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At least 469 records · Page 26

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NASA NTRSDate not supplied

Impact of Radiation Quality on Microdosimetry Calculation

Microdosimetry consists of studying energy deposition events in irradiated targets of volume typically of the order of a cell. The probability density 𝑓(𝑧,𝐷) of energy deposition𝑧(specific energy) in a target, exposed to an irradiation dose 𝐷,can be used to correlate inhomogeneous energy deposition events at the micro-scale(track structure)with biological responses(e.g., cell injury)[1]. Microdosimetry studies allow a better understanding of basic mechanisms of the biological response, such as the origin of the increased biological effectiveness of high Linear Energy Transfer (LET) ions, partly responsible of radiation-exposure induced cancer risks of astronauts [2].

F. Poignant↗

DOE OSTI2022

NRC Reactor Operating Experience Analysis and Trend Summary: 2020 Update

This report presents a summary of the reliability and frequency trends identified in the 2020 update reports for component performance study, loss of offsite power analysis, initiating events analysis, and system study provided on the Nuclear Regulatory Commission (NRC) Reactor Operating Experience Results and Databases web site (https://nrcoe.inl.gov/).

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2024

NRC Reactor Operating Experience Analysis and Trend Summary: 2022 Update

This report presents a summary of the Nuclear Regulatory Commission (NRC) reactor operating experience analyses with data through 2022 as well as the reliability and frequency trends identified in the 2022 update reports for component performance study, loss of offsite power analysis, initiating events analysis, and system study provided on the NRC Reactor Operating Experience Results and Databases website (https://nrcoe.inl.gov/).

99 GENERAL AND MISCELLANEOUS↗

NASA NTRS2007

Digital Learning Network Education Events for the Desert Research and Technology Studies

NASA s Digital Learning Network (DLN) reaches out to thousands of students each year through video conferencing and webcasting. As part of NASA s Strategic Plan to reach the next generation of space explorers, the DLN develops and delivers educational programs that reinforce principles in the areas of science, technology, engineering and mathematics. The DLN has created a series of live education videoconferences connecting the Desert Research and Technology Studies (RATS) field test to students across the United States. The programs are also extended to students around the world via live webcasting. The primary focus of the events is the Vision for Space Exploration. During the programs, Desert RATS engineers and scientists inform and inspire students about the importance of exploration and share the importance of the field test as it correlates with plans to return to the Moon and explore Mars. This paper describes the events that took place in September 2006.

Paul, Heather L.↗

NASA NTRS2007

CMEs and Low Density Events in the Solar Wind

From time to time the density of the Solar Wind falls below unity for a day or so. Despite studies of these events, their cause has not been established. In the solar wind there are frequent rarefactions but these are much shallower than the ones we are discussing here. In particular any role that CMEs might play in forming more extreme rarefactions is not clear . We discuss 9 cases of extreme events, leading to sub-alfvenic flow and well observed by Wind, which occurred between 1999 and 2002, and look for corresponding CME events in the LASCO cotalog. The catalog gives a fitted speed , good out to 20 Rs ,as well as a speed lower down in the corona, and this is used to distinguish between a CME and an ICME. We find one of the events ,which was simulated by Usmanov et al.,cannot be associated with an ICME. The other eight events can plausibly be associated with fast ICMEs, identified by the prescence of bi-streaming electrons also seen by Wind SWE, and by other phenomena The implications of these observations are discussed but do not seem to be conclusive as to the cause of the extreme rarefactions.

Ogilvie, K. W.↗

NASA NTRS1986

Gyrating and intermediate ion distributions upstream from the earth's bow shock

Study of ISEE 2 fast plasma data reveals that many suprathermal ion events that in previous studies would have been identified as intermediate ion events are actually gyrating ion events. Of 190 apparently intermediate ion events selected on the basis of their signature in energy-time spectrograms, half are actually found to be gyrating ion events. Using a model bow shock, the shock geometries and spacecraft locations for the observed gyrating and intermediate ion events are compared and found to be quite similar. Both gyrating and intermediate ion events are found to be associated with upstream MHD-like wave activity. Most gyrating ion events are associated with large-amplitude, monochromatic, weakly compressive waves, whereas many intermediate ion events are associated with smaller-amplitude, nonmonochromatic, weakly compressive waves. Some intermediate ion events are found to have no associated waves. Detailed study of the gyrating ion distributions reveals that the distributions are typically gyrotropic within about 4 earth radii of the bow shock, whereas at larger distances (up to about 10 earth radii) upstream from the shock the distributions are frequently 'gyrophase bunched'. In light of these observational characteristics, it is concluded that gyrating ion distributions are most likely generated both through coherent wave disruption of field-aligned beams and through reflection of solar wind ions off the shock.

