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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Large-scale white noise and cosmology

The generation of white noise on large scales is a generic property of the dynamics of physical systems described by local nonlinear partial differential equations. Nonlinearities prevent the small-scale dynamics from being erased by smoothing. Unresolved small-scale dynamics act as an uncorrelated (white or Poissonian) noise (seemingly stochastic but actually deterministic) contribution to large-scale dynamics. This white noise exists even when the dynamics is very nearly linear. In cases where the power spectrum is sub-Poissonian on large scales, this noise will dominate on the largest scale power no matter the amplitude of the inhomogeneities. Such is the case in the standard model of cosmology, where the primordial density power spectrum is expected to have an almost Harrison-Zel’dovich, P [ k ] ∼ k , spectrum on a much broader range of scales than can be observed. Even though linear gravitational evolution dominates nonlinear corrections by a factor of ∼ 10 5 , the nonobservation of white noise on the Hubble scale precludes the extrapolation of this power law below the comoving 1 pc scale. More generally, observation or nonobservation of large-scale white noise provides a powerful probe of the Universe on very small scales in the early Universe. Gravitational radiation, phase transitions, vorticity, and running of the spectral index are all phenomena that can be probed with large-scale white noise. Large-scale white noise is a nonoptional feature of all cosmological models but one which has not heretofore been appreciated.

Barenboim, Gabriela [Valencia U., IFIC; Valencia U↗
NASA NTRS1984

The Soft X-ray Diffuse Background: Implications for the Nature of the Local Interstellar Medium

Observations of the diffuse X-ray background in the B and C bands (130-188 eV and 160-284 eV, respectively) provide convincing evidence for the existence of high-temperature interstellar gas. Since the opacity of normal interstellar material is very high, it is assumed that the soft X-ray flux observed in the galactic plane originates within a few hundred parsecs of the Sun. The intensity and B/C ratio of this low-latitude flux can be provided by emission from an equilibrium plasma with normal abundances, T =10 to the 6th power K, and 0.0019 cm(-6) pc emission measure. More sophisticated nonequilibrium models of material heated by a supernova blast wave would reduce the required emission measure somewhat, but not by so much as a factor of two. Arbitrarily limiting the pressure to 10 to the 4th power cm(-3) K gives a maximum density of 0.005 cm(-3) and a minimum radius for the emitting region of 75 pc. This fits in well with ultraviolet interstellar absorption measurements which indicate that the interstellar medium is very deficient in neutral hydrogen out to approx. 100 pc from the Sun.

Mccammon, D.↗
DOE OSTI2020

Effects of Photonic Curing Processing Conditions on MAPbI 3 Film Properties and Solar Cell Performance

Thermal annealing is the most used postdeposition materials processing method in laboratory research, but due to its slow speed and high energy cost, it is not compatible with the upscaling and commercialization of perovskite solar cell (PSC) manufacturing. Here, we adapt photonic curing (PC), which uses millisecond light pulses to deliver energy to the sample, to replace thermal annealing for crystallization of methylammonium lead iodide (MAPbI 3 ) films and rapid fabrication of PSCs. We study how PC conditions affect the outcome of MAPbI 3 conversion from the precursor to the crystalline perovskite phase by evaluating the films’ optical, crystalline, and morphological properties, as well as PSC performance. The results are understood using simulated film temperature profiles. We show that MAPbI 3 is readily converted under a wide range of PC conditions. While previous reports all used short pulses (<3 ms), we find that longer pulses produce more dense films and higher-performing PSCs. We achieve a champion power conversion efficiency in a PC-processed MAPbI 3 PSC of 11.26% under forward scan and 10.34% under reverse scan, with the processing time for the MAPbI 3 layer reduced by 30,000-fold, from 10 min to 20 ms. Using a 6 in. lamp, spatial uniformity tests show a cross-web efficiency variation of 5%. Our results indicate that using longer pulse lengths, >10 ms, is the best PC strategy for perovskite conversion, and PC is a promising annealing method for large-area, high-throughput PSC manufacturing.

14 SOLAR ENERGY↗
DOE OSTI2021

Bituminous Coal and Natural Gas to Electricity: >90% Capture Cases Technical Note

This technical note provides cost and performance estimates for post combustion carbon capture (PCCC) systems designed for greater than 90 percent capture on conventional PC- and NG-fueled power plants. The cost and performance estimates provided here were developed using the National Energy Technology Laboratory’s (NETL’s) well-documented methodology for conducting technoeconomic analysis of fossil energy conversion systems and leveraging published performance and cost projections for higher capture rate systems. Included in this technical note is a brief description of the method used to adjust select 90 percent capture cases from NETL’s Cost and Performance Baselines for Fossil Energy Systems Volume 1: Bituminous Coal and Natural Gas to Electricity, hereafter referred to as the Baseline Study. This technical note is intended to serve as an interim update to NETL’s Baseline Study cases by providing cost and performance estimates for high capture PCCC technology that can be deployed in the near-term at fossil-fueled electricity generating units.

