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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Comparison of Columnar Water-Vapor Measurements from Solar Transmittance Methods

The Atmospheric Radiation Measurement program studied water vapor abundance measurement at its southern Great Plains site in the fall of 1997. The program used a large number of instruments, including four solar radiometers. By measuring solar transmittance in the 0.94 micrometer water apor absorption band, they were able to measure columnar water vapor (CWV). In the second round of comparison we used the same radiative transfer model, and the same line-by-line code (which includes recently corrected H2O spectroscopy) to retrieve CWV from all four solar radiometers, thus decreasing the mean CWV by 8 - 13 %. The model was not responsible for the 8 % spread in CWV which remained.

Schmid, Beat↗
NASA NTRS2003

Mesospheric Non-Migrating Tides Generated With Planetary Waves: II Influence of Gravity Waves

We demonstrated that, in our model, non-linear interactions between planetary waves (PW) and migrating tides could generate in the upper mesosphere non-migrating tides with amplitudes comparable to those observed. The Numerical Spectral Model (NSM) we employ incorporates Hines Doppler Spread Parameterization for small-scale gravity waves (GW), which affect in numerous ways the dynamics of the mesosphere. The latitudinal (seasonal) reversals in the temperature and zonal circulation, which are largely caused by GWs (Lindzen, 198l), filter the PWs and contribute to the instabilities that generate the PWs. The PWs in turn are amplified by the momentum deposition of upward propagating GWs, as are the migrating tides. The GWs thus affect significantly the migrating tides and PWs, the building blocks of non-migrating tides. In the present paper, we demonstrate that GW filtering also contributes to the non-linear coupling between PWs and tides. Two computer experiments are presented to make this point. In one, we simply turn off the GW source to show the effect. In the second case, we demonstrate the effect by selectively suppressing the momentum source for the m = 0 non-migrating tides.

Mayr, H. G.↗
NASA NTRS2003

Ambient and Cryogenic Alignment Verification and Performance of the Infrared Multi-Object Spectrometer

The Infrared Multi-Object Spectrometer (IRMOS) is a facility instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 micron) spectrometer with low- to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arc-min field of view using a commercial Micro Electro-Mechanical Systems (MEMS) Digital Micro-mirror Device (DMD) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the DMD field stop, and the spectrograph images the DMD onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and the ambient and cryogenic imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve to venfy alignment, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides further verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides spectral lines at 546.1 nm and 1550 nm, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard test results validate this prediction. We conclude with an instrument performance prediction for first light.

Connelly, Joseph A.↗
NASA NTRS2004

Alignment and Performance of the Infrared Multi-Object Spectrometer

The Infrared Multi-Object Spectrometer (IRMOS) is a principle investigator class instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 micron) spectrometer with low-to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arc-min field of view (4 m telescope) using a commercial Micro Electro-Mechanical Systems (MEMS) micro-mirror array (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and ambient imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve as a qualitative alignment guide, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides a spectral line at 546.1 nanometers, a blackbody source provides a line at 1550 nanometers, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard and instrument level test results validate this prediction. We conclude with an instrument performance prediction for cryogenic operation and first light in late 2003.

Connelly, Joseph A.↗
NASA NTRS2005

Characterization of colloid thruster beams

In this article we use retarding potential, time of flight, and a Faraday cup, to measure the energy and specific charge distributions of the electrospray particles as a function of the position within the beam, as well as beam profiles. This information is then used, together with a model of the beam, to calculate its spreading.

electric propulsion↗
NASA NTRS2006

The Long-Term Performance of Small-Cell Batteries Without Cell-Balancing Electronics

Tests approx.8 yrs ago showed Sony HC do not imbalance. AEA developed a theory (ESPC 2002): a) Self-discharge (SD) decreases with state-of-charge (SOC); b) Cells diverge to a state of dynamic equilibrium; c) Equilibrium spread depends on cell SD uniformity. Balancing model verified against test data. Short-term measures of SD difficult in Sony cells and very small values, depends on technique. Long-term evidence supports lower SD at low SD. Battery testing best proof of performance, typically mission specific tests.

Pearson, C.↗
NASA NTRS2007

Understanding Neutron Stars using Thermonuclear X-ray Bursts

Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star = EOS model of high density cold matter in the neutron star cores. Extensive observation and analysis of the data from the rising portions of the bursts = modeling of burst oscillations and thermonuclear flame spreading. Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

Bhattacharyya, S.↗
NASA NTRS2007

Neutron Stars and Thermonuclear X-ray Bursts

Studies of thermonuclear X-ray bursts can be very useful to constrain the spin rate, mass and radius of a neutron star approaching EOS model of high density cold matter in the neutron star cores. +k Extensive observation and analysis of the data from the rising portions of the bursts - modeling of burst oscillations and thermonuclear flame spreading. +k Theoretical study of thermonuclear flame spreading on the rapidly spinning neutron stars should be done considering all the main physical effects (including magnetic field, nuclear energy generation, Coriolis effect, strong gravity, etc.).

Bhattacharyya, Sudip↗
NASA NTRS2011

The Increasing Use of Remote Sensing Data in Studying the Climatological Impacts on Public Health

One of the more fortunate outcomes of the capture and transformation of remote sensing data into applied information is their usefulness and impacts to better understanding climatological impacts on public health. Today, with petabytes of remote sensing data providing global coverage of climatological parameters, public health research and policy decision makers have an unprecedented (and growing) data record that relates the effects of climatic parameters, such as rainfall, heat, soil moisture, etc. to incidences and spread of disease, as well as predictive modeling. In addition, tools and services that specifically serve public health researchers and respondents have grown in response to needs of the these information users.

Kempler, Steven↗
NASA NTRS2013

New Stratospheric Dust Belt Due to the Chelyabinsk Bolide

The Ozone Mapping Profiler Suite (OMPS) Limb Profiler (LP) on the recently launched NASA/NOAA NPP/ Suomi satellite detected aerosol excess in the midstratosphere (25-45 km altitude) between 50degN and 70degN latitudes. OMPS/LP observations trace this aerosol plume to the meteor that struck near Chelyabinsk, Russia on 15 February 2013. This new dust layer, located above the Junge aerosol layer, has persisted over at least a 3 month period. Material collected on the ground following the bolide explosion showed that the meteor was mostly composed of olivine and pyroxenes. Simulations using Lagrangian and Eulerian atmospheric models trace the plume back to Chelyabinsk and confirm that the plume altitude was at altitudes between 25 and 45 km. The models also confirm the plume circumpolar longitudinal spreading observed by OMPS/LP, with propagation speeds up to 85 m/s.

Stratospheric aerosol↗
NASA NTRS2023

Estimating the Subsolar Magnetopause Position from Soft X-Ray Images Using a Low-Pass Image Filter

The Lunar Environment heliospheric X-ray Imager (LEXI) and Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) missions will image the Earth’s dayside magnetopause and cusps in soft X-rays after their respective launches in the near future, to specify global magnetic reconnection modes for varying solar wind conditions. To support the success of these scientific missions, it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images. In this research, we introduce a new geometric equation that calculates the subsolar magnetopause position ( R s ) from a satellite position, the look direction of the instrument, and the angle at which the X-ray emission is maximized. Two assumptions are used in this method: (1) The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause, and (2) the magnetopause surface near the subsolar point is almost spherical and thus R s is nearly equal to the radius of the magnetopause curvature. We create synthetic soft X-ray images by using the Open Geospace General Circulation Model (OpenGGCM) global magnetohydrodynamic model, the galactic background, the instrument point spread function, and Poisson noise. We then apply the fast Fourier transform and Gaussian low-pass filters to the synthetic images to remove noise and obtain accurate look angles for the soft X-ray peaks. From the filtered images, we calculate R 2 and its accuracy for different LEXI locations, look directions, and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth. Our method estimates R s with an accuracy of <0.3 R E when the solar wind density exceeds >10 cm -3 . The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields. The method captures the magnetopause motion during southward interplanetary magnetic field turnings. Consequently, the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind conditions. This technique will support the LEXI and SMILE missions in achieving their scientific objectives.

Hyangpyo Kim↗
NASA NTRS1990

A reexamination of the spreading center hypothesis for Ovda and Thetis regiones, Venus

Crumpler et al. (1987) proposed that Ovda and Thetis Regiones are spreading centers. The strong positive correlation between geoid and topography observed in ovda and Thetis is unlike that observed for terrestrial spreading centers. The maximum elevation expected for spreading centers on Venus is 1.5 km, and a cooling plate thermal model predicts a maximum geoid anomaly of 8 m, both much less than observed. Even if a spreading center is operative in Ovda and Thetis, most of the geoid and topography must be due to other mechanisms. Crumplet et al. also proposed the existence of 'cross-strike discontinuities', interpreted as transform fault zones, but the evidence for these structures is not conclusive.

Kiefer, Walter S.↗
NASA NTRS1999

Flame Spread Across Liquids: Experimental Results

The goal of our research on flame spread across a pool of liquid fuel is the quantitative identification of the mechanisms that control the rate and nature of flame spread when the initial temperature of the liquid pool is below the fuel's flash point temperature. Besides numerous experiments in drop towers and 1 g laboratories, we have flown five microgravity (mu-g) experiments on sounding rockets. As described in earlier papers, the first three flights examined the effect of forced opposed airflow over a 2.5 cm deep x 2 cm wide x 30 cm long pool of 1-butanol in mu-g. It was found that the flame spread is much slower and steadier than in 1 g where flame spread has a pulsating character. It was speculated that the flame spread in mu-g resembled the character of pseudo-uniform spread in 1 g; Ito et al later confirmed this conclusively in 1 g experiments. Much of the mu-g flame is also farther from the surface, dimmer, and with less soot, when compared to the 1 g flame. Three-dimensional liquid-phase flow patterns that control the liquid preheating were discovered in both 1 g and mu-g. Our numerical model, restricted to two dimensions, had predicted faster, pulsating flame spread in mu-g for opposed airflow. In examining the differences in the dimensionality of the model and experiment, it was noted that the experiment allowed gas expansion in the lateral direction (across the width of the pool), for which the model could not account. Such lateral expansion could reduce the expansion in the forward and upward directions. Because only these latter directions could be modeled, it was decided to artificially reduce the gas thermal expansion in the predictions. When this was done, satisfactory agreement could be obtained between the predicted and observed spread rates and the steadiness of the spread in microgravity. In 1 g, however, the predicted flame spread character also changed to pseudo-uniform, which disagreed with our 1 g experiments where the spread is pulsating. It was then speculated that gas-phase buoyant flow might oppose the lateral gas expansion, so that the 1 g experiments retained their pulsating flame spread character. If this speculation was valid, a difference in lateral gas expansion should be observable when comparing 1 g and mu-g experiments. Specifically, it was anticipated that greater flow divergence caused by lateral expansion would be measured in mu-g in the absence of a buoyant flow directed towards the flame.

Ross, H. D.↗
NASA NTRS2006

A non-PRE double-peaked burst with oscillations: burning front propagation and stalling

Non-photospheric-radius-expansion (non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames from a rotational pole on the neutron star surface, as we argued in a previous study. Here we analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of such a burst from the low mass X-ray binary (LMXB) system 4U 1636-536, and show that our model (with ignition at high latitudes) can qualitatively explain the observed burst profile, and spectral evolution. Moreover, the evolution of the source radius inferred from the data shows a strong signature of temporary stalling of the burning front, which is an essential ingredient of our model. This implies that an understanding of thermonuclear flame spreading on neutron stars can be achieved by a simultaneous study of the evolution of intensity and spectrum of these bursts. We also report the discovery of millisecond period brightness oscillations from this burst, which is the first such observation from a non-PRE double-peaked burst. Our model can explain the corresponding oscillation amplitude during the first (weaker) peak, and the absence of oscillations during the second peak. We discuss how observations of oscillations during non-PRE double-peaked bursts provide an additional t 001 for understanding thermonuclear flame spreading successfully.