Fuselier, S. A.↗

NASA NTRS2012

Simulations of Magnetic Reconnection - Kinetic Mechanisms Underlying the Fluid Description of Ions

Because of its ability to transfer the energy stored in magnetic field together with the breaking of the flux freezing constraint, magnetic reconnection is considered as one of the most important phenomena in plasma physics. When it happens in a collision less environment such as the terrestrial magnetosphere, it should a priori be modelled with in the framework of kinetic physics. The evidence of kinetic features has incidentally for a long time, been shown by researchers with the help of both numerical simulations and satellite observations. However, most of our understanding of the process comes from the more intuitive fluid interpretation with simple closure hypothesis which do not include kinetic effects. To what extent are these two separate descriptions of the same phenomenon related? What is the role of kinetic effects in the averaged/fluid dynamics of reconnection? This thesis addresses these questions for the proton population in the particular case of anti parallel merging with the help of 2D Hybrid simulations. We show that one can not assume, as is usually done, that the acceleration of the proton flow is only due to the Laplace force. Our results show, for symmetric and asymmetric connection, the importance of the pressure force, opposed to the electric one on the separatrices, in the decoupling region. In the symmetric case, we emphasize the kinetic origin of this force by analyzing the proton distribution functions and explain their structure by studying the underlying particle dynamics. Protons, as individual particles, are shown to bounce in the electric potential well created by the Hall effect. The spatial divergence of this well results in a mixing in phase space responsible for the observed structure of the pressure tensor. A detailed energy budget analysis confirms the role of the pressure force for the acceleration; but, contrary to what is sometimes assumed, it also reveals that the major part of the incoming Poynting flux is transferred to the thermal energy flux rather than to the convective kinetic energy flux, although the latter is generally supposed dominant. In the symmetric case, we propose the pressure tensor to be an additional proxy of the ion decoupling region in satellite data and verify this suggestion by studying a reconnection event encountered by the Cluster spacecrafts. Finally, the last part of this thesis is devoted to the study of the kinetic structure of asymmetric tangential current sheets where connection can develop. This theoretical part consists in finding a steady state solution to the Vlasov-Maxwell system for the protons in such a configuration. We present the theory and its first confrontation to numerical tests.

Aunai, icolas↗

NASA NTRS1986

Electric and magnetic observations of the structure of standing waves in the magnetosphere

Electric and magnetic field instruments on the DE 1 spacecraft provided observations of toroidal standing wave oscillations of magnetic shells in 1981 and 1982. The amplitude and nodal structure of these waves, as a function of increasing magnetic latitude, was studied and compared with model calculations of these waves. Eight pulsation events were selected for study. The pulsations in these events ranged in period from 20 to 300 s. They were observed at L values between 2.8 and 9.7 and at magnetic latitudes from the equator to 48 deg. The duration of these pulsation events was 20 to 30 min, and they usually consisted of a 5- to 10-min growth in amplitude, a 5- to 10-min interval of fluctuating amplitude, and a 5- to 20-min interval of decreasing amplitude. The relative E and B amplitudes and the phase relations between the E and B waves could be qualitatively explained by the nodal structure of the waves predicted by model calculations. Detailed quantitative comparisons of E and B amplitudes were in agreement with more recent model calculations. In a few cases, electron densities were also available as derived from plasma frequency observations; in these cases the standing wave periods calculated were reasonably close to, but somewhat less than, the observed periods.

Cahill, L. J., Jr.↗

NASA NTRS1982

Plasma behavior during energetic electron streaming events further evidence for substorm-associated magnetic reconnection

A recent study showed that streaming energetic (more than 200 keV) electrons in earth's magnetotail are statistically associated with southward magnetic fields and with enhancements of the AE index. It is shown here that the streaming electrons characteristically are preceded by an approximately 15-minute period of tailward plasma flow and followed by a dropout of the plasma sheet, thus demonstrating a clear statistical association between substorms and the classical signatures of magnetic reconnection and plasmoid formation. Additionally, a brief upward surge of mean electron energy preceded plasma dropout in several of the events studied, providing direct evidence of localized, reconnection-associated heating processes.

Bieber, J. W.↗

DOE OSTI2023

Super-Resolution for Renewable Energy Resource Data with Climate Change Impacts (Sup3rCC)

The Super-Resolution for Renewable Energy Resource Data with Climate Change Impacts (Sup3rCC) data is a collection of 4km hourly wind, solar, temperature, humidity, and pressure fields for the contiguous United States under various climate change scenarios. Sup3rCC is downscaled Global Climate Model (GCM) data. The downscaling process was performed using a generative machine learning approach called sup3r: Super-Resolution for Renewable Energy Resource Data (linked below as "Sup3r GitHub Repo"). The data includes both historical and future weather years, although the historical years represent the historical climate, not the actual historical weather that we experienced. You cannot use Sup3rCC data to study historical weather events, although other sup3r datasets may be intended for this. The Sup3rCC data is intended to help researchers study the impact of climate change on energy systems with high levels of wind and solar capacity. Please note that all climate change data is only a representation of the possible future climate and contains significant uncertainty. Analysis of multiple climate change scenarios and multiple climate models can help quantify this uncertainty.

Array↗

NASA NTRS1979

A study of magnetosphere dynamics during auroral electrojet events by observations of energetic electron intensity changes at synchronous orbit

The central theme of the considered investigation is the surprising detailed correlation between dynamical changes in electron directional intensity measurements at synchronous orbit and the auroral electrojet currents in the polar ionosphere. The statistical study reported has been carried out following the discovery by Erickson and Winckler (1973) of a close relationship between the time profiles of auroral electrojet intensifications and electron intensity decreases observed in the pre-midnight sector at synchronous orbit. The electron data used in the study were obtained during 1967 and 1968 by the University of Minnesota magnetic spectrometer carried onboard ATSl.

Erickson, K. N.↗

NASA NTRS1984

Association between energetic particle bursts and Birkeland currents in the geomagnetic tail

IMP 8 observations in the geomagnetic tail of energetic particles at hundreds of keV and of the magnetic field are examined for a substorm period from 1700 to 1800 UT on Mar. 3, 1976. For this interval, it is found that bursts of energetic protons detected at a downstream distance of about 37 earth radii in the midnight tail region are accompanied by east-west magnetic field perturbations indicative of Birkeland current sheets. The magnitude of the magnetic field perturbations range from about 1 to 12 nT, corresponding to current densities of 1 to 9 mA/m when integrated over the current sheet thickness. These values are comparable to previous observations of Birkeland currents in the near-earth tail (X greater than -20 earth radii) and with the auroral-arc-associated Birkeland current densities at low altitudes scaled out to the tail region. The favorable comparison suggests that the closure of small-scale Birkeland current systems, at least in these instances, lies tailward of about 40 earth radii. The observed Birkeland current system and the magnitude of current densities are found to be consistent with ion tearing instability in the tail. The inferred wavelength of the tearing mode along the tail axis is about 2 to 17 earth radii. In the context of the tearing model, the presence of Birkeland currents and the occasional isotropic distribution of energetic electrons (of more than 0.22 MeV) suggest that the energetic particle events in this study occur on closed magnetic field lines, even though strong tailward streaming dominates the particle anisotropy in these events.

Lui, A. T. Y.↗

NASA NTRS2002

Atmospheric Science Research Using Raman Lidar at NASA/GSFC

A broad overview of the research that is taking place in the Code 924 Raman Lidar group will be presented. The measurement capabilities of two instruments, the Scanning Raman Lidar (SRL) and the Raman Airborne Spectroscopic Lidar (RASL), will be discussed. Case studies to be presented include: 1) high resolution measurements of water vapor during a boundary layer bore wave event; 2) a study of the influence of thin cirrus clouds on satellite retrievals of water vapor; 3) the retrieval of warm cloud properties such as droplet radius and number density; and 4) remote aerosol characterization using multiwavelength lidar and others.

Whiteman, David N.↗

DOE OSTI2021

Correlations between emission events in Rainbow Gravity

Highlights: • It is studied emission correlations between particle emission events in black holes. • Particles emitted have highly correlated moments before the BH stops radiating. • Rainbow Gravity allows maintaining the rest of it stored in its remnant. In this work, we study emission correlations in Rainbow Gravity (RG) black holes known to have black hole remnants. Non-thermal corrections are responsible for generating non-zero correlations between particle emission events during the black hole evaporation process. With this in mind, we calculate the temperatures considering back-reaction effects. Then, we obtain the correlations between emission events for a RG metric proposed by Magueijo and Smolin. We also discuss through a numerical analysis the emission correlations behavior in the last stages of evaporation of the black hole.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2024

The kinetics of SARS-CoV-2 infection based on a human challenge study

Studying the early events that occur after viral infection in humans is difficult unless one intentionally infects volunteers in a human challenge study. Here, we use data about severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in such a study in combination with mathematical modeling to gain insights into the relationship between the amount of virus in the upper respiratory tract and the immune response it generates. We propose a set of dynamic models of increasing complexity to dissect the roles of target cell limitation, innate immunity, and adaptive immunity in determining the observed viral kinetics. We introduce an approach for modeling the effect of humoral immunity that describes a decline in infectious virus after immune activation. We fit our models to viral load and infectious titer data from all the untreated infected participants in the study simultaneously. We found that a power-law with a power h < 1 describes the relationship between infectious virus and viral load. Viral replication at the early stage of infection is rapid, with a doubling time of ~2 h for viral RNA and ~3 h for infectious virus. We estimate that adaptive immunity is initiated ~7 to 10 d postinfection and appears to contribute to a multiphasic viral decline experienced by some participants; the viral rebound experienced by other participants is consistent with a decline in the interferon response. Altogether, we quantified the kinetics of SARS-CoV-2 infection, shedding light on the early dynamics of the virus and the potential role of innate and adaptive immunity in promoting viral decline during infection.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS2011

Astronaut Health Participant Summary Application

The Longitudinal Study of Astronaut Health (LSAH) Participant Summary software captures data based on a custom information model designed to gather all relevant, discrete medical events for its study participants. This software provides a summarized view of the study participant s entire medical record. The manual collapsing of all the data in a participant s medical record into a summarized form eliminates redundancy, and allows for the capture of entire medical events. The coding tool could be incorporated into commercial electronic medical record software for use in areas like public health surveillance, hospital systems, clinics, and medical research programs.

Johnson, Kathy↗

DOE OSTI2022

Maritime Aerosol and CCN Profiles Derived From Ship₋Based Measurements Over Eastern North Pacific During MAGIC

Atmospheric aerosols are widely recognized to give rise to a substantial radiative forcing to the climate by scattering and absorbing radiation and by modifying the microphysical, lifetime, and radiative properties of clouds. During the Marine ARM GPCI Investigation of Clouds (MAGIC) over the Eastern North Pacific (ENP), the ship-based measured cloud condensation nuclei (CCN) concentration at 0.2% supersaturation (N CCN,0.2 ) and condensation nuclei concentration (N CN ) had mean values of 116.7 and 219.4 cm ⁻3 , with the highest concentrations found closest to LA due to an increase in aerosol sources. Moving westward, both N CCN,0.2 and N CN gradually decreased until stabilizing near 100 cm ⁻3 and 200 cm ⁻3 , respectively. Using the methods proposed by Ghan and Collins (2004), https://doi.org/10.1175/1520-0426(2004)021<0387:uoisdt>2.0.co;2 and Ghan et al. (2006), https://doi.org/10.1029/2004jd005752, N CCN,0.2 profiles are retrieved using the surface measured N CCN,0.2 as a constraint. For coupled conditions, correlations between the retrieved N CCN,0.2 profiles and cloud-droplet number concentration (N C ) increase from 0.26 at the surface to 0.38 near cloud base, particularly true for non-drizzling clouds. Although the correlations are lower than expected, the percentage increase (46.2%) is encouraging. Finally, the relationships between cloud breakup (CB) and the stratocumulus to cumulus transition (SCT) with environmental conditions and associated aerosols are also studied. The decreased N CN trend east of CB is mainly caused by precipitation scavenging, while the increased N CN trend west of CB is strongly associated with the increased surface wind speed and fewer drizzle events. A further study is needed using high-resolution models to simulate these events.

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1986

Coronal mass ejections and coronal structures

Research on coronal mass ejections (CMF) took a variety of forms, both observational and theoretical. On the observational side there were: case studies of individual events, in which it was attempted to provide the most complete descriptions possible, using correlative observations in diverse wavelengths; statistical studies of the properties CMEs and their associated activity; observations which may tell us about the initiation of mass ejections; interplanetary observations of associated shocks and energetic particles even observations of CMEs traversing interplanetary space; and the beautiful synoptic charts which show to what degree mass ejections affect the background corona and how rapidly (if at all) the corona recovers its pre-disturbance form. These efforts are described in capsule form with an emphasis on presenting pictures, graphs, and tables so that the reader can form a personal appreciation of the work and its results.

Hildner, E.↗