Search NASA⌕ Search

SEARCH · Search NASA

Results for “persistent”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Persistent Expression Changes of Fibrosis Related Genes in the Lung Tissues of Rats Exposed to Lunar Dust Particles

The Moon's surface is covered by a layer of reactive dust, containing 1-2% of respirable fine dust (< 3 microns). The habitable area of any lunar landing vehicle would inevitably be contaminated with lunar dust that could pose a health risk. The purpose of the study is to evaluate the toxicity of Apollo moon dust in rodents through inhalation to assess the health risk of dust exposures to humans and to identify the mechanisms and potential pathways involved in lunar dust-induced toxicity. Ccl3, Ccl12, Cxcl2, Cxcl5, Itgb8, Tnf, Ldhc, Clec4e, Bmp7, and Smad6, showed persistently significant expression changes in the lung tissue. The expression of several of these genes were dose- and time- dependent, and were significantly correlated with other pathological. Our previous data showed that no pathological changes were detected in low dose groups. However, several genes, primarily produced by lung epithelial, were significantly altered persistently in response to low-dose dust exposure. The data presented in this study, for the first time, explores the molecular mechanisms of lunar dust induced toxicity, contributing not only the risk assessment for future space exploration, but also understandings of the dust-induced toxicity to humans on earth.

Zhang, Ye↗
NASA NTRS2013

Influence of Persistent Wind Scour on the Surface Mass Balance of Antarctica

Accurate quantification of surface snow accumulation over Antarctica is a key constraint for estimates of the Antarctic mass balance, as well as climatic interpretations of ice-core records. Over Antarctica, near-surface winds accelerate down relatively steep surface slopes, eroding and sublimating the snow. This wind scour results in numerous localized regions (< or = 200 sq km) with reduced surface accumulation. Estimates of Antarctic surface mass balance rely on sparse point measurements or coarse atmospheric models that do not capture these local processes, and overestimate the net mass input in wind-scour zones. Here we combine airborne radar observations of unconformable stratigraphic layers with lidar-derived surface roughness measurements to identify extensive wind-scour zones over Dome A, in the interior of East Antarctica. The scour zones are persistent because they are controlled by bedrock topography. On the basis of our Dome A observations, we develop an empirical model to predict wind-scour zones across the Antarctic continent and find that these zones are predominantly located in East Antarctica. We estimate that approx. 2.7-6.6% of the surface area of Antarctica has persistent negative net accumulation due to wind scour, which suggests that, across the continent, the snow mass input is overestimated by 11-36.5 Gt /yr in present surface-mass-balance calculations.

Antarctica↗
NASA NTRS2016

Persistence Mapping Using EUV Solar Imager Data

We describe a simple image processing technique that is useful for the visualization and depiction of gradually evolving or intermittent structures in solar physics extreme-ultraviolet imagery. The technique is an application of image segmentation, which we call "Persistence Mapping," to isolate extreme values in a data set, and is particularly useful for the problem of capturing phenomena that are evolving in both space and time. While integration or "time-lapse" imaging uses the full sample (of size N ), Persistence Mapping rejects (N - 1)/N of the data set and identifies the most relevant 1/N values using the following rule: if a pixel reaches an extreme value, it retains that value until that value is exceeded. The simplest examples isolate minima and maxima, but any quantile or statistic can be used. This paper demonstrates how the technique has been used to extract the dynamics in long-term evolution of comet tails, erupting material, and EUV dimming regions.

Thompson, B. J.↗
NASA NTRS2018

Persistence of Gamma-H2AX Foci in Irradiated Bronchial Cells Correlates with Susceptibility to Radiation Associated Lung Cancer in Mice

