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

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Fatigue crack growth in fiber reinforced plastics

Fatigue crack growth in fiber composites occurs by such complex modes as to frustrate efforts at developing comprehensive theories and models. Under certain loading conditions and with certain types of reinforcement, simpler modes of fatigue crack growth are observed. These modes are more amenable to modeling efforts, and the fatigue crack growth rate can be predicted in some cases. Thus, a formula for prediction of ligamented mode fatigue crack growth rate is available.

Mandell, J. F.↗
NASA NTRS2010

Shallow and Deep Latent Heating Modes Over Tropical Oceans Observed with TRMM PR Spectral Latent Heating Data

The global hydrological cycle is central to the Earth's climate system, with rainfall and the physics of its formation acting as the key links in the cycle. Two-thirds of global rainfall occurs in the Tropics. Associated with this rainfall is a vast amount of heat, which is known as latent heat. It arises mainly due to the phase change of water vapor condensing into liquid droplets; three-fourths of the total heat energy available to the Earth's atmosphere comes from tropical rainfall. In addition, fresh water provided by tropical rainfall and its variability exerts a large impact upon the structure and motions of the upper ocean layer. Three-dimensional distributions of latent heating estimated from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR)utilizing the Spectral Latent Heating (SLH) algorithm are analyzed. Mass-weighted and vertically integrated latent heating averaged over the tropical oceans is estimated as approx.72.6 J/s (approx.2.51 mm/day), and that over tropical land is approx.73.7 J/s (approx.2.55 mm/day), for 30degN-30degS. It is shown that non-drizzle precipitation over tropical and subtropical oceans consists of two dominant modes of rainfall systems, deep systems and congestus. A rough estimate of shallow mode contribution against the total heating is about 46.7 % for the average tropical oceans, which is substantially larger than 23.7 % over tropical land. While cumulus congestus heating linearly correlates with the SST, deep mode is dynamically bounded by large-scale subsidence. It is notable that substantial amount of rain, as large as 2.38 mm day-1 in average, is brought from congestus clouds under the large-scale subsiding circulation. It is also notable that even in the region with SST warmer than 28 oC, large-scale subsidence effectively suppresses the deep convection, remaining the heating by congestus clouds. Our results support that the entrainment of mid-to-lower-tropospheric dry air, which accompanies the large-scale subsidence is the major factor suppressing the deep convection. Therefore, representation of the realistic entrainment is very important for proper reproduction of precipitation distribution and resultant large-scale circulation.

Takayabu, Yukari N.↗
DOE OSTI2025

Observation of Persistent Zero Modes and Superconducting Vortex Doublets in UTe 2

Superconducting vortices can reveal electron pairing details and nucleate topologically protected states. Yet, vortices of bulk spin-triplet superconductors have never been visualized at the atomic scale. Recently, UTe 2 has emerged as a prime spin-triplet superconductor, but its superconducting order parameter is elusive, and whether time-reversal symmetry (TRS) is broken remains unsettled. Here, in this work, we visualize vortices on the (011) surface of ultraclean UTe 2 single crystals (T c = 2.1 K) using scanning tunneling microscopy (STM). We introduce $\frac{d^{2}𝐼}{d𝑉^{2}}$ imaging as an effective technique for vortex visualization in superconductors with substantial residual zero-energy density of states (DOS), as in UTe 2 . Anisotropic single-flux-quantum vortices, with coherence lengths of ∼12 nm (4 nm) parallel (perpendicular) to the a -axis, form a triangular vortex lattice (VL) under a small out-of-plane magnetic field. The invariance of vortex structures and VL under changes of field polarity and cooling history strongly supports time-reversal invariant superconductivity under zero field. At vortex cores (VCs), nonsplit, spectrally sharp zero-bias conductance peaks (ZBPs) persist up 8 T that are consistent with symmetry-protected Majorana zero modes (MZMs) in a topological vortex line. Close examination of vortex structures reveals a mirror-asymmetric doublet─one with ZBPs and another with an enhanced apparent gap, possibly originating from a field-induced multicomponent order parameter.

UTe2↗
NASA NTRS1971

The silicon vidicon: Integration, storage and slow scan capability - Experimental observation of a secondary mode of operation.

Description of the performance of the silicon diode array vidicon - an imaging sensor which possesses wide spectral response, high quantum efficiency, and linear response. These characteristics, in addition to its inherent ruggedness, simplicity, and long-term stability and operating life make this device potentially of great usefulness for ground-base and spaceborne planetary and stellar imaging applications. However, integration and charged storage for periods greater than approximately five seconds are not possible at room temperature because of diode saturation from dark current buildup. Since dark current can be reduced by cooling, measurements were made in the range from -65 to 25 C. Results are presented on the extension of integration, storage, and slow scan capabilities achievable by cooling. Integration times in excess of 20 minutes were achieved at the lowest temperatures. The measured results are compared with results obtained with other types of sensors and the advantages of the silicon diode array vidicon for imaging applications are discussed.

