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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Evaluating the Bulk Lorentz Factors of Outflow Material: Lessons Learned from the Extremely Energetic Outburst GRB 160625B

GRB 160625B is an extremely bright outburst with well-monitored afterglow emission. The geometry-corrected energy is high, up to ∼5.2 × 10{sup 52} erg or even ∼8 × 10{sup 52} erg, rendering it the most energetic GRB prompt emission recorded so far. We analyzed the time-resolved spectra of the prompt emission and found that in some intervals there were likely thermal-radiation components and the high energy emission was characterized by significant cutoff. The bulk Lorentz factors of the outflow material are estimated accordingly. We found out that the Lorentz factors derived in the thermal-radiation model are consistent with the luminosity-Lorentz factor correlation found in other bursts, as well as in GRB 090902B for the time-resolved thermal-radiation components, while the spectral cutoff model yields much lower Lorentz factors that are in tension with the constraints set by the electron pair Compton scattering process. We then suggest that these spectral cutoffs are more likely related to the particle acceleration process and that one should be careful in estimating the Lorentz factors if the spectrum cuts at a rather low energy (e.g., ∼tens of MeV). The nature of the central engine has also been discussed, and a stellar-mass black hole is favored.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Lanthanides or Dust in Kilonovae: Lessons Learned from GW170817

The unprecedented optical and near-infrared lightcurves of the first electromagnetic counterpart to a gravitational-wave source, GW170817, a binary neutron star merger, exhibited a strong evolution from blue to near-infrared (a so-called “kilonova” or “macronova”). The emerging near-infrared component is widely attributed to the formation of r-process elements that provide the opacity to shift the blue light into the near-infrared. An alternative scenario is that the light from the blue component gets extinguished by dust formed by the kilonova and subsequently is re-emitted at near-infrared wavelengths. We test here this hypothesis using the lightcurves of AT 2017gfo, the kilonova accompanying GW170817. We find that of the order of 10{sup −5} M{sub ⊙} of carbon is required to reproduce the optical/near-infrared lightcurves as the kilonova fades. This putative dust cools from ∼2000 K at ∼4 days after the event to ∼1500 K over the course of the following week, thus requiring dust with a high condensation temperature, such as carbon. We contrast this with the nucleosynthetic yields predicted by a range of kilonova wind models. These suggest that at most 10{sup −9} M{sub ⊙} of carbon is formed. Moreover, the decay in the inferred dust temperature is slower than that expected in kilonova models. We therefore conclude that in current models of the blue component of the kilonova, the near-infrared component in the kilonova accompanying GW170817 is unlikely to be due to dust.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Moving beyond post hoc explainable artificial intelligence: a perspective paper on lessons learned from dynamical climate modeling

AI models are criticized as being black boxes, potentially subjecting climate science to greater uncertainty. Explainable artificial intelligence (XAI) has been proposed to probe AI models and increase trust. In this review and perspective paper, we suggest that, in addition to using XAI methods, AI researchers in climate science can learn from past successes in the development of physics-based dynamical climate models. Dynamical models are complex but have gained trust because their successes and failures can sometimes be attributed to specific components or sub-models, such as when model bias is explained by pointing to a particular parameterization. We propose three types of understanding as a basis to evaluate trust in dynamical and AI models alike: (1) instrumental understanding, which is obtained when a model has passed a functional test; (2) statistical understanding, obtained when researchers can make sense of the modeling results using statistical techniques to identify input–output relationships; and (3) component-level understanding, which refers to modelers' ability to point to specific model components or parts in the model architecture as the culprit for erratic model behaviors or as the crucial reason why the model functions well. We demonstrate how component-level understanding has been sought and achieved via climate model intercomparison projects over the past several decades. Such component-level understanding routinely leads to model improvements and may also serve as a template for thinking about AI-driven climate science. Currently, XAI methods can help explain the behaviors of AI models by focusing on the mapping between input and output, thereby increasing the statistical understanding of AI models. Yet, to further increase our understanding of AI models, we will have to build AI models that have interpretable components amenable to component-level understanding. We give recent examples from the AI climate science literature to highlight some recent, albeit limited, successes in achieving component-level understanding and thereby explaining model behavior. The merit of such interpretable AI models is that they serve as a stronger basis for trust in climate modeling and, by extension, downstream uses of climate model data.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Observations and Lessons Learned in Residential Roofing Integrated Photovoltaics

The data file includes field observations of residential roofing integrated photovoltaics installation that happened between July 2021 and June 2022 in California. There are 21 observations - 2 in the re-roofing category and 19 in the new construction category. The file includes two time and motion forms (Re-Roofing & New Construction) we used to capture the time it takes for each activity in the rooftop solar and electrical installation process. You will see the duration for detailed steps along with activities that are included for total installation time for the paper. There are three parts to the time and motion form - Part 1 has project and crew characteristics, product information, and inspection and permitting data and can be filled before the installation. Part 2 has the actual installation time stamps and related notes. Part 3 has the crew information and can be filled on-site or off-site, but this section is optional. The re-roofing form has pre-solar activities and gutters and vents section in Part 2 of the form, whereas new construction form includes a section for capturing the time it took for rough wiring. The re-roofing form does not include rough wiring but instead includes the final electrical wiring process. These are the key differences in both the forms. Each day/step/installation activity needs to include the crew break time as they happen and there is space available to capture the crew breaks duration. In Table 1 below, the different terms used in the time and motion form are defined and their corresponding unit of measurement stated. We also highlight the optional sections. The data is captured in total mins, total hours, person mins, person hours. You can use this form or make edits to the form to recreate the study or make your own observations. The data herein was reviewed but may not be comprehensive. NREL invites questions and inputs to improve the data, including to: Correct erroneous information Fill in missing/updated information Clarifications on data and variables Updated information may be submitted to Sushmita Jena at sushmita.jena@nlr.gov.

14 SOLAR ENERGY↗
NASA NTRS1971

Lessons learned from a decade of international space cooperation.

A case history of the Alouette/ISIS series is presented, giving attention to aspects of U.S.-Canadian cooperation in this program. The project is only one example of a broad network of international cooperative relationships established by NASA over the past decade. Participation by other countries in important space science and applications projects is not limited to those providing flight hardware or conducting flight observations. Much valuable work is done on the ground, ranging from analysis in the laboratories of samples returned from the moon to correlated ground-based reception and analysis of radio beacon signals from satellites. It was found that cooperation is more likely to proceed smoothly and produce beneficial results if it is focused on projects that are clearly defined and agreed on in advance.

Barnes, R. J. H.↗
NASA NTRS1980

Mission management - Lessons learned from early Spacelab missions

The concept and the responsibilities of a mission manager approach are reviewed, and some of the associated problems in implementing Spacelab mission are discussed. Consideration is given to program control, science management, integrated payload mission planning, and integration requirements. Payload specialist training, payload and launch site integration, payload flight/mission operations, and postmission activities are outlined.

Craft, H. G., Jr.↗
NASA NTRS1980

Differentiation of crusts and cores of the terrestrial planets - Lessons for the early earth

The extent and mechanisms of global differentiation and the early thermal and tectonic histories of the terrestrial planets are surveyed in order to provide constraints on the first billion years of earth history. Indirect and direct seismic evidence for crusts on the moon, Mars and Venus is presented, and it is pointed out that substantial portions of these crusts have been in place since the cessation of heavy bombardment of the inner solar system four billion years ago. Evidence for sizable cores on Mars and Mercury and a small core on the moon is also discussed, and the heat involved in core formation is pointed out. Examination of the volcanic and tectonic histories of planets lacking plate tectonics indicates that core formation was not closely linked to crust formation on the moon or Mars, with chemical differentiation restricted to shallow regions, and was much more extensive on Mercury. Extension of these considerations to the earth results in a model of a hot and vigorously convecting mantle with an easily deformable crust immediately following core formation, and the gradual development of a lithosphere and plates.

Solomon, S. C.↗
NASA NTRS1981

The OSS-1 mission - Lessons learned in developing and integrating experiments

Experience gained in the development and integration of experiments for the OSS-1 payload to be carried on board the Space Shuttle for the characterization of the effects of the STS environment on future scientific missions is related. Following a review of mission objectives, including the demonstration of Shuttle research capabilities and the evaluation of new technology, the experiments and mission operations to be performed are outlined, and mission support requirements are indicated. The conduct of mission management by the Goddard Space Flight Center, which required interfacing with a large number of other agencies, centers, and investigators and contractors and an enormous amount of formal documentation, is then examined, with consideration given to the management of mechanical, electrical, and thermal systems development mock-up construction, EMI/EMC and acoustic testing, the formation of an integration and test team, and trade-offs between cost, schedule and performance. It is concluded that although work still remains to be done, significant progress has been made in ensuring that the STS is a viable system for space exploration.

Kissin, K.↗