Bhattacharyya, Sudip↗
NASA NTRS2021

TLife-LSTM: Forecasting Future COVID-19 Progression with Topological Signatures of Atmospheric Conditions

Understanding the impact of atmospheric conditions on SARS-CoV2 is critical to model COVID-19 dynamics and sheds a light on the future spread around the world. Furthermore, geographic distri- butions of expected clinical severity of COVID-19 may be closely linked to prior history of respiratory diseases and changes in humidity, tem- perature, and air quality. In this context, we postulate that by tracking topological features of atmospheric conditions over time, we can provide a quanti?able structural distribution of atmospheric changes that are likely to be related to COVID-19 dynamics. As such, we apply the machinery of persistence homology on time series of graphs to extract topological signatures and to follow geographical changes in relative humidity and temperature. We develop an integrative machine learning framework named Topological Lifespan LSTM (TLife-LSTM) and test its predictive capabilities on forecasting the dynamics of SARS-CoV2 cases. We validate our framework using the number of con?rmed cases and hospitalization rates recorded in the states of Washington and California in the USA. Our results demonstrate the predictive potential of TLife-LSTM in forecasting the dynamics of COVID-19 and modeling its complex spatio-temporal spread dynamics.

Gel, Yulia R.↗
NASA NTRS1999

Reflight of the Solid Surface Combustion Experiment: Flame Radiation Near Extinction

In flame spreading in quiescent and low-velocity opposing flows, effects of surface reradiation and flame radiation are important in establishing the spread rate and whether the flame, once ignited, survives to steady spread or extinguishes after a time long compared to the ignition event. A reflight of the Solid Surface Combustion Experiment (SSCE), supported by modelling, demonstrates that for thick, flat fuels, the ultimate fate of the flame is extinction rather than steady spread. A mismatch between the thermal scale in the gas, driven by radiation, and the species diffusion scale, driven by mass diffusion, develops such that the high temperature regions of the flame are ultimately located in a region to which oxygen cannot be supplied at a sufficient rate to sustain reaction, and extinction occurs. Results of the experiment conducted on Space Shuttle mission STS 85 on 9 August 1997 are reviewed. For the flat surface geometry, while the hydrodynamic phenomena associated with opposed-flow flame spread may be treated two dimensionally, the radiative effects are three dimensional, and so modelling the radiative processes, with the mismatch in dimensionality, is difficult. The cylindrical geometry at least one long compared to the radius, provides a configuration in which the radiative processes for spread in the axial direction are two dimensional, thus simplifying the modelling. The cylindrical geometry allows for the development of more sophisticated radiative models without the complication of dimensionality concerns, e.g., discrete transfer, which is discussed in detail by Bundy (1998). Additionally, the cylindrical geometry results in a "focussing" of the heat transfer to the surface and may allow for steady spread for radii that for thick fuels of the same half-thickness there is no steady spread.

Altenkirch, R. A.↗
NASA NTRS1995

Spread Across Liquids: The World's First Microgravity Combustion Experiment on a Sounding Rocket

The Spread Across Liquids (SAL) experiment characterizes how flames spread over liquid pools in a low-gravity environment in comparison to test data at Earth's gravity and with numerical models. The modeling and experimental data provide a more complete understanding of flame spread, an area of textbook interest, and add to our knowledge about on-orbit and Earthbound fire behavior and fire hazards. The experiment was performed on a sounding rocket to obtain the necessary microgravity period. Such crewless sounding rockets provide a comparatively inexpensive means to fly very complex, and potentially hazardous, experiments and perform reflights at a very low additional cost. SAL was the first sounding-rocket-based, microgravity combustion experiment in the world. It was expected that gravity would affect ignition susceptibility and flame spread through buoyant convection in both the liquid pool and the gas above the pool. Prior to these sounding rocket tests, however, it was not clear whether the fuel would ignite readily and whether a flame would be sustained in microgravity. It also was not clear whether the flame spread rate would be faster or slower than in Earth's gravity.

Source record↗
NASA NTRS1993

Opposed-Flow Flame Spreading in Reduced Gravity

Experimental results obtained in drop towers and in Space Shuttle based experiments coupled with modelling efforts are beginning to provide information that is allowing an understanding to be developed of the physics of opposed-flow flame spread at reduced gravity where the spread rate and flow velocity are comparable and of the role played by radiative and diffusive processes in flame spreading in microgravity. Here we describe one Space Shuttle based experiment on flame spreading in a quiescent environment, the Solid Surface Combustion Experiment, SSCE, one planned microgravity experiment on flame spreading in a radiatively-controlled, forced opposing flow environment, the Diffusive and Radiative Transport in Fires Experiment, DARTFire, modelling efforts to support these experiments, and some results obtained to date.

Altenkirch, Robert A.↗