The risk of developing radiation-induced lung cancer differs between different strains of mice, but the underlying cause of the strain differences is unknown. Strains of mice also differ in their ability to efficiently repair DNA double strand breaks resulting from radiation exposure. We phenotyped mouse strains from the CcS/Dem recombinant congenic strain set for their efficacy in repairing DNA double strand breaks during protracted radiation exposures. We monitored persistent gamma-H2AX radiation induced foci (RIF) 24 hours after exposure to chronic gamma-rays as a surrogate marker for repair deficiency in bronchial epithelial cells for 17 of the CcS/Dem strains and the BALB/cHeN founder strain. We observed a very strong correlation R2 = 79.18%, P < 0.001) between the level of persistent RIF and radiogenic lung cancer percent incidence measured in the same strains. Interestingly, spontaneous levels of foci in non-irradiated strains also showed good correlation with lung cancer incidence (R2=32.74%, P =0.013). These results suggest that genetic differences in DNA repair capacity largely account for differing susceptibilities to radiation-induced lung cancer among CcS/Dem mouse strains and that high levels of spontaneous DNA damage is also a relatively good marker of cancer predisposition. In a smaller pilot study, we found that the repair capacity measured in peripheral blood leucocytes also correlated well with radiogenic lung cancer susceptibility, raising the possibility that such phenotyping assay could be used to detect radiogenic lung cancer susceptibility in humans.

Ochola, Donasian O.↗
NASA NTRS2018

System and Method for Providing a Climate Data Persistence Service

A system, method and computer-readable storage devices for providing a climate data persistence service. A system configured to provide the service can include a climate data server that performs data and metadata storage and management functions for climate data objects, a compute-storage platform that provides the resources needed to support a climate data server, provisioning software that allows climate data server instances to be deployed as virtual climate data servers in a cloud computing environment, and a service interface, wherein persistence service capabilities are invoked by software applications running on a client device. The climate data objects can be in various formats, such as International Organization for Standards (ISO) Open Archival Information System (OAIS) Reference Model Submission Information Packages, Archive Information Packages, and Dissemination Information Packages. The climate data server can enable scalable, federated storage, management, discovery, and access, and can be tailored for particular use cases.

Schnase, John L.↗
NASA NTRSDate not supplied

Seed surface sanitization and persistence of E.coli through different tissues of ‘Red Robin’ Tomato (Solanum lycopersicum cv. Red Robin)

Seed surface sanitization via chemical processes removes/reduces microbes from the external surfaces of the seed and thereby could have an impact on the plants’ health or productivity. To determine the impact of seed surface sanitization on the plants’ microbiome, sanitized and unsanitized seeds from ‘Red Robin’ Tomato (Solanumlycopersicum cv. Red Robin) were exposed to Escherichia coli (E. coli) and grown in a controlled environment growth chamber simulating environmental conditions aboard the International Space Station (ISS). Plants were harvested at four intervals, days 11, 33,42 and 76 post-germination. Changes in the microbial communities of leaf, stem, root, and fruit because of E. coli exposure and the persistence of E. coli itself were investigated using aerobic plate count (APC), qPCR and 16S rRNA sequencing. It was determined that E. coli persisted for longer periods of time in plants from sanitized versus unsanitized seeds and was identified in root tissue more frequently than in leaf or stem tissue. E. coli was not detected in fruits raised from either sanitized or unsanitized seeds. The 16S rRNA sequencing showed dynamic changes in the abundance of members of the phylum Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes in all tissue types studied. We observed minimal or no changes in the alpha diversity of leaf stem and fruit tissue with time, or between sanitized and unsanitized seeds. Roots showed significant differences in alpha diversity with time and seed sanitization status. Beta-diversity showed that time had more of an influence on all samples versus the E. coli treatment. Members of phyla Proteobacteria and Bacteroidetes were found to be differentially abundant across leaf, stem and root tissue. Our results indicated that the seed surface sanitization, although a requirement for sending seeds to space, might influence the developing microbiome. This research was funded by NASA’s Space Life and Physical Sciences Research and Applications.

Anirudha R Dixit↗
NASA NTRS1995

Exponential Convergence of the Tracking Error in Adaptive Systems Without Persistent Excitation

Persistent excitation conditions which ensure parameter convergence in adaptive algorithms have been studied by many researchers. Here, conditions are investigated for exponential convergence of the tracking error in feedforward adaptive systems without persistent excitation. Particular attention is paid to the continuous-time LMS algorithm in the overparametrized case. Results are presented.

control↗
NASA NTRS2019

Directional limits on persistent gravitational waves using data from Advanced LIGO’s first two observing runs