Ando, K. J.↗
NASA NTRS1988

Synchronously pumped mode-locked Ti:Al2O3 lasers

Synchronously pumped mode-locked laser operation in a Ti:Al2O3 ring laser is demonstrated. The laser pump source was a frequency-doubled Nd:YAG laser-amplifier system producing a 60-micron-long macropulse that comprised a wavetrain of mode-locked 70-ps micropulses with a 10-ns spacing (100 MHz). The Ti:Al2O3 laser consisted of a 1-cm-long crystal with faces cut at the Brewster angle and placed in a ring laser cavity configuration with a 2 percent output coupling mirror. The cavity was adjusted for a 5-ns round trip transit time, which was close to half the temporal spacing of the pump pulse. When the crystal was pumped synchronously at 532 nm with a 30-mJ macropulse, which was approximately an order of magnitude above the laser threshold, mode-locked lasing at approximately 200 MHz was obtained. This macropulse pump energy corresponds to an average micropulse pump energy of about 5 microJ at the Ti:Al2O3 crystal face. The mode-locked operation of the Ti:Al2O3 was observed only after several microseconds into the macropulse, indicating a long build-up process over many cavity trips. During this time, relaxation oscillations were observed. When mode locking started, the relaxation oscillation frequency increased by an order of magnitude. Synchronous pumping has been limited to operation with dye lasers and used either a CW or pulsed mode-locked pump source. Recent work has demonstrated CW mode-locked operation of a Ti:Al2O3 laser. The result raises the possibility that pulsed synchronous pumping may be used to obtain significantly narrowed laser pulses in Ti:Al2O3.

Source record↗
NASA NTRS1990

Observation of the Z mode with DE 1 and its analysis by three-dimensional ray tracing

Certain Z-mode wave emissions in the earth's magnetosphere have been identified using the wave spectra and polarization measurements of the DE 1 satellite. Although such emissions accompany the aurora, and thus presumably originate from the evening-sector auroral zone, they are found to occur over much wider ranges of latitude and longitude. Since the predicted cyclotron maser emission at the cyclotron frequency could not have produced waves which travel such great distances, as shown by three-dimensional ray tracing, it is proposed instead that these emissions must originate from lower altitudes within the auroral zone and probably from near the plasma frequency inside the auroral plasma cavity.

Hashimoto, Kozo↗
NASA NTRS2007

Convective-Stratiform Precipitation Variability at Seasonal Scale from Eight Years of TRMM Observations: Implications for Multiple Modes of Diurnal Variability

This study investigated the variability of convective and stratiform rainfall from eight years (1998-2005) of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) and TRMM Microwave Imager (TMI) measurements--focusing on seasonal diurnal variability. The main scientific goals are: (1) to understand the climatological variability of these two dominant forms of precipitation across the four cardinal seasons and over continents and oceans separately, and (2) to understand how differences in convective and stratiform rainfall variations ultimately determine how diurnal variability of total rainfall is modulated into multiple modes. There are distinct day-night differences for both convective and stratiform rainfall. Oceanic (continental) convective rainfall is up to 25% (50%) greater during nighttime (daytime) than daytime (nighttime). Seasonal variability of convective rainfall's day-night difference is relatively small, while stratiform rainfall exhibits very apparent day-night variations with a seasonal variability of these variations. There are consistent late evening diurnal peaks without obvious seasonal variations over ocean for convective, stratiform, and total rainfall. Over continents, convective and total rainfall exhibit a consistent dominant afternoon peak with little seasonal variability--with a late evening secondary peal exhibiting seasonal variation. Stratiform rainfall over continents shows a consistent strong late evening peak with a weak afternoon peak--with the afternoon mode undergoing seasonal variability. Therefore, the diurnal characteristics of stratiform rainfall control the afternoon secondary maximum of oceanic rainfall and the late evening secondary peak of continental rainfall. Even at seasonal-regional scale spatially or an interannual global scale temporally, the secondary mode can become very pronounced, but on an intermittent basis. Overall, the results demonstrate the importance of partitioning total rainfall into convective and stratiform components and that diurnal modes largely arise from distinct diurnal stratiform variations modulating convective variations.

