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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Coacervate-like microspheres from lysine-rich proteinoid

Microspheres form isothermally from lysine-rich proteinoid when the ionic strength of the solution is increased with NaCl or other salts. Studies with different monovalent anions and with polymers of different amino acid composition indicate that charge neutralization and hydrophobic bonding contribute to microsphere formation. The particles also form in sea water, especially if heated or made slightly alkaline. The microspheres differ from those made from acidic proteinoid but resemble coacervate droplets in some ways (isothermal formation, limited stability, stabilization by quinone, uptake of dyes). Because the constituent lysine-rich proteinoid is of simulated prebiotic origin, the study is interpreted to add emphasis to and suggest an evolutionary continuity for coacervation phenomena.

Rohlfing, D. L.↗
NASA NTRS1976

Electromagnetic scattering from a spherical polydispersion of coated spheres

The volume averaged cross sections for extinction, scattering, absorption, and radiation pressure along with the elements of the phase matrix were computed for a spherical polydispersion of water coated carbon particles. The wavelength used was 4910 A. The thickness of the water coating was held constant over the polydispersion, while the ratio of core radius to total radius was varied, or the ratio was held constant over the polydispersion, while the thickness of the coating varied. The results show large differences in both the intensity and degree of polarization between dry and wet aerosols. Also interference phenomena can occur, which demonstrate that the assignment of an average refractive index to aerosols can be misleading and can lead to erroneous results.

Kattawar, G. W.↗
NASA NTRS1984

Evidence of magnetic merging from low-altitude spacecraft and ground-based experiments

Magnetic-reconstruction models of magnetospheric phenomena and the airborne and ground-based measurement data supporting such models are reviewed and illustrated with diagrams and graphs. The primary emphasis is on the correlation of east-west flows on the dayside with the y component of the interplanetary magnetic field (IMF), and consideration is given to z-component IMF effects, magnetospheric convection for a northward IMF, and evidence based on particle distributions.

Reiff, P. H.↗
NASA NTRS1989

Man-made transients observed by the gamma-ray spectrometer on the Solar Maximum Mission satellite

Since launch in early 1980 the gamma-ray spectrometer (GRS) on SMM has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation-belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 sec to more than 10 min. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: 511-keV annihilation-line events, particle events, and broad-band photon continuumlike events. It is found that the most likely sources of these events are reactors in earth-orbiting satellites.

Rieger, Erich↗
NASA NTRS1996

Ion Acceleration in Solar Flares

Solar flares are among the most energetic and interesting phenomena in the Solar system, releasing up to 1032 ergs of energy on timescales of several tens of seconds to several tens of minutes. Much of this energy is in the form of suprathermal electrons and ions, which remain trapped at the Sun and produce a wide variety of radiations, as well as escape into interplanetary space, where they can be directly observed. The radiation from trapped particles consists in general of (1) continuum emission; (2) narrow gamma-ray nuclear deexcitation lines; and (3) high-energy neutrons observed in space or by ground-based neutron monitors. The particles that escape into space consist of both electrons and ions, which often have compositions quite different than that of the ambient solar atmosphere. Flares thus present many diagnostics of the particle acceleration mechanism(s), the identification of which is the ultimate goal of flare research. Moreover, flares in fact offer the only opportunity in astrophysics to study the simultaneous energization of both electrons and ions. Hopefully, an understanding of flares with their wealth of diagnostic data will lead to a better understanding of particle acceleration at other sites in the Universe. It is now generally accepted that flares are roughly divided into two classes: impulsive and gradual. Gradual events are large, occur high in the corona, have long-duration soft and hard X-rays and gamma rays, are electron poor, are associated with Type II radio emission and coronal mass ejections (CMEs), and produce energetic ions with coronal abundance ratios. Impulsive events are more compact, occur lower in the corona, produce short-duration radiation, and exhibit dramatic abundance enhancements in the energetic ions. Their He-3/He-4 ratio is - 1, which is a huge increase over the coronal value of about 5 x 10(exp -4), and they also posses smaller but still significant enhancements of Ne, Mg, Si, and Fe relative to He-4, C, N, and O. Specifically, above about 1 MeV nucleon(exp -1), the ratio of Fe to O is about 8 times larger than in the corona or in gradual flares, while the ratio of Ne, Mg, and Si to O is about 3 times higher; He-4, C, N, and 0 are not enchanced with respect to each other. In addition to these elemental enhancements, Ne and Mg have isotopic enhancements as well. The general scenario that has emerged from these (and other) observations is that energetic particles in gradual events are accelerated by a CME-driven shock, while those particles in impulsive events are accelerated by another mechanism(s).

Miller, James A.↗
NASA NTRS1983

Magnetic field line reconnection experiments. V - Current disruptions and double layers

An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

Stenzel, R. L.↗
NASA NTRS1997

Predictive Modeling in Plasma Reactor and Process Design

Research continues toward the improvement and increased understanding of high-density plasma tools. Such reactor systems are lauded for their independent control of ion flux and energy enabling high etch rates with low ion damage and for their improved ion velocity anisotropy resulting from thin collisionless sheaths and low neutral pressures. Still, with the transition to 300 mm processing, achieving etch uniformity and high etch rates concurrently may be a formidable task for such large diameter wafers for which computational modeling can play an important role in successful reactor and process design. The inductively coupled plasma (ICP) reactor is the focus of the present investigation. The present work attempts to understand the fundamental physical phenomena of such systems through computational modeling. Simulations will be presented using both computational fluid dynamics (CFD) techniques and the direct simulation Monte Carlo (DSMC) method for argon and chlorine discharges. ICP reactors generally operate at pressures on the order of 1 to 10 mTorr. At such low pressures, rarefaction can be significant to the degree that the constitutive relations used in typical CFD techniques become invalid and a particle simulation must be employed. This work will assess the extent to which CFD can be applied and evaluate the degree to which accuracy is lost in prediction of the phenomenon of interest; i.e., etch rate. If the CFD approach is found reasonably accurate and bench-marked with DSMC and experimental results, it has the potential to serve as a design tool due to the rapid time relative to DSMC. The continuum CFD simulation solves the governing equations for plasma flow using a finite difference technique with an implicit Gauss-Seidel Line Relaxation method for time marching toward a converged solution. The equation set consists of mass conservation for each species, separate energy equations for the electrons and heavy species, and momentum equations for the gas. The sheath is modeled by imposing the Bohm velocity to the ions near the walls. The DSMC method simulates each constituent of the gas as a separate species which would be analogous in CFD to employing separate species mass, momentum, and energy equations. All particles including electrons are moved and allowed to collide with one another with the stipulation that the electrons remain tied to the ions consistent with the concept of ambipolar diffusion. The velocities of the electrons are allowed to be modified during collisions and are not confined to a Maxwellian distribution. These benefits come at a price in terms of computational time and memory. The DSMC and CFD are made as consistent as possible by using similar chemistry and power deposition models. Although the comparison of CFD and DSMC is interesting, the main goal of this work is the increased understanding of high-density plasma flowfields that can then direct improvements in both techniques. This work is unique in the level of the physical models employed in both the DSMC and CFD for high-density plasma reactor applications. For example, the electrons are simulated in the present DSMC work which has not been done before for low temperature plasma processing problems. In the CFD approach, for the first time, the charged particle transport (discharge physics) has been self-consistently coupled to the gas flow and heat transfer.

Hash, D. B.↗
NASA NTRS2016

The Variable Crab Nebula: Evidence for a Connection Between GeV Flares and Hard X-ray Variations

In 2010, hard X-ray variations (Wilson-Hodge et al. 2011) and GeV flares (Tavani et al 2011, Abdo et al. 2011) from the Crab Nebula were discovered. Connections between these two phenomena were unclear, in part because the timescales were quite different, with yearly variations in hard X-rays and hourly to daily variations in the GeV flares. The hard X-ray flux from the Crab Nebula has again declined since 2014, much like it did in 2008-2010. During both hard X-ray decline periods, the Fermi LAT detected no GeV flares, suggesting that injection of particles from the GeV flares produces the much slower and weaker hard X-ray variations. The timescale for the particles emitting the GeV flares to lose enough energy to emit synchrotron photons in hard X-rays is consistent with the yearly variations observed in hard X-rays and with the expectation that the timescale for variations slowly increases with decreasing energy. This hypothesis also predicts even slower and weaker variations below 10 keV, consistent with the non-detection of counterparts to the GeV flares by Chandra (Weisskopf et al 2013). We will present a comparison of the observed hard X-ray variations and a simple model of the decay of particles from the GeV flares to test our hypothesis.

Variable Crab Nebula↗
NASA NTRS1972

The Martian atmosphere - Mariner 9 television experiment progress report.

Atmospheric phenomena appearing in the Mariner 9 television pictures are discussed in detail. The surface of the planet was heavily obscured by a global dust storm during the first month in orbit. Brightness data during this period can be fitted by a semi-infinite scattering and absorbing atmosphere model with a single-scattering albedo in the range 0.70-0.85. This low value suggests that the mean radius of the particles responsible for the obscuration was at least 10 microns. By the end of the second month, this dust storm had largely dissipated, leaving a residual optical depth of about 0.1. Much of the region north of 45 deg N was covered by variable clouds comprising the north polar hood.

Leovy, C. B.↗
NASA NTRS2002

Unified Instrumentation: Examining the Simultaneous Application of Advanced Measurement Techniques for Increased Wind Tunnel Testing Capability

A Unified Instrumentation Test examining the combined application of Pressure Sensitive Paint, Projection Moire Interferometry, Digital Particle Image Velocimetry, Doppler Global Velocimetry, and Acoustic Microphone Array has been conducted at the NASA Langley Research Center. The fundamental purposes of conducting the test were to: (a) identify and solve compatibility issues among the techniques that would inhibit their simultaneous application in a wind tunnel, and (b) demonstrate that simultaneous use of advanced instrumentation techniques is feasible for increasing tunnel efficiency and identifying control surface actuation / aerodynamic reaction phenomena. This paper provides summary descriptions of each measurement technique used during the Unified Instrumentation Test, their implementation for testing in a unified fashion, and example results identifying areas of instrument compatibility and incompatibility. Conclusions are drawn regarding the conditions under which the measurement techniques can be operated simultaneously on a non-interference basis. Finally, areas requiring improvement for successfully applying unified instrumentation in future wind tunnel tests are addressed.

Fleming, Gary A.↗
NASA NTRS2005

Simulation of Laser Cooling and Trapping in Engineering Applications

An advanced computer code is undergoing development for numerically simulating laser cooling and trapping of large numbers of atoms. The code is expected to be useful in practical engineering applications and to contribute to understanding of the roles that light, atomic collisions, background pressure, and numbers of particles play in experiments using laser-cooled and -trapped atoms. The code is based on semiclassical theories of the forces exerted on atoms by magnetic and optical fields. Whereas computer codes developed previously for the same purpose account for only a few physical mechanisms, this code incorporates many more physical mechanisms (including atomic collisions, sub-Doppler cooling mechanisms, Stark and Zeeman energy shifts, gravitation, and evanescent-wave phenomena) that affect laser-matter interactions and the cooling of atoms to submillikelvin temperatures. Moreover, whereas the prior codes can simulate the interactions of at most a few atoms with a resonant light field, the number of atoms that can be included in a simulation by the present code is limited only by computer memory. Hence, the present code represents more nearly completely the complex physics involved when using laser-cooled and -trapped atoms in engineering applications. Another advantage that the code incorporates is the possibility to analyze the interaction between cold atoms of different atomic number. Some properties that cold atoms of different atomic species have, like cross sections and the particular excited states they can occupy when interacting with each other and light fields, play important roles not yet completely understood in the new experiments that are under way in laboratories worldwide to form ultracold molecules. Other research efforts use cold atoms as holders of quantum information, and more recent developments in cavity quantum electrodynamics also use ultracold atoms to explore and expand new information-technology ideas. These experiments give a hint on the wide range of applications and technology developments that can be tackled using cold atoms and light fields. From more precise atomic clocks and gravity sensors to the development of quantum computers, there will be a need to completely understand the whole ensemble of physical mechanisms that play a role in the development of such technologies. The code also permits the study of the dynamic and steady-state operations of technologies that use cold atoms. The physical characteristics of lasers and fields can be time-controlled to give a realistic simulation of the processes involved such that the design process can determine the best control features to use. It is expected that with the features incorporated into the code it will become a tool for the useful application of ultracold atoms in engineering applications. Currently, the software is being used for the analysis and understanding of simple experiments using cold atoms, and for the design of a modular compact source of cold atoms to be used in future research and development projects. The results so far indicate that the code is a useful design instrument that shows good agreement with experimental measurements (see figure), and a Windows-based user-friendly interface is also under development.

Ramirez-Serrano, Jaime↗
NASA NTRS2023

Solar Activity Relations in Energetic Electron Events Measured By the MESSENGER Mission

Aims. We perform a statistical study of the relations between the properties of solar energetic electron (SEE) events measured by the MESSENGER mission from 2010 to 2015 and the parameters of the respective parent solar activity phenomena in order to identify the potential correlations between them. During the time of analysis, the MESSENGER heliