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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 703 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

The DESI DR1 peculiar velocity survey: growth rate measurements from the maximum likelihood fields method

We present the constraint on the growth rate of structure from the combination of DESI DR1 BGS sample, Fundamental Plane, and Tully-Fisher peculiar velocity catalogues using the maximum likelihood fields method. The combined catalogue contains 415,523 galaxy redshifts and 76,616 peculiar velocity measurements. To handle the large amount of data in the DESI DR1 peculiar velocity catalogue, we significantly improve the computational efficiency by rewriting the algorithm with JAX. After removing outliers and Tully-Fisher galaxies that are affected by systematics, we find fσ 8 = 0.483 -0.043 +0.080 (stat) ± 0.018(sys), consistent within 1σ with the power spectrum and correlation function analysis using the same dataset. Combining all three measurements with appropriate correlations, the consensus measurement is fσ 8 (z eff = 0.07) = 0.450±0.055, consistent with Planck +ΛCDM cosmology (fσ 8 = 0.449±0.008). Combining with the high redshift growth rate of structure measurements from DESI ShapeFit, the constraint on the growth index is γ = 0.58±0.11, consistent with GR.

cosmic flows↗
DOE OSTI2022

Implementation and optimization of the PTOLEMY transverse drift electromagnetic filter

The PTOLEMY transverse drift filter is a new concept to enable precision analysis of the energy spectrum of electrons near the tritium β-decay endpoint. Here, we detail the implementation and optimization methods for successful operation of the filter for electrons with a known pitch angle. We present the first demonstrator that produces the required magnetic field properties with an iron return-flux magnet. Two methods for the setting of filter electrode voltages are detailed. The challenges of low-energy electron transport in cases of low field are discussed, such as the growth of the cyclotron radius with decreasing magnetic field, which puts a ceiling on filter performance relative to fixed filter dimensions. Additionally, low pitch angle trajectories are dominated by motion parallel to the magnetic field lines and introduce non-adiabatic conditions and curvature drift. To minimize these effects and maximize electron acceptance into the filter, we present a three-potential-well design to simultaneously drain the parallel and transverse kinetic energies throughout the length of the filter. These optimizations are shown, in simulation, to achieve low-energy electron transport from a 1 T iron core (or 3 T superconducting) starting field with initial kinetic energy of 18.6 keV drained to < 10 eV (< 1 eV) in about 80 cm. This result for low field operation paves the way for the first demonstrator of the PTOLEMY spectrometer for measurement of electrons near the tritium endpoint to be constructed at the Gran Sasso National Laboratory (LNGS) in Italy.

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Grid Integration of Renewable Energy and Energy Storage

Grid integration of renewable energy and energy storage requires forward-looking planning process, and increased emphasizes on reliability, resilience, and equity. Power-electronics based energy generation including solar, wind, distributed energy resources (DERs), and various types of grid-tied energy storage and emerging loads, are reshaping grid operator's understanding on interconnection level performance and responses. This paper will present the ongoing work at PNNL related to power electronics R&D, energy modeling and analysis, and a wide spectrum of grid stability studies and technologies in support of grid integration of renewable energy and energy storage.

Power Electronics, grid integration of renewable e↗
DOE OSTI2020

Xylella fastidiosa causes transcriptional shifts that precede tylose formation and starch depletion in xylem

Abstract Pierce's disease (PD) in grapevine ( Vitis vinifera ) is caused by the bacterial pathogen Xylella fastidiosa . X. fastidiosa is limited to the xylem tissue and following infection induces extensive plant‐derived xylem blockages, primarily in the form of tyloses. Tylose‐mediated vessel occlusions are a hallmark of PD, particularly in susceptible V. vinifera . We temporally monitored tylose development over the course of the disease to link symptom severity to the level of tylose occlusion and the presence/absence of the bacterial pathogen at fine‐scale resolution. The majority of vessels containing tyloses were devoid of bacterial cells, indicating that direct, localized perception of X. fastidiosa was not a primary cause of tylose formation. In addition, we used X‐ray computed microtomography and machine‐learning to determine that X. fastidiosa induces significant starch depletion in xylem ray parenchyma cells. This suggests that a signalling mechanism emanating from the vessels colonized by bacteria enables a systemic response to X. fastidiosa infection. To understand the transcriptional changes underlying these phenotypes, we integrated global transcriptomics into the phenotypes we tracked over the disease spectrum. Differential gene expression analysis revealed that considerable transcriptomic reprogramming occurred during early PD before symptom appearance. Specifically, we determined that many genes associated with tylose formation (ethylene signalling and cell wall biogenesis) and drought stress were up‐regulated during both Phase I and Phase II of PD. On the contrary, several genes related to photosynthesis and carbon fixation were down‐regulated during both phases. These responses correlate with significant starch depletion observed in ray cells and tylose synthesis in vessels.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