Yang, Song↗
NASA NTRS2018

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

The Magnetospheric Multiscale mission has observed electron whistler waves at the center and at the edges of magnetic holes in the dayside magnetosheath. The magnetic holes are nonlinear mirror structures since their magnitude is anticorrelated with particle density. In this article, we examine the growth mechanisms of these whistler waves and their interaction with the host magnetic hole. In the observations, as magnetic holes develop and get deeper, an electron population gets trapped and develops a temperature anisotropy favorable for whistler waves to be generated. In addition, the decrease in magnetic field magnitude and the increase in density reduce the electron resonance energy, which promotes the electron cyclotron resonance. To investigate this process, we used expanding box particle-in-cell simulations to produce the mirror instability, which then evolve into magnetic holes. The simulation shows that whistler waves can be generated at the center and edges of magnetic holes, which reproduces the primary features of the MMS observations. The simulation shows that the electron temperature anisotropy develops in the center of the magnetic hole once the mirror instability reaches its nonlinear stage of evolution. The plasma is then unstable to whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are developed, the electron temperature anisotropy appears at the edges of the holes and electron distributions become more isotropic at the magnetic field minimum. At the edges, the expansion of magnetic holes decelerates the electrons, which leads to temperature anisotropies.

Magnetospheric Multiscale↗
DOE OSTI2025

Fast-ion-driven Alfvén eigenmodes during ICRF-heated high β p plasmas on EAST

Fast-ion-driven Alfvén eigenmodes (AEs) are observed during ICRF-heated high-β p plasmas on EAST. Multiple high frequency modes are observed for shot 112670 at f TAE1 ~ 145 kHz, δB/B ~ 4 × 10 –4 and f TAE2 ~ 175 kHz, δB/B ~ 1.2 × 10 –5 measured by high-frequency Mirnov coils, at B 0 ~ 2.45 T, I p ~ 350kA, n e ramp-up from 3.5 × 10 19 to 4 × 10 19 m −3 at P ECRH ~ 2 MW, PLHW ~ 2 MW, and P ICRH ~ 2.1 MW. Here, 37 MHz ICRF minority hydrogen heating scheme, located at plasma core, creates fast ion population which drives TAEs unstable from TORIC + SFFPQL. In the experiment, it is observed that the evolution of mode frequency depends on electron density, following the theoretical TAE frequency characteristic $f_{{{\text{th}}}} = V_{{\text{a}}} /(4\pi qR) \propto \sqrt {n_{{\text{e}}} }$. As the electron density increases, the amplitude of the AE mode progressively diminishes. Higher plasma density shortens the fast-ion slowing-down time, reduces the heating efficiency of minority hydrogen, weakens the high-energy tail, and consequently decreases the fast-ion beta. Based on the diagnostic results from the microwave reflectometer and electron cyclotron emission (ECE) diagnostics, the TAE is located within the plasma core, consistent with the narrower core region of the TAE gap observed in the continuous spectrum.

Pan, C. Y. [Chinese Academy of Sciences, Hefei (Ch↗
NASA NTRS1990

Resonant absorption of p-modes by sunspots

Explanations for the observed p-mode absorption in sunspots are examined. It is demonstrated that any dissipative process like radiative, viscous, or resistive dissipation leads to the resonant absorption of acoustic waves incident on the sunspot tube, and that the resultant heating rate can be shown to be consistent with the observed absorption of the p-mode power impinging on an isolated inhomogeneously structured sunspot.

Chitre, S. M.↗
NASA NTRS2021

Scheduling and Operations of the Orbiting Carbon Observatory-3 Mission

This paper describes the development and use of an automated scheduling system for the National Aeronautics and Space Administration’s (NASA) Orbiting Carbon Observatory-3 (OCO-3) Mission. OCO-3 measures atmospheric carbon dioxide from space. Made from the spare instrument built as a backup to the Orbiting Carbon Observatory-2 (OCO-2), OCO-3 extends the rich set of data collected by OCO-2. OCO-3 is outfitted with an agile Pointing Mirror Assembly (PMA) that allows for more detailed types of observations and rapid mode transitions. The mission uses an adaptation of the Compressed Large-scale Activity Scheduling and Planning (CLASP) system for scheduling nominal operations, as well as a separate automated scheduling system developed for scheduling observations for the calibration of the PMA. CLASP is used to schedule the four types of observational modes: Nadir, Glint, Target, and Snapshot Area Map. OCO-3 has a variety of complex mission-specific geometric constraints that were incorporated into CLASP to produce schedules that ensure instrument safety.

Moy, Alan↗
NASA NTRS1975

An investigation of the edge-sliding mode in fracture mechanics

A boundary collocation procedure has been applied to the Williams stress function to determine the elastic stress distribution for the crack tip region of a finite, edge-cracked plate subjected to mode II loading at the crack tips. The asymmetric specimen selected was particularly suitable for the determination of plane strain fracture toughness for mode II loading. Numerical solutions for stress intensity factors for the edge-sliding mode obtained by the boundary collocation method were in close agreement with values obtained from photoelastic experiments. Fracture tests of several compact shear specimens of 2024-T4 aluminum were conducted in order to experimentally investigate the behavior of the edge-sliding mode. In each case a brittle shear failure was observed and mode II fracture toughness values were obtained. The average value for K-IIc obtained from two tests was 39.5 ksi radical (in). No K-Ic data for 2024-T4 were available for comparison purposes; however, K-Ic values for a similar alloy, 2024-T351, have been reported as 34 ksi radical (in) which is only about 15 per cent below the corresponding K-IIc value.

Jones, D. L.↗
NASA NTRS2017

Global Observations of Magnetospheric High-m Poloidal Waves During the 22 June 2015 Magnetic Storm

We report global observations of high-m poloidal waves during the recovery phase of the 22 June 2015 magnetic storm from a constellation of widely spaced satellites of five missions including Magnetospheric Multiscale (MMS), Van Allen Probes, Time History of Events and Macroscale Interactions during Substorm (THEMIS), Cluster, and Geostationary Operational Environmental Satellites (GOES). The combined observations demonstrate the global spatial extent of storm time poloidal waves. MMS observations confirm high azimuthal wave numbers (m approximately 100). Mode identification indicates the waves are associated with the second harmonic of field line resonances. The wave frequencies exhibit a decreasing trend as L increases, distinguishing them from the single-frequency global poloidal modes normally observed during quiet times. Detailed examination of the instantaneous frequency reveals discrete spatial structures with step-like frequency changes along L. Each discrete L shell has a steady wave frequency and spans about 1 RE, suggesting that there exist a discrete number of drift-bounce resonance regions across L shells during storm times.

Le, G.↗
NASA NTRS2006

Solving Cassini's Data Glitch Problem during Coherency Mode Transition for Titan Radar Observations

We describe the problem of regular small telemetry losses incurred during coherency mode transitions in Cassini's telecommunication. The project did not originally plan any corrective steps for avoiding these data losses, because of 1) the disparity between the small durations of the transitions (1-2 min) and large playback capability losses (15 min) needed for bracketing the transition time spans and 2) the unpredictable content of data downlinking during the transitions. However, as the intense science data return from the tour began, it became apparent that the impact of these small losses can sometimes be significant. We provide two examples of the impact on Radar-dedicated Titan flybys.

telecommunications↗
NASA NTRS2006

Solving Cassini's data glitch problem during coherency mode transition for Titan radar observations

We describe the problem of regular small telemetry losses incurred during coherency mode transitions in Cassini’s telecommunication. The project did not originally plan any corrective steps for avoiding these data losses, because of 1) the disparity between the small durations of the transitions (1-2 min) and large playback capability losses (15 min) needed for bracketing the transition time spans and 2) the unpredictable content of data downlinking during the transitions. However, as the intense science data return from the tour began, it became apparent that the impact of these small losses can sometimes be significant. We provide two examples of the impact on Radar-dedicated Titan flybys. In general, the impacts are larger for high-rate data and for data acquired during a targeted flyby of Titan and other icy satellites. Although the content of data during a transition for every downlink pass is unpredictable, we are certain that some important data will be lost on downlink passes dedicated to transmit the flyby data and it does not matter what part of the data will be hit by the transitions. We collected more than 200 days of data from Cassini tour operations between June 2004 and February 2005 to analyze the distributions of the start time and duration of the transitions. We found that the occurrence of a transition can be predicted within a 5-min window, with 95 percent confidence. Given that, it is possible to eliminate the data losses by pausing playback at the beginning of a transition for 5 minutes and resuming playback after transition completion. We briefly describe three operational fixes as to how to implement the playback pause, with the pros and cons for each method. Finally, we report the results of the method chosen by the project and implemented on the spacecraft for several Titan and icy satellites flybys between September and October, 2005.

Weld, K. R.↗
NASA NTRS2001

Functionalization of Carbon Nanotubes using Atomic Hydrogen

We have investigated the irradiation of multi walled and single walled carbon nanotubes (SWNTs) with atomic hydrogen. After irradiating the SWNT sample, a band at 2940/cm (3.4 microns) that is characteristic of the C-H stretching mode is observed using Fourier transform infrared (FTIR) spectroscopy. Additional confirmation of SWNT functionalization is tested by irradiating with atomic deuterium. A weak band in the region 1940/cm (5.2 micron) to 2450/cm (4.1 micron) corresponding to C-D stretching mode is also observed in the FTIR spectrum. This technique provides a clean gas phase process for the functionalization of SWNTs, which could lead to further chemical manipulation and/or the tuning of the electronic properties of SWNTs for nanodevice applications.

Khare, Bishun N.↗