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1990

Optimal design study of high efficiency indium phosphide space solar cells

Recently indium phosphide solar cells have achieved beginning of life AMO efficiencies in excess of 19 pct. at 25 C. The high efficiency prospects along with superb radiation tolerance make indium phosphide a leading material for space power requirements. To achieve cost effectiveness, practical cell efficiencies have to be raised to near theoretical limits and thin film indium phosphide cells need to be developed. The optimal design study is described of high efficiency indium phosphide solar cells for space power applications using the PC-1D computer program. It is shown that cells with efficiencies over 22 pct. AMO at 25 C could be fabricated by achieving proper material and process parameters. It is observed that further improvements in cell material and process parameters could lead to experimental cell efficiencies near theoretical limits. The effect of various emitter and base parameters on cell performance was studied.

Jain, Raj K.↗
NASA NTRS1992

Statistical discrete particle simulation studies

A particle simulation code was developed that is suited to Multiple Instruction Multiple Data multiprocessor computers. The resulting code is designed to be portable between a large class of multiprocessor computer architectures, including hypercubes (e.g., Intel iPSC/860), shared memory machines (e.g., Cray, SGI, DASH), and simple uniprocessors (e.g., SUN, VAX, IBM PC). This code provides a powerful general framework that can be adapted to specific applications, such as thermomechanical modeling, general 3-D geometry support, or visualization support via a codeveloped CPlot data reduction and visualization system. Chemistry models were implemented and validated with comparison to continuum solutions of thermochemically relaxing gas mixtures and with experimental results from the high speed flow about a circular cylinder. Furthermore, the exchange of energy between translational and internal modes was modeled. New models were developed, combining greater efficiency than earlier phenomenological models. They offer greater physical detail by addressing vibrational energy as a discretely distributed quantity.

Mcdonald, Jeffrey D.↗
NASA NTRS2003

Comparison of Different Methods of Grading a Level Turn Task on a Flight Simulator

With the advancements in the computing power of personal computers, pc-based flight simulators and trainers have opened new avenues in the training of airplane pilots. It may be desirable to have the flight simulator make a quantitative evaluation of the progress of a pilot's training thereby reducing the physical requirement of the flight instructor who must, in turn, watch every flight. In an experiment, University students conducted six different flights, each consisting of two level turns. The flights were three minutes in duration. By evaluating videotapes, two certified flight instructors provided separate letter grades for each turn. These level turns were also evaluated using two other computer based grading methods. One method determined automated grades based on prescribed tolerances in bank angle, airspeed and altitude. The other method used was deviations in altitude and bank angle for performance index and performance grades.

Heath, Bruce E.↗
DOE OSTI2020

Cost and Performance Baseline for Fossil Energy Plants Supplement: Sensitivity to CO 2 Capture Rate In Coal-Fired Power Plants

The cost and performance of various plants designed to meet a range of carbon dioxide (CO 2 ) emission limits are evaluated in this report by varying the CO 2 capture rate. The base cases for these designs are the supercritical (SC) pulverized coal (PC) plant and the General Electric Power (GEP) integrated gasification combined cycle (IGCC) plant from the Department of Energy (DOE) National Energy Technology Laboratory (NETL) report “Cost and Performance Baseline for Fossil Energy Plants, Volume 1: Bituminous Coal and Natural Gas to Electricity, Revision 4” (“Bituminous Baseline”).

20 FOSSIL-FUELED POWER PLANTS↗
NASA NTRS1993

Statistical studies of Pc 3-5 pulsations and their relevance for possible source mechanisms of ULF waves

A number of statistical studies using spacecraft data have been made of ULF waves in the magnetosphere. These studies provide an overview of ULF pulsation activity for r = 5-15 R(E) and allow an assessment of likely source mechanisms. In this review pulsations are categorized into five general types: compressional Pc 5, poloidal Pc 4, toroidal harmonics, toroidal Pc 5 (fundamental mode), and incoherent noise. The occurrence distributions and/or distributions of wave power of the different types suggest that compressional Pc 5 and poloidal Pc 4 derive their energy locally, most likely from energetic protons. The toroidal pulsations, both harmonic and fundamental mode, appear to be driven by an energy source outside the magnetopause - directly upstream in the sheath and solar wind for harmonics and the flanks for fundamentals. Incoherent pulsations are a prominent pulsation type but from their occurrence distribution alone it is unclear what their dominant energy source may be.