We perform an unmodeled search for persistent, directional gravitational wave (GW) sources using data from the first and second observing runs of Advanced LIGO. We do not find evidence for any GW signals. We place limits on the broadband GW flux emitted at 25 Hz from point sources with a power law spectrum at F(α;Θ) < (0.05–25) × 10^(−8) erg/sq. cmsHz and the (normalized) energy density spectrum in GWs at 25 Hz from extended sources at Ω(α)(Θ) < (0.19–2.89) × 10^(−8) per sr where α is the spectral index of the energy density spectrum. These represent improvements of 2.5–3× over previous limits. We also consider point sources emitting GWs at a single frequency, targeting the directions of Sco X-1, SN 1987A, and the Galactic center. The best upper limits on the strain amplitude of a potential source in these three directions range from h(0) < (3.6–4.7) × 10^(−25), 1.5× better than previous limits set with the same analysis method. We also report on a marginally significant outlier at 36.06 Hz. This outlier is not consistent with a persistent gravitational-wave source as its significance diminishes when combining all of the available data.

B. P. Abbott↗
NASA NTRSDate not supplied

Towards Persistent Space Observations through Autonomous Multi-Agent Formations

Sensing platforms must advance in scale and sophistication in order to support increasingly ambitious missions across Earth and space science; intelligence, surveillance, and reconnaissance (ISR); and planetary exploration. Distributed, persistent observation platforms have the potential to play a pivotal role in next generation missions through improved area coverage, enhanced situational awareness, and faster identification of trends and changes. The Multi-Agent Clusters for Persistent Observations from Space (MACPOS) project at NASA Langley Research Center is developing key technologies for the autonomous, heterogeneous formations that will comprise such platforms. Research thrusts include dynamic formation negotiation for self-assembling clusters of agents, distributed motion planning, and coordinated trajectory execution. Adaptive leader-follower formation negotiation allows agents to cluster and break off as necessary to adapt to both nominal and new mission objectives. Coordinated motion planning and execution maintain the formation while ensuring safe separation distances among agents and obstacles in the environment. These capabilities align MACPOS with NASA’s initiative for space and surface in-situ assembly through fundamental technology development for autonomous multi-agent systems. This paper presents an overview and early progress for the MACPOS project. We describe the system architecture for both individual agents and the overall fleet. Design considerations are given for the planning, control, and metrology subsystems. Finally, we discuss planned project milestones and the expected course of development.

Matthew P Vaughan↗
NASA NTRS2022

Persistent Layers of Enhanced Gravity Wave Dissipation in the Upper Mesosphere Revealed From SABER Observations

Dissipation of gravity waves (GWs) and resultant momentum flux deposition and eddy diffusion significantly influence the atmospheric structure and circulation. Using the temperature profiles measured by the SABER instrument (2002–2021), we derive the global GW action and its scale height (HAm). Comparing to the background scale height (H), we identify a persistent layer of enhanced GW dissipation (HAm/H > 2) in the upper mesosphere. The enhanced dissipation is primarily centered at 80–85 km with a vertical range of ∼8–20 km. At middle and high latitudes, the enhanced dissipation extends down to ∼60 km and is located above the eastward (westward) wind peak in winter (summer). At low latitudes, enhanced dissipation occurs around the wind reversals. The possible mechanisms of enhanced dissipation include wave refraction, wind filtering, and reduced static stability. The persistent layer of enhanced dissipation identified here provide observational evidence for GW dissipation constrains in models.

gravity waves↗
NASA NTRS2023

Impact of COVID-19-related Air Traffic Reductions on the Coverage and Radiative Effects of Linear Persistent Contrails over Conterminous United States and Surrounding Oceanic Routes

The radiative effects of the large-scale air traffic slowdown during Apr and May 2020 due to the international response to the COVID-19 pandemic are estimated by comparing the coverage (CC), optical properties, and radiative forcing of persistent linear contrails over the conterminous United States and two surrounding oceanic air corridors during the slowdown period and a similar baseline period during 2018 and 2019 when air traffic was unrestricted. The detected CC during the slowdown period decreased by an area-averaged mean of 41% for the three analysis boxes. The retrieved contrail optical properties were mostly similar for both periods. Total shortwave contrail radiative forcings during the slowdown were 34 and 42% smaller for Terra and Aqua, respectively. The corresponding differences for longwave contrail radiative forcing were 33% for Terra and 40% for Aqua. To account for the impact of any changes in the atmospheric environment between baseline and slowdown periods on detected CC amounts, the contrail formation potential (CFP) was computed from reanalysis data. In addition, a filtered CFP (fCFP) was also developed to account for factors that may affect contrail formation and visibility of persistent contrails in satellite imagery. The CFP and fCFP were combined with air traffic density data to create empirical models that estimated CC during the baseline and slowdown periods and were compared to the detected CC. The models confirm that decreases in CC and radiative forcing during the slowdown period were mostly due to the reduction in air traffic, and partly due to environmental changes.

