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NASA NTRS1994

The Compton Gamma Ray Observatory

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.↗

NASA NTRS2004

A Ground-Based 200/350 Micrometer Polarization-Sensitive Photometer

We describe a concept for a polarization-sensitive photometer for use at the South Pole and Atacama that employs Transition-Edge Sensor (TES) detectors. We will use two 8x8 element array architecture originally developed at NASA Goddard for a 3 mm camera.for the Green Bank Telescope. The elements will be tuned to have absorption peaks in both the 200 and 350 micron atmospheric windows. This instrument will provide a testbed for three major issues confronting a future far-infrared polarimeter for SOFIA. The first is the TES detector technology. The second is a polarization modulator that can be quickly reconfigured for different passbands. The third is the ability to optimize polarimetric and photometric detection capabilities in the same instrument. Scientifically, this instrument will explore the emission from Galactic star-forming regions in two spectral bands, giving valuable information concerning their spectral energy distributions. Polarimetrically, this instrument will allow coverage of the polarization spectrum for bright Galactic sources, giving new insights into dust grain physics.

Chuss, David T.↗

NASA NTRS2012

Electromagnetic Whistler Precursors at Supercritical Interplanetary Shocks

We present observations of electromagnetic precursor waves, identified as whistler mode waves, at supercritical interplanetary shocks using the Wind search coil magnetometer. The precursors propagate obliquely with respect to the local magnetic field, shock normal vector, solar wind velocity, and they are not phase standing structures. All are right-hand polarized with respect to the magnetic field (spacecraft frame), and all but one are right-hand polarized with respect to the shock normal vector in the normal incidence frame. Particle distributions show signatures of specularly reflected gyrating ions, which may be a source of free energy for the observed modes. In one event, we simultaneously observe perpendicular ion heating and parallel electron acceleration, consistent with wave heating/acceleration due to these waves.

Wilson, L. B., III↗

NASA NTRS2012

Observations of Electromagnetic Whistler Precursors at Supercritical Interplanetary Shocks

We present observations of electromagnetic precursor waves, identified as whistler mode waves, at supercritical interplanetary shocks using the Wind search coil magnetometer. The precursors propagate obliquely with respect to the local magnetic field, shock normal vector, solar wind velocity, and they are not phase standing structures. All are right-hand polarized with respect to the magnetic field (spacecraft frame), and all but one are right-hand polarized with respect to the shock normal vector in the normal incidence frame. They have rest frame frequencies f(sub ci) < f much < f(sub ce) and wave numbers 0.02 approx < k rho (sub ce) approx <. 5.0. Particle distributions show signatures of specularly reflected gyrating ions, which may be a source of free energy for the observed modes. In one event, we simultaneously observe perpendicular ion heating and parallel electron acceleration, consistent with wave heating/acceleration due to these waves. Al though the precursors can have delta B/B(sub o) as large as 2, fluxgate magnetometer measurements show relatively laminar shock transitions in three of the four events.

Wilson, L. B., III↗

NASA NTRS2013

The Prediction of Jet Noise Ground Effects Using an Acoustic Analogy and a Tailored Green's Function

An assessment of an acoustic analogy for the mixing noise component of jet noise in the presence of an infinite surface is presented. The reflection of jet noise by the ground changes the distribution of acoustic energy and is characterized by constructive and destructive interference patterns. The equivalent sources are modeled based on the two-point cross- correlation of the turbulent velocity fluctuations and a steady Reynolds-Averaged Navier-Stokes (RANS) solution. Propagation effects, due to reflection by the surface and refaction by the jet shear layer, are taken into account by calculating the vector Green's function of the linearized Euler equations (LEE). The vector Green's function of the LEE is written in relation to Lilley's equation; that is, approximated with matched asymptotic solutions and the Green's function of the convective Helmholtz equation. The Green's function of the convective Helmholtz equation for an infinite flat plane with impedance is the Weyl-van der Pol equation. Predictions are compared with an unheated Mach 0.95 jet produced by a nozzle with an exit diameter of 0.3302 meters. Microphones are placed at various heights and distances from the nozzle exit in the peak jet noise direction above an acoustically hard and an asphalt surface. The predictions are shown to accurately capture jet noise ground effects that are characterized by constructive and destructive interference patterns in the mid- and far-field and capture overall trends in the near-field.