Anderson, Brian J.↗
NASA NTRS2020

Chandra and XMM-Newton Observations of A2256: Cold Fronts, Merger Shocks, and Constraint on the IC Emission

We present the results of deep Chandra and XMM-Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic (RR). The temperature and metallicity maps show clear evidence of a merger between the western subcluster (SC) and the primary cluster (PC). We detect five X-ray surface brightness edges. Three of them near the cluster center are cold fronts (CFs): CF1 is associated with the infalling SC; CF2 is located in the east of the PC; and CF3 is to the west of the PC core. The other two edges at cluster outskirts are shock fronts(SFs): SF1 near the RR in the NW has Mach numbers derived from the temperature and the density jumps, respectively, of MT=1.62±0.12 and Mρ=1.23±0.06; SF2 in the SE has MT=1.54±0.05 and Mρ=1.16±0.13. In the region of the RR, there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse-Compton emission, and therefore set a lower limit on the magnetic field (∼450 kpc from PC center) of B>1.0μG for a single power-law electron spectrum or B>0.4μG for a broken power-law electron spectrum. We propose a merger scenario including a PC, an SC, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.

Chong Ge↗
NASA NTRS2020

Chandra and XMM-Newton Observations of A2256: Cold Fronts, Merger Shocks, and Constraint on the IC Emission

We present the results of deep Chandra and XMM-Newton observations of a complex merging galaxy cluster Abell 2256 (A2256) that hosts a spectacular radio relic (RR).The temperature and metallicity maps show clear evidence of a merger between the western subcluster (SC) and the primary cluster (PC). We detect five X-ray surface brightness edges. Three of them near the cluster center are cold fronts (CFs): CF1is associated with the infalling SC; CF2 is located in the east of the PC; and CF3 is to the west of the PC core. The other two edges at cluster outskirts are shock fronts(SFs): SF1 near the RR in the NW has Mach numbers derived from the temperature and the density jumps, respectively, of MT=1.62±0.12andMρ=1.23±0.06; SF2 in the SE has MT=1.54±0.05andMρ=1.16±0.13. In the region of the RR, there is no evidence for the correlation between X-ray and radio substructures, from which we estimate an upper limit for the inverse-Compton emission, and therefore set a lower limit on the magnetic field (∼450 kpc from PC center) of B>1.0μG for a single power-law electron spectrum or B>0.4μG for a broken power-law electron spectrum. We propose a merger scenario including a PC, an SC, and a group. Our merger scenario accounts for the X-ray edges, diffuse radio features, and galaxy kinematics, as well as projection effects.

Chong Ge↗
DOE OSTI2021

Spatial and Kinematic Clustering of Stars in the Galactic Disk

The Galactic disk is expected to be spatially and kinematically clustered on many scales due to both star formation and the Galactic potential. In this work we calculate the spatial and kinematic two-point correlation functions (TPCF) using a sample of 1.7 × 10 6 stars with radial velocities from Gaia DR2. Clustering is detected on spatial scales of 1–300 pc and a velocity scale of 15 km s –1 . After removing bound structures, the data have a power-law index of γ ≈ –1 for 1 pc < Δr < 100 pc and γ ≲ –1.5 for Δr > 100 pc. We interpret these results with the aid of a star-by-star simulation of the Galaxy, in which stars are born in clusters orbiting in a realistic potential that includes spiral arms, a bar, and giant molecular clouds. We find that the simulation largely agrees with the observations at most spatial and kinematic scales. In detail, the TPCF in the simulation is shallower than the data at ≲20 pc scales, and steeper than the data at ≳30 pc. We also find a persistent clustering signal in the kinematic TPCF for the data at large Δv (>5 km s –1 ) that is not present in the simulations. We speculate that this mismatch between observations and simulations may be due to two processes: hierarchical star formation and transient spiral arms. Furthermore, we also predict that the addition of ages and metallicities measured with a precision of 50% and 0.05 dex, respectively, will enhance the clustering signal beyond current measurements.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Life Cycle Cost Analysis of Prestressed Concrete Poles Subjected to Wind, Surges, and Waves

Prestressed concrete (PC) poles are becoming popular choices to support coastal power transmission systems. However, the existing literature does not offer a detailed analysis of the effectiveness of PC poles in terms of long-term vulnerabilities and the direct and indirect costs. This is due to (1) lack of fragility models for PC poles and (2) lack of probabilistic wind, storm surge, and wave models in coastal settings. In this study, we address these gaps through a series of Monte Carlo simulations to estimate fragility of PC poles as a function of age and hazard (wind, surges, and waves) intensity, and the development of a probabilistic hazard model based on 10,000 years of synthetic tropical cyclone data. The probabilistic hazard model is used in conjunction with high-resolution hydrodynamic models to generate realizations of coastal wind, storm surges, and waves for the Louisiana and Mississippi coasts. A comprehensive life cycle cost analysis for a service life of 70 years considering direct and indirect losses is conducted to compare the performance of a transmission line located in Pascagoula, Mississippi, when wood poles are replaced by PC poles. Results showed that aging has a minor effect on the reliability of PC poles, highlighting the advantages of replacing wood poles with PC poles, especially in coastal areas. In addition, PC poles are significantly more cost-effective compared with wood poles over their life cycle, leading to an estimated saving of $11.55 million (68.17% reduction). The results of this study provide key insight to inform decision-making processes to keep the coastal power grids resilient and cost-effective against future storm hazards.

natural disasters↗
NASA NTRS2017

150 kW Class Solar Electric Propulsion Spacecraft Power Architecture Model

The National Aeronautics and Space Administration (NASA) Solar Electric Propulsion Technology Demonstration Mission in conjunction with PC Krause and Associates has created a Simulink-based power architecture model for a 50 kilo-Watt (kW) solar electric propulsion system. NASA has extended this model to investigate 150 kW solar electric propulsion systems. Increasing the power system capability from 50 kW to 150 kW better aligns with the anticipated power requirements for Mars and other deep space explorations. The high-power solar electric propulsion capability has been identified as a critical part of NASAs future beyond-low-Earth-orbit for human-crewed exploration missions. This paper presents multiple 150 kW architectures, simulation results, and a discussion of their merits.

Power Control↗
NASA NTRS2017

150 kW Class Solar Electric Propulsion Spacecraft Power Architecture Model

The National Aeronautics and Space Administration (NASA) Solar Electric Propulsion Technology Demonstration Mission (SEP TDM), in conjunction with PC Krause and Associates, has created a Simulink-based power architecture model for a 50 kilo-Watt (kW) solar electric propulsion system. NASA has extended this model to investigate 150 kW solar electric propulsion systems. Increasing the power capability to 150 kW is an intermediate step to the anticipated power requirements for Mars and other deep space applications. The high-power solar electric propulsion capability has been identified as a critical part of NASA’s future beyond-low-Earth-orbit for human-crewed exploration missions. This paper presents four versions of a 150 kW architecture, simulation results, and a discussion of their merits.

Power Control↗
DOE OSTI2022

High-Fidelity Analysis of ULF Wave Mode Structure Following Interplanetary Shock Compression of the Dayside Magnetopause Using MMS Multi-Point Observations

During the 9 March 2018 event with two consecutive interplanetary shocks compressing the dayside magnetosphere, the azimuthal mode structure and frequency spectrum of ultra low frequency magnetic pulsations are resolved using a cross-spectral analysis based on high-fidelity multi-probe Magnetospheric Multiscale Mission (MMS) magnetometer data. The results based on the MMS 4 and MMS 3 pair of measurements show that shock arrival leads to low mode (|m| ≤ 3) magnetic fluctuations in the Pc4-5 regimes, and smaller spatial scale fluctuations implied by the dominant high mode numbers are observed after both shock signatures hit and passed the magnetosphere. Detailed evolution of the mode structure is also shown for the first shock to reveal the development of high mode structure from a bump-on-tail distribution at m≈20 to a dominant peak at m≈50 in about 10 min. In addition, an interesting change of sign in m from negative to positive is observed as MMS crosses ~11 MLT pre-noon, which is consistent with the picture of wave generation by dayside magnetopause compression and then anti-sunward propagation. Finally, for both shocks, the contribution of higher frequency waves (Pc-4 range compared with Pc-5) to the total wave power is found to be negligible before and after the shock impact, but it becomes more significant during the shock impact.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Early-type stars and the mean-square electron density in the galactic disk.

An assessment is made of the total supply of ionizing photons from hot stars, within several hundred parsecs of the sun. The resulting photoionized H II regions probably contribute an average emission measure of the order of 5 pc per cm to the 6th power, through the galactic disk; this is smaller than other recent estimates.

Richstone, D. O.↗
NASA NTRS1992

Automation of the targeting and reflective alignment concept

The automated alignment system, described herein, employs a reflective, passive (requiring no power) target and includes a PC-based imaging system and one camera mounted on a six degree of freedom robot manipulator. The system detects and corrects for manipulator misalignment in three translational and three rotational directions by employing the Targeting and Reflective Alignment Concept (TRAC), which simplifies alignment by decoupling translational and rotational alignment control. The concept uses information on the camera and the target's relative position based on video feedback from the camera. These relative positions are converted into alignment errors and minimized by motions of the robot. The system is robust to exogenous lighting by virtue of a subtraction algorithm which enables the camera to only see the target. These capabilities are realized with relatively minimal complexity and expense.

Redfield, Robin C.↗