The Average Spectrum Norm and Near-Optimal Tensor Completion

We propose the average spectrum norm to study the minimum number of measurements required to approximate a multidimensional array (i.e., sample complexity) via low-rank tensor recovery. Our focus is on the tensor completion problem, where the aim is to estimate a multiway array using a subset of tensor entries corrupted by noise. Our average spectrum norm-based analysis provides near-optimal sample complexities, exhibiting dependence on the ambient dimensions and rank that do not suffer from exponential scaling as the order increases.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2021

Ultracool Dwarfs Observed with the Spitzer Infrared Spectrograph. I. An Accurate Look at the L-to-T Transition at ~300 Myr from Optical Through Mid-infrared Spectrophotometry

Here we present Spitzer IRS 5–14 μm spectra and 16 μm and 22 μm photometry of the T2.5 companion to the ~300 Myr old G0V star HN Peg. We incorporate previous 0.8–5 μm observations to obtain the most comprehensive spectral energy distribution (SED) of an intermediate-gravity L/T-transition dwarf that, together with an accurate Gaia EDR3 parallax of the primary, enables us to derive precise fundamental parameters. We find that young (≈0.1–0.3 Gyr) early-T dwarfs on average have ≈140 K lower effective temperatures, ≈20% larger radii, and similar bolometric luminosities compared to ≳1 Gyr old field dwarfs with similar spectral types. Our accurate infrared spectrophotometry offers new detail at wavelengths where the dominant carbon-bearing molecules have their strongest transitions: at 3.4 μm for methane and at 4.6 μm for carbon monoxide. We assess the performance of various widely available photospheric models and find that models with condensates and/or clouds better reproduce the full SED of this moderately young early-T dwarf. However, cloud-free models incorporating a more general convective instability treatment reproduce at least the low-resolution near-infrared spectrum similarly well. Our analysis of R ≈ 2300 J-band spectra shows that the near-infrared potassium absorption lines in HN Peg B have similar strengths to those seen in both younger and older T2–T3 dwarfs. We conclude that while alkali lines are well established as surface gravity indicators for L-type or warmer stars, they are insensitive to surface gravity in early-T dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Multimodality in the Search for New Physics in Pulsar Timing Data and the Case of Kination-amplified Gravitational-wave Background from Inflation

We investigate the kination-amplified inflationary gravitational-wave background (GWB) interpretation of the signal recently reported by various pulsar timing array (PTA) experiments. Kination is a post-inflationary phase in the expansion history dominated by the kinetic energy of some scalar field, characterized by a stiff equation of state w = 1. Within the inflationary GWB model, we identify two modes that can fit the current data sets (NANOGrav and EPTA) with equal likelihood: the kination-amplification (KA) mode and the ordinary, no-kination-amplification (no-KA) mode. The multimodality of the likelihood motivates a Bayesian analysis with nested sampling. We analyze the free spectra of current PTA data and mock free spectra constructed with higher signal-to-noise ratios using nested sampling. The analysis of the mock spectrum designed to be consistent with the best fit to the NANOGrav 15 yr (NG15) data successfully reveals the expected bimodal posterior for the first time while excluding the reheating mode that appears in the fit to the current NG15 data, making a case for our correct and comprehensive treatment of potential multimodal posteriors arising from future PTA data sets. The resultant Bayes factor is $\mathcal{B}$ $\equiv$ Z no–KA /Z KA = 2.9 ± 1.9, indicating comparable statistical significance between the two modes. Given the theoretical model-building challenges of producing highly blue-tilted primordial tensor spectra, the KA mode has the advantage of requiring less blue primordial spectra, compared with the no-KA mode. The synergy between future cosmic microwave background polarization, pulsar timing, and laser interferometer measurements of gravitational waves will help resolve the ambiguity implied by the multimodal posterior in PTA-only searches.

Cosmology↗
NASA NTRS1971

Operating frequencies for educational satellite services

The factors affecting the choice of transmission frequencies are identified. These include international radio regulations, natural environment, man-made environment, hardware considerations, and interconnection and spectrum space considerations. An analysis is presented of international radio regulations with emphasis on 1963 EARC and 1971 WARC frequency allocations, powerflux density restrictions, and resolutions concerning introduction of broadcasting-satellite systems. Natural-environmental effects were divided into two categories: (1) those due to transionospheric propagation, and (2) those that can be credited to the earth's atmosphere and its constituents. The frequency dependence of the signal attenuation, signal distortion, and contributions to system noise temperature due to environmental effects are discussed, and comparisons were made for frequencies of interest. Man-made environmental effects were examined in terms of various sharing limitations as well as the indigenous noise contribution to the overall system noise.

Singh, J. P.↗
NASA NTRS1969

Laser radar measurements of the aerosol content of the atmosphere

A summary of the results of laser radar observations of atmospheric aerosols is presented along with a description of the laser radar system devised during the study and of the data handling techniques utilized for the analysis of the data of the temporal and spatial distribution of atmospheric aerosols. Current research conducted by the group is directed toward the analysis of the frequency spectrum of laser radar echoes to obtain absolute measurements of the dust content of the atmosphere by resolving the molecular and aerosol contributions to the laser radar echoes.

Grams, G. W.↗