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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 1,405 records · Page 78
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Magnetic Flux Emergence and Decay Rates for Preceder and Follower Sunspots Observed with HMI

We quantify the emergence and decay rates of preceder (p) and follower (f) sunspots within 10 active regions from 2010 to 2014 using Space-weather Helioseismic Magnetic Imager Active Region Patch data. The sunspots are small to mid-sized regions and contain a signed flux within a single polarity sunspot of (1.1--6.5)×10{sup 21} Mx. The net unsigned flux within the regions, including plage, ranges from (5.1--20)×10{sup 21} Mx. Rates are calculated with and without intensity contours to differentiate between sunspot formation and flux emergence. Signed flux emergence rates, calculated with intensity contours, for the p (f) spots average 6.8(4.9)×10{sup 19} Mx hr{sup −1}, while decay rates are −1.9(−3.4)×10{sup 19} Mx hr{sup −1}. The mean, signed flux emergence rate of the regions, including plage, is 7.1×10{sup 19} Mx hr{sup −1}, for a mean peak flux of 5.9×10{sup 21} Mx. Using a synthesis of these results and others reported previously, there is a clear trend for larger flux regions to emerge faster than smaller ones. Observed emergence rates (dϕ/dt, Mx hr{sup −1}) scale with total signed peak flux, ϕ-tilde {sub max}, as a power law with an exponent of 0.36, i.e., dϕ/dt=A ϕ-tilde {sub max}{sup 0.36}. The observed rates may assist in constraining the boundary and initial conditions in simulations which already demonstrate increased rates for flux tubes with higher buoyancy and twist, or in the presence of a strong upflow. Overall, the observed emergence rates are smaller than those in simulations, which may indicate a slower rise of the flux in the interior than what is captured in simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

A Comprehensive Review of Latent Space Dynamics Identification Algorithms for Intrusive and Non-Intrusive Reduced-Order-Modeling

Numerical solvers of partial differential equations (PDEs) have been widely employed for simulating physical systems. However, the computational cost remains a major bottleneck in various scientific and engineering applications, which has motivated the development of reduced-order models (ROMs). Recently, machine-learning-based ROMs have gained significant popularity and are promising for addressing some limitations of traditional ROM methods, especially for advection dominated systems. In this chapter, we focus on a particular framework known as Latent Space Dynamics Identification (LaSDI), which transforms the high-fidelity data, governed by a PDE, to simpler and low-dimensional latent-space data, governed by ordinary differential equations (ODEs). These ODEs can be learned and subsequently interpolated to make ROM predictions. Each building block of LaSDI can be easily modulated depending on the application, which makes the LaSDI framework highly flexible. In particular, we present strategies to enforce the laws of thermodynamics into LaSDI models (tLaSDI), enhance robustness in the presence of noise through the weak form (WLaSDI), select high-fidelity training data efficiently through active learning (gLaSDI, GPLaSDI), and quantify the ROM prediction uncertainty through Gaussian processes (GPLaSDI). We demonstrate the performance of different LaSDI approaches on Burgers equation, a non-linear heat conduction problem, and a plasma physics problem, showing that LaSDI algorithms can achieve relative errors of less than a few percent and up to thousands of times speed-ups.

Computational Engineering, Finance, and Science (c↗
DOE OSTI2020

Environmental controls on ecosystem-scale cold-season methane and carbon dioxide fluxes in an Arctic tundra ecosystem

Abstract. Understanding the processes that influence and control carbon cycling in Arctic tundra ecosystems is essential for making accurate predictions about what role these ecosystems will play in potential future climate change scenarios. Particularly, air–surface fluxes of methane and carbon dioxide are of interest as recent observations suggest that the vast stores of soil carbon found in the Arctic tundra are becoming more available to release to the atmosphere in the form of these greenhouse gases. Further, harsh wintertime conditions and complex logistics have limited the number of year-round and cold-season studies and hence too our understanding of carbon cycle processes during these periods. We present here a two-year micrometeorological data set of methane and carbon dioxide fluxes, along with supporting soil pore gas profiles, that provide near-continuous data throughout the active summer and cold winter seasons. Net emission of methane and carbon dioxide in one of the study years totalled 3.7 and 89 g C m−2 a−1 respectively, with cold-season methane emission representing 54 % of the annual total. In the other year, net emission totals of methane and carbon dioxide were 4.9 and 485 g C m−2 a−1 respectively, with cold-season methane emission here representing 82 % of the annual total – a larger proportion than has been previously reported in the Arctic tundra. Regression tree analysis suggests that, due to relatively warmer air temperatures and deeper snow depths, deeper soil horizons – where most microbial methanogenic activity takes place – remained warm enough to maintain efficient methane production whilst surface soil temperatures were simultaneously cold enough to limit microbial methanotrophic activity. These results provide valuable insight into how a changing Arctic climate may impact methane emission, and highlight a need to focus on soil temperatures throughout the entire active soil profile, rather than rely on air temperature as a proxy for modelling temperature–methane flux dynamics.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1973

High efficiency ground data transmission

It is demonstrated that state-of-the-art communications technology can be implemented and reliably operated on a global basis to increase the transmission rates and efficiencies on circuits with bandwidths greater than the typical speech channel. Optimization is affected by optimum clock recovery procedures, multilevel pulse amplitude modulation, single sideband amplitude modulation, transversal filter equalizers, data scrambling, and active compensation for phase instability.

Dickinson, W. B.↗
NASA NTRS1975

Summary of the Active Microwave Workshop, chapter 1

An overview is given of the utility, feasibility, and advantages of active microwave sensors for a broad range of applications, including aerospace. In many instances, the material provides an in-depth examination of the applicability and/or the technology of microwave remote sensing, and considerable documentation is presented in support of these techniques. An assessment of the relative strengths and weaknesses of active microwave sensor data indicates that satisfactory data are obtainable for several significant applications.

Source record↗
NASA NTRS1975

LANDSAT survey of near-shore ice conditions along the Arctic coast of Alaska

The author has identified the following significant results. On the basis of analysis of late winter 1973, 1974, and 1975 LANDSAT imagery of the Beaufort Sea coast of Alaska, the following conclusions regarding near-shore ice conditions were made: (1) by March, the seaward limit of contiguous ice is often beyond the 10 fathom contour. (2) During March, shearing can and does take place along a line roughly coincident with the 10 fathom contour. (3) Ice motions during these shearing events are not extremely great, generally on the order of 10 km. (4) Many large ice features have already been formed by late February. (5) Based on look-ahead at later LANDSAT imagery, it seems apparent that Beaufort Seas shore-fast ice was already formed by late February and may well be safe for exploratory activities from this data forward until the melt season.

Stringer, W. J.↗
NASA NTRS1976

The triggering and subsequent development of a solar flare

A solar flare which occurred on Sept. 5, 1973, is discussed on the basis of high temporal and spatial resolution pictures taken with the Skylab S-056 X-ray telescope. The temporal evolution of the flare is outlined, and magnetic-field data for the active region are compared with the soft X-ray observations. A close similarity between calculated magnetic-field lines and the overall structure of the X-ray core is shown to suggest that the flare occurred in an entire arcade of loops rather than in a single loop. Sequential brightening of different X-ray features is taken as an indication that some triggering disturbance moved from one side to the other in the flare core at velocities of 180 to 280 km/s. The two most intense X-ray features were found in places where the magnetic field composing the arcade had a small radius of curvature with horizontal field gradients higher than the surrounding area and where the axis of the arcade changed direction. It is suggested that a magetosonic wave triggered the energy releases as it propagated down the arcade and steepened the field gradients

Vorpahl, J. A.↗
NASA NTRS1977

The plasmapause revisited

A statistical investigation is conducted concerning the plasmapause behavior observed from Explorer 45 during various levels of magnetic activity. Aspects of data handling are reported and the implications of a constant density level for a plasmapause definition are discussed. The average local time dependence of the gradient saturation events and the sharp saturation events detected on Explorer 45 is shown with the aid of graphs. Other graphs show the results of the statistical processing operations. The significance of the obtained data is discussed.

Maynard, N. C.↗
NASA NTRS1975

Dunite 72417 - A chemical study and interpretation

The rock selected for the study is one of the rare ultrabasic rocks, which seems to have survived early lunar differentiation. The Rb-Sr internal isochron for this dunite gave an age of about 4.55 AE. The dunite was sampled at Apollo 17, Station 2 from a single 10x20-cm clast incorporated into a KREEP-rich blue-gray breccia 72435, Boulder 3. Nine dunite samples were analyzed with the aid of instrumental and radiochemical neutron activation analysis procedures. Data for 27 elements are shown in a table. Attention is given to trapped liquid (magma), a garnet hypothesis, models for the dunite genesis, and magma compositions from which 15415 and 72417 crystallized.

Laul, J. C.↗
NASA NTRS1981

Pilot Fatigue and Circadian Desynchronosis

Pilot fatigue and circadian desynchronosis, its significance to air transport safety, and research approaches, were examined. There is a need for better data on sleep, activity, and other pertinent factors from pilots flying a variety of demanding schedules. Simulation studies of flight crew performance should be utilized to determine the degree of fatigue induced by demanding schedules and to delineate more precisely the factors responsible for performance decrements in flight and to test solutions proposed to resolve problems induced by fatigue and desynchronosis. It was concluded that there is a safety problem of uncertain magnitude due to transmeridian flying and a potential problem due to fatigue associated with various factors found in air transport operations.

Source record↗