contrails↗
NASA NTRSDate not supplied

Effect of Micrometeoroid and Orbital Debris Impact on Modal Response of Persistent Assets

Protecting the infrastructure and payload components of persistent assets (PAs) from damage caused by MicroMeteoroid and/or Orbital Debris (MMOD) impacts is a significant design consideration. The impact resistance to MMOD will need to be provided by the robustness of the structural configuration such that the asset does not suffer loss of function or catastrophic failure. Finite element modelling (FEM) can be used to investigate the effects of MMOD impact on the overall structural behavior of the PA. The models are being used here to investigate the structural response to ‘missing’ truss members, and parametric studies are being performed to identify the worst-case scenario of an impact catastrophically damaging a truss element. These models will be used to determine which truss members are the most critical to the structural performance, and thus, which may require a higher degree of protection or robustness to ensure they can withstand an MMOD impact without causing catastrophic effects on the entire structure. Initial results have been generated indicating a reduction in the global frequency due to missing truss members as a result of MMOD impact.

in-space assembly (ISA)↗
NASA NTRS2013

RXJ0440.9+4431: a Persistent Be-x-ray Binary in Outburst

The persistent Be/X-ray binary RXJ0440.9+4431 flared in 2010 and 2011 and has been followed by various X-ray facilities (Swift, RXTE, XMM-Newton, and INTEGRAL).We studied the source timing and spectral properties as a function of its X-ray luminosity to investigate the transition from normal to flaring activity and the dynamical properties of the system. We have determined the orbital period from the long-term Swift/BAT light curve, but our determinations of the spin-period are not precise enough to constrain any orbital solution. The source spectrum can always be described by a bulk-motion Comptonization model of black body seed photons attenuated by a moderate photoelectric absorption. At the highest luminosity, we measured a curvature of the spectrum, which we attribute to a significant contribution of the radiation pressure in the accretion process. This allows us to estimate that the transition from a bulk-motion-dominated flow to a radiatively dominated one happens at a luminosity of approx 2 × 10(exp 36) erg/ s. The luminosity dependency of the size of the black body emission region is found to be r(sub BB) varies as L(sub x) (exp 0.39 +/- 0.02). This suggests that either matter accreting onto the neutron star hosted in RXJ0440.9+4431 penetrates through closed magnetic field lines at the border of the compact object magnetosphere or that the structure of the Neutron star magnetic field is more complicated than a simple dipole close to the surface.

binary↗
NASA NTRSDate not supplied

NASA/EOSDIS Persistent Identifier Implementation

This presentation briefly summarizes the NASA Earth Science Data & Information Systems (ESDIS) Project’s approach to persistent identifiers for Earth science data sets and documentation in the Earth Observing System Data & Information System (EOSDIS). It briefly summarizes the ESDIS Project’s policies, and implementation approach, using Digital Object Identifiers.

Persistent Identifiers↗
NASA NTRSDate not supplied

NASA/EOSDIS Persistent Identifiers Status Update

This presentation summarizes the current status of NASA/Earth Observing System Data & Information System (EOSDIS) Digital Object Identifiers (DOIs) which provide Persistent Identifiers for citing NASA data sets.

Persistent Identifiers↗
NASA NTRSDate not supplied

On-orbit Servicing, Assembly and Manufacturing (OSAM) Near-Term in-Space Developmental Test Persistent Platform: ESPA-Star Based Implementation

Roundtable Session on In-Space Developmental Test: Springboard for Rapid Development. Presentation is a brief description of the On-orbit Servicing Assembly & Manufacturing (OSAM) national initiative & using standard EELV Secondary Payload Adapters (ESPAs) as the core building block to construct an ESPA-Star based implementation for an iSDT persistent platform in space.

Persistent Platform↗