheric decarbonization. Microbial necromass is the largest terrestrial sink of persistent carbon in soils, thus its fate and preservation will have a major impact on global C budgets. Our current understanding of the ecosystem controls on necromass generation, biogeochemical transformation, and stabilization is lacking. The objective of this project is to explore the specific influence of rhizosphere and necromass inputs on soil carbon pools.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2018

System Applications Software Development and Testing for the Spaceport Command and Control System

Known as "America's Spaceport," one of Kennedy Space Center's (KSC) primary responsibilities is the successful preparation for and launch of rockets into space. KSC's Engineering Software Branch has been tasked with creating a new command and control system that will provide check-out and launch control for future rockets and spacecraft. While work on the software began several years ago, development is ongoing and the operators who use the software on a daily basis have requested several features to improve their user experience. My internship in the fall of 2018 involved developing the source code and unit tests for two of these requested features: "Display Data with Persistence" (DDP) and "Save Events Button" (SEB). DDP's primary goal is to aid with ergonomics. Currently, users must press-and-hold on the mouse button to display information about points on a data plot. Once DDP is integrated, users will have the ability to double-click on a data plot to display that same information with persistence. Independent from DDP, the SEB provides users the ability to take information about different events that occur in the control system and save that data into a simple Comma Separated File (.csv) file format for easier analysis at a future time.

Niemoeller, Samantha↗
DOE OSTI2021

Timing Value of Marine Renewable Energy Resources for Potential Grid Applications

In this paper, the applicability of marine renewable energy for potential grid applications is presented. We show that many of the unique value streams from marine-based electricity generation stem from their inherent temporal characteristics, especially when compared to wind and solar. Specifically, in this work, we evaluate the timing value for three types of marine energy resources - (a) tidal (b) wave and (c) ocean currents. Firstly, through a suite of novel metrics such as resource availability, persistence and versatility, we evaluate the temporal value characteristics of these resources. Secondly, through a more grid-oriented numerical study, we comment on the potential ramifications of those temporal characteristics in context of energy balancing and effective load carrying capability, for one marine-based resource i.e. wave. Subsequently, we further our understanding of the relative advantages which may be leveraged by operating wave-based generation resources in tandem with more established renewable choices, such as solar and wind. Our results indicate that compared to wind and solar, marine energy resources are consistently more available and persistent on an hourly level, throughout an entire year of operation. In addition to this, wave resources are also seen to reduce both the magnitudes and the degree of volatility in balancing requirements within the power system. Our work not only focuses on sites specific to the Unites States (US), but also includes a parallel study for a location in Great Britain (GB). Results are found to be consistent for sites in both the US and GB, implying that the grid benefits discussed in this work could apply to a number of locations globally.

Bhattacharya, Saptarshi↗
DOE OSTI2022

Electrical Gating of the Charge-Density-Wave Phases in Two-Dimensional h -BN/1T-TaS 2 Devices

Here we report on the electrical gating of the chargedensity- wave phases and current in h-BN-capped three-terminal 1T-TaS 2 heterostructure devices. It is demonstrated that the application of a gate bias can shift the source–drain current– voltage hysteresis associated with the transition between the nearly commensurate and incommensurate charge-density-wave phases. The evolution of the hysteresis and the presence of abrupt spikes in the current while sweeping the gate voltage suggest that the effect is electrical rather than self-heating. We attribute the gating to an electric-field effect on the commensurate charge-density-wave domains in the atomic planes near the gate dielectric. The transition between the nearly commensurate and incommensurate charge-density-wave phases can be induced by both the source– drain current and the electrostatic gate. Since the charge-densitywave phases are persistent in 1T-TaS 2 at room temperature, one can envision memory applications of such devices when scaled down to the dimensions of individual commensurate domains and few-atomic plane thicknesses.

2D van der Waals materials↗
DOE OSTI2020

Metabolic Response in Patients With Post-treatment Lyme Disease Symptoms/Syndrome

Abstract Background Post-treatment Lyme disease symptoms/syndrome (PTLDS) occurs in approximately 10% of patients with Lyme disease following antibiotic treatment. Biomarkers or specific clinical symptoms to identify patients with PTLDS do not currently exist and the PTLDS classification is based on the report of persistent, subjective symptoms for ≥6 months following antibiotic treatment for Lyme disease. Methods Untargeted liquid chromatography–mass spectrometry metabolomics was used to determine longitudinal metabolic responses and biosignatures in PTLDS and clinically cured non-PTLDS Lyme patients. Evaluation of biosignatures included (1) defining altered classes of metabolites, (2) elastic net regularization to define metabolites that most strongly defined PTLDS and non-PTLDS patients at different time points, (3) changes in the longitudinal abundance of metabolites, and (4) linear discriminant analysis to evaluate robustness in a second patient cohort. Results This study determined that observable metabolic differences exist between PTLDS and non-PTLDS patients at multiple time points. The metabolites with differential abundance included those from glycerophospholipid, bile acid, and acylcarnitine metabolism. Distinct longitudinal patterns of metabolite abundance indicated a greater metabolic variability in PTLDS versus non-PTLDS patients. Small numbers of metabolites (6 to 40) could be used to define PTLDS versus non-PTLDS patients at defined time points, and the findings were validated in a second cohort of PTLDS and non-PTLDS patients. Conclusions These data provide evidence that an objective metabolite-based measurement can distinguish patients with PTLDS and help understand the underlying biochemistry of PTLDS.

Immunology↗
NASA NTRS1998

Sea Ice on the Southern Ocean

Year-round satellite records of sea ice distribution now extend over more than two decades, providing a valuable tool to investigate related characteristics and circulations in the Southern Ocean. We have studied a variety of features indicative of oceanic and atmospheric interactions with Antarctic sea ice. In the Amundsen & Bellingshausen Seas, sea ice extent was found to have decreased by approximately 20% from 1973 through the early 1990's. This change coincided with and probably contributed to recently warmer surface conditions on the west side of the Antarctic Peninsula, where air temperatures have increased by approximately 0.5 C/decade since the mid-1940's. The sea ice decline included multiyear cycles of several years in length superimposed on high interannual variability. The retreat was strongest in summer, and would have lowered the regional mean ice thickness, with attendant impacts upon vertical heat flux and the formation of snow ice and brine. The cause of the regional warming and loss of sea ice is believed to be linked to large-scale circulation changes in the atmosphere and ocean. At the eastern end of the Weddell Gyre, the Cosmonaut Polyna revealed greater activity since 1986, a recurrence pattern during recent winters and two possible modes of formation. Persistence in polynya location was noted off Cape Ann, where the coastal current can interact more strongly with the Antarctic Circumpolar Current. As a result of vorticity conservation, locally enhanced upwelling brings warmer deep water into the mixed layer, causing divergence and melting. In the Ross Sea, ice extent fluctuates over periods of several years, with summer minima and winter maxima roughly in phase. This leads to large interannual cycles of sea ice range, which correlate positively with meridinal winds, regional air temperatures and subsequent shelf water salinities. Deep shelf waters display considerable interannual variability, but have freshened by approximately 0.03/decade since the late 1950's. That could have slowed the thermohaline circulation beneath the Ross Ice Shelf and the properties or volume of local bottom water production.

Jacobs, Stanley S.↗
NASA NTRS2017

Risk Of Early Onset Osteoporosis Due To Spaceflight

Bone minerals decline in microgravity, and bone mineral density (BMD) losses of approximately -1 to -1.5% per month were calculated for astronauts serving on long-duration missions prior to 2009. It is unclear whether BMD losses will stabilize with time in space, or continue to diminish with time. In addition, it is unknown if fractional gravity, present on the moon and Mars, will mitigate the mineral loss. Clinicians diagnose osteoporosis in premenopausal females and males younger than 50 years on the basis of BMD T-scores < -2.5 (hip and lumbar spine) accompanied by clinical evidence of a fragility fracture. If mission-related changes to the skeleton cannot be corrected by rehabilitation after the mission, crewmembers could be at risk for premature osteoporosis-related fractures in later life. To mitigate this risk it is necessary to understand the dynamics underlying the BMD changes that occur in microgravity, to monitor for the persistence of changes after space flight, and to evaluate if and how current and future osteoporosis treatments might be used to mitigate the risk of long-term skeletal problems in astronauts.

Sibonga, Jean↗
DOE OSTI2021

Large ecosystem-scale effects of restoration fail to mitigate impacts of land-use legacies in longleaf pine savannas

Ecological restoration is a global priority, with potential to reverse biodiversity declines and promote ecosystem functioning. Yet, successful restoration is challenged by lingering legacies of past land-use activities, which are pervasive on lands available for restoration. Although legacies can persist for centuries following cessation of human land uses such as agriculture, we currently lack understanding of how land-use legacies affect entire ecosystems, how they influence restoration outcomes, or whether restoration can mitigate legacy effects. Using a large-scale experiment, we evaluated how restoration by tree thinning and land-use legacies from prior cultivation and subsequent conversion to pine plantations affect fire-suppressed longleaf pine savannas. In this work, we evaluated 45 ecological properties across four categories: 1) abiotic attributes, 2) organism abundances, 3) species diversity, and 4) species interactions. The effects of restoration and land-use legacies were pervasive, shaping all categories of properties, with restoration effects roughly twice the magnitude of legacy effects. Restoration effects were of comparable magnitude in savannas with and without a history of intensive human land use; however, restoration did not mitigate numerous legacy effects present prior to restoration. As a result, savannas with a history of intensive human land use supported altered properties, especially related to soils, even after restoration. The signature of past human land-use activities can be remarkably persistent in the face of intensive restoration, influencing the outcome of restoration across diverse ecological properties. Understanding and mitigating land-use legacies will maximize the potential to restore degraded ecosystems.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2023

Kinetic Effects of Anion Clusters on the Interfacial Stability between Solid-State Electrolyte and Metal Anode

The success of all-solid-state batteries (ASSBs) depends on the solid-state electrolyte (SSE) exhibiting high interfacial stability and room-temperature ionic conductivity. However, the current SSEs, especially those with practical ionic conductivities (≥10 –3 S/cm) at room temperature, often develop unstable interfaces at the metal anode, in some cases with even greater severity than with liquid organic electrolytes. Despite persistent efforts, achieving interfacial stability and sufficient ionic conductivity simultaneously represents one of the greatest challenges in ASSBs. The current approaches focus on stabilizing the interface by incorporating secondary interlayers or introducing coatings by surface engineering. The method is often material-specific, and the added interlayers often deteriorate during cycling. In this work, using phase analysis and explicit interface modeling, we demonstrate a strategy to kinetically stabilize the interface between the SSE and metal anode by incorporating selected monoanion clusters in the SSE; they can effectively lower or even halt the reduction kinetics at the interface by promoting on-site formation of interphases that are highly electron insulating. The study provides insight into the kinetic effects to achieve SSEs with superior properties in bulk and at the interface.

25 ENERGY STORAGE↗
NASA NTRS1986

Global ozone minima in the historical record

The magnitude and structure of the global total ozone minimum between 1958 and 1962 is similar to that observed between 1979 and 1983. Analysis of the single station data that exhibit the most pronounced minima suggest that the spatial structure of the global minimum is different from the currently observed reduction. Very low north polar values were observed, but there is no indication of anomalously low ozone in Antarctica. The temporal relationship to the sun spot cycle is similar in both time periods. Rather than solar terrestrial interaction, however, a more likely explanation of the early 1960's reduction is normal climatology caused by a persistent period of planetary wave activity. Such a natural explanation may also be appropriate for the current depletion.

Rood, Richard B.↗
DOE OSTI2025

Environmental life cycle of fentanyl: From the cradle to an unknown grave

The lack of available information on the presence and persistence of fentanyl in the environment is a significant gap in the technical literature. Although the origins of the opioid in the environment are well-known because they follow the same pathways of other drug-related environmental contaminants, the downstream effects of fentanyl in the water supply and its retention in soil are less understood. The characterization of fentanyl and its potential degradation products in complex environmental samples such as soil is severely understudied. Very few articles are available that work to identify fentanyl and its degradation products in complex samples or name the possible hazards that may result from environmental exposure and degradation. Therefore, the objectives were to identify available articles focused on environmental fentanyl and its pathways and highlight quantifiable research or results that included specific degradation products or downstream effects. Research articles focused on fentanyl between 2000 and 2024 were identified and reviewed and then filtered using Boolean search terms for environmental parameters. Various studies have determined that trace levels of fentanyl can be found in a variety of environments, and additional data suggest preferential partitioning into soils from water and long-term persistence. Despite this knowledge, very little data exists on the long-term downstream effects of fentanyl or its analogs. As the chronic effects from low-level fentanyl exposure are currently unknown, this lack of insight brings to the forefront the need for further research to improve our understanding of fentanyl persistence, degradation, and toxicity within the environment.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Large Local Currents in a Lithium-Ion Battery during Rest after Fast Charging

Increasing electric vehicle (EV) adoption requires lithium-ion batteries that can be charged quickly and safely. Some EV batteries have caught on fire despite being neither charged nor discharged. While the lithium that plates on graphite during fast charging affects battery safety, so do the internal ionic currents that can occur when the battery is at rest after charging. These currents are difficult to quantify; the external current that can readily be measured is zero. Here we study a graphite electrode at rest after 6C fast charging using operando X-ray microtomography. We quantify spatially resolved current density distributions that originate at plated lithium and end in underlithiated graphite particles. The average current densities decrease from 1.5 to 0.5 mA cm -2 in about 20 min after charging is stopped. Surprisingly, the range of the stripping current density is independent of time, with outliers above 20 mA cm -2 . In conclusion, the persistence of outliers provides a clue as to the origin of catastrophic failure in batteries at rest.

25 ENERGY STORAGE↗