Miller, Steven A. E.↗

NASA NTRS2023

Rapid transition from primary to secondary crust building on the Moon explained by mantle overturn

Geochronology indicates a rapid transition (tens of Myrs) from primary to secondary crust building on the Moon. The processes responsible for initiating secondary magmatism, however, remain in debate. Here we test the hypothesis that the earliest secondary crust (Mg-suite) formed as a direct consequence of density-driven mantle overturn, and advance 3D mantle convection models to quantify the resulting extent of lower mantle melting. Our modeling demonstrates that overturn of thin ilmenite-bearing cumulates ≤ 100 km triggers a rapid and short-lived episode of lower mantle melting which explains the key volume, geochronological, and spatial characteristics of early secondary crust building without contributions from other energy sources, namely KREEP (potassium, rare earth elements, phosphorus, radiogenic U, Th). Observations of globally distributed Mg-suite eliminate degree-1 overturn scenarios. We propose that gravitational instabilities in magma ocean cumulate piles are major driving forces for the onset of mantle convection and secondary crust building on differentiated bodies.

Moon↗

DOE OSTI2020

NREL CITIES Support (CRADA CRD-14-00558 Final Report)

The Technical University of Denmark has received a Grant from the Danish Council for Strategic Research for the project "CITIES - Centre for IT-Intelligent Energy Systems in Cities", a strategic research centre, which involves industrial partners and universities. The Alliance for Sustainable Energy, LLC will participate with DTU as an industrial partner in "CITIES" under this Cooperative Research and Development Agreement (CRADA). The Centre for IT based Intelligent Energy Systems in Cities (CITIES) Project is a Danish national research center focused on work in building short-term operational integrated energy system models that feed longer term plam1ing models, considering the spatio-temporal variations, interactions, dynamics and stochastics in the energy system, from production to consumption. CITIES will harness the extensive expertise and experience of its industrial and academic partners to conduct meaningful research with tangible outputs, including a roadmap to a fossil free future. Decision support tools will be developed to inform stakeholders of the impact of investment, control and policy measures and to identify further opportunities for energy system efficiency. Dissemination and transferring knowledge is a key value to this CRADA, and the use of results by Danish policymakers, industry and society is vital. All participants in the Centre for IT based Intelligent Energy Systems in Cities (CITIES) Project are therefore encouraged to use all means to communicate their findings to society. Wherever possible, and compatible with applicable intellectual property regulations, publications should be produced and disseminated under Open Science, Data, Source and Access principles.

24 POWER TRANSMISSION AND DISTRIBUTION↗

DOE OSTI2023

A Review of Distributed Secondary Control Architectures in Islanded-Inverter-Based Microgrids

The increasing energy demand, the shortage of energy resources, and the environmental challenges faced by conventional power-generation systems are some of the ongoing challenges faced by modern power systems. Therefore, many efforts have been made by the scientific community to develop comprehensive solutions to overcome these issues. For instance, current technological advances have allowed the integration of distributed generators into the power systems, promoting the use of microgrids to overcome these issues. However, the use of renewable distributed generators have introduced new challenges to the traditional control system schemes. To overcome these challenges, a hierarchical control approach has been proposed for distributed renewable sources. In other words, the control scheme have been divided into three hierarchical levels, primary, secondary, and tertiary, to overcome the new challenges present in modern power systems. Due to extensiveness of this topic, this overview is focused on secondary control systems, mainly for AC isolated microgrids. To improve the power quality of modern systems, several secondary control schemes have been proposed to overcome the well-known problem of frequency and voltage deviation. Some of these schemes have also introduced adequate active/reactive power sharing techniques to optimize the utilization of resources. Additionally, other secondary control schemes have also focused on reducing the communication load, to lower the network cost and adding robustness against communication problems. This article presents an insight of the different control techniques used to overcome power quality and communication problems. A comprehensive overview of distributed secondary control techniques for islanded microgrids is presented. In addition, the implementation of these techniques is explained in an orderly and sequential manner.

14 SOLAR ENERGY↗

NASA NTRS1985

Some evidence for high energy gamma-ray sources at large galactic latitudes

The arrival directions of the gamma-quanta with energies of about 10 to 15th power eV which were registrated by Tien Shan experiment were compared with COS-B observations. On the basis of the Monte Carlo simulations it was shown with low probability that arrival directions of Tien Shan gamma-quanta initiated showers are not uniformly distributed. It is shown that in the region not seen by COS-B mission, the high energy gamma-ray sources should be located at position of 90 deg. 1 sup 11 130 deg and b sup 11 or = 50 deg. The integral intensity of these sources should be I ( 10 to the 15th power eV) = 4.8 + or - 1.7).10 to the 13th power/sq cm/s/str. There is no coincidence between the gamma-quanta registrated by Tien Shan experiment with Geminga intense COS-B gamma source. So it is shown that the integral photon spectrum of Geminga (I(e) approx E sup-Beta, where Beta = 0.8 for E 1 GeV) becomes steeper (Beta 1.2) in high energy region with probability 99.9.%.

Karakula, S.↗

NASA NTRS1998

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the entire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function, and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8)eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Khazanov, G. V.↗

DOE OSTI2025

Clustering redshift distribution calibration of weak lensing surveys using the DESI-DR1 spectroscopic dataset

We estimate the source redshift distribution of current weak lensing surveys by applying the clustering-based redshift calibration technique, using the galaxy redshift sample provided by the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1). We cross-correlate the Bright Galaxy Survey (BGS), Luminous Red Galaxies (LRGs) and Emission Line Galaxies (ELGs) from DESI, within the redshift range $0.1 < z < 1.6$, with overlapping tomographic source samples from the Dark Energy Survey (DES), Kilo-Degree Survey (KiDS), and Hyper Suprime-Cam (HSC) survey. Using realistic mock catalogues, we test the stability of the clustering-redshift signal to fitting scale, reference-sample choice, and the evolution of source galaxy bias, and we explicitly model and marginalise over magnification contributions, which become non-negligible at $z \gtrsim 1$ due to the depth of the DESI ELG sample. We then compare the resulting bias-weighted redshift distributions to those calibrated using self-organising map (SOM) techniques, finding agreement within uncertainties for all surveys and tomographic bins. Our results demonstrate that clustering redshifts enabled by DESI's unprecedented spectroscopic sample provides a robust, complementary, and independent constraint capable of reducing one of the dominant systematic uncertainties in weak lensing cosmology.

Ruggeri, R. [Queensland U.]↗

NASA NTRS1970

Code CUGEL: A code to unfold Ge(Li) spectrometer polyenergetic gamma photon experimental distributions

A FORTRAN code was developed for the Univac 1108 digital computer to unfold lithium-drifted germanium semiconductor spectrometers, polyenergetic gamma photon experimental distributions. It was designed to analyze the combination continuous and monoenergetic gamma radiation field of radioisotope volumetric sources. The code generates the detector system response matrix function and applies it to monoenergetic spectral components discretely and to the continuum iteratively. It corrects for system drift, source decay, background, and detection efficiency. Results are presented in digital form for differential and integrated photon number and energy distributions, and for exposure dose.

Steyn, J. J.↗

NASA NTRS1998

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the en- tire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8) eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Khazanov, G. V.↗

NASA NTRS1986

The cosmic-ray source composition

The cosmic-ray source composition is shown to be related to the observed cosmic-ray abundances by a set of linear equations which are valid for either ad hoc path length distributions or quantitative solutions of galactic propagation models. In the limit of no ionization energy loss, this method is exact for all path length distributions and can replace more detailed numerical integrations; it provides a simple way to calculate directly the source composition implied by a particular set of cross sections, observed abundances, and propagation model. This method is used to determine the source abundances of the galactic cosmic rays in a model-independent manner. Compared to a simple exponential, the path length distribution required by observations is deficient in the contributions from short (not greater than 0.5 g/sq cm) paths at energies of a few GeV per nucleon.

Margolis, S. H.↗

NASA NTRS2004

Simulations of Hyperthermal Oxygen Beam Exposures

Pulsed sources of hyper-thermal O-atoms are now being extensively used to simulate low-earth orbit (LEO) surface exposure environments. The peak flux of these sources is many orders of magnitude larger than the corresponding LEO flux. Although it is desirable to accelerate the test by using higher fluxes than found in LEO, even commonly used fluxes are large enough to produce multi-collision effects by causing a build-up of gas at the sample surface. In this paper we characterize the physical consequences to the experiment using the direct simulation Monte Carlo (DSMC) method, DSMC allows us to extract the distributions of energy and impact angle for the O-atoms that reach the surface, and to record how strongly the gas build-up at the target assembly deflects flux from downstream instrumentation. By considering a range of source fluxes, we determine the onset conditions and severity of these multi-collision effects. We find that even at common experimental fluxes with a normally incident beam string a flat surface sample, the energy distribution of incident O-atoms broadens and develops a significant low-energy tail. The angular distributions also broaden significantly. The number of O-atoms that reach downstream instrumentation is decreased by approximately 50%. These simulations will aid in the calibration of ground-based O-atom measurements,a nd provide a model for the energy and angular distributions of O-atoms that actually impinge on surface samples.

Finchum, A.↗

NASA NTRS2003

DSMC Simulations of Hyperthermal Oxygen Beam Exposures

Pulsed sources of hyper-thermal O-atoms are now being extensively used to simulate low-earth orbit (LEO) surface exposure environments. The peak flux of these sources is many orders of magnitude larger than the corresponding LEO flux. Although it is desirable to accelerate the test by using higher fluxes than found in LEO, even commonly used fluxes are large enough to produce multi-collision effects by causing a build-up of gas at the sample surface. In this paper we characterize the physical consequences to the experiment using the direct simulation Monte Carlo (DSMC) method. DSMC allows us to extract the distributions of energy and impact angle for the O-atoms that reach the surface, and to record how strongly the gas build-up at the target assembly deflects flux from downstream instrumentation. By considering a range of source fluxes, we determine the onset conditions and severity of these multi-collision effects. We find that even at common experimental fluxes with a normally incident beam striking a flat surface sample, the energy distribution of incident O-atoms broadens and develops a significant low-energy tail. The angular distributions also broaden significantly. The number of O-atoms that reach downstream instrumentation is decreased by approximately 50%. These simulations will aid in the calibration of ground-based O-atom measurements, and provide a model for the energy and angular distributions of O-atoms that actually impinge on surface samples.

Cline, Jason A.↗

DOE OSTI2024

Hydrogen Leak Modeling for Development of Smart Distributed Monitoring Under Unintended Releases

Hydrogen is a versatile and clean energy carrier that can be produced from various renewable sources such as wind, solar, and hydropower. Hydrogen has the potential to play a crucial role in decarbonizing industrial processes that are currently reliant on fossil fuels and provide long-duration and/or seasonal energy storage to enable electricity decarbonization. Hydrogen can also be used as a fuel for fuel cell vehicles, providing a zero-emission alternative to traditional internal combustion engines. DOE launched the Hydrogen Energy Earthshot (Hydrogen Shot) in June 2021 to reduce the cost of clean hydrogen by 80% to $1 per 1 kilogram in 1 decade ("1 1 1"). While promising, Hydrogen is highly-flammable, and in the presence of oxygen, it can form explosive mixtures. . Therefore, understanding leak scenarios is essential to evaluate and mitigate the safety risks associated with potential hydrogen leaks. An increased understanding of leak behavior, and having tools to model leaks, can help assess how hydrogen would disperse in different environments, influencing emergency response plans and safety measures, and identify potential issues with materials and design systems that can withstand the challenges posed by hydrogen. Recently, researchers have attempted to study hydrogen leaks for development of risk management strategies. However, the focus has been on closed or semi-closed spaces like storage rooms, vehicles, garages, and fueling stations - all promising locations for future hydrogen infrastructure. In this presentation, the modeling environment extends the span of research further by modeling hydrogen leak in an outdoor, open space. We will present the key challenges with modeling hydrogen leaks in an uncontrollable environment, how they were handled, and how modeling results informed sensor selection and placement. A Hydrogen research facility at the National Renewable Energy Laboratory (NREL) was used as a case study to model hydrogen leaks. In the future, Hydrogen wide area detection methodologies will be developed and tested at this site to monitor for unintended and operational hydrogen releases. The data generated from modeling will be used to develop a predictive model to detect hydrogen leak location based on concentration measured by sensors in this open space. Furthermore, the facility was also chosen because controlled hydrogen releases can be performed. A computational fluid dynamics (CFD) based modeling approach was taken to model hydrogen leak. The full-scale hydrogen facility was modeled with a large ambient domain. The electrolyzer at the facility can produce a controlled release rate of 27 kg-H2/hr. Site-specific atmospheric and weather condition data such as wind direction, wind speed at various altitudes, and temperature were used as inputs to the model. To capture the variability of weather conditions, a subset of the weather conditions experienced during daytime hours without precipitation over the course of three months was generated; using established data clustering techniques, a total of 100 condition sets were chosen. The results show statistical distributions and ranges of hydrogen concentrations at locations throughout the domain. These distributions are compared to experimental data from a constant mass flow, controlled hydrogen release at the facility. The stochastic wind conditions of the release make direct validation difficult, therefore, statistical comparison approaches were used. Wind conditions are found to significantly impact the release behavior, including direction and concentration. Sensor selection and placement is proposed for the facility and is now based on release behavior predicted for the facility given its weather patterns; this is much more informed than without the modeling results. The methodology and analysis procedure can be translated to other facilities using modified geometries and site-specific weather conditions. Hydrogen holds great promise as a renewable energy fuel, but ensuring safety in its production, storage, and use is paramount. Studying potential leak scenarios in an open space will help develop sensors to detect hydrogen on a large spectrum of concentration and eventually build a smart distributed monitoring system.

CFD↗

NASA NTRS2004

Rest-Frame Mid-Infrared Detection of an Extremely Luminous Lyman Break Galaxy with the Spitzer Infrared Spectrograph (IRS)

We present the first rest-frame of approximately 4 microns detection of a Lyman break galaxy. The data were obtained using the 16 microns imaging capability of the Spitzer Infrared Spectrograph. The target object, J134026.44+634433.2, is an extremely luminous Lyman break galaxy at z=2.79, first identified in Sloan Digital Sky Survey (SDSS) spectra (as reported by Bentz et al.). The source is strongly detected with a flux of 0.94 +/- 0.02 mJy. Combining Spitzer and SDSS photometry with supporting ground-based J- and K-band data, we show that the spectral energy distribution is consistent with an actively star-forming galaxy. We also detect other objects in the Spitzer field of view, including a very red mid-infrared source. We find no evidence of a strong lens among the mid-infrared sources.

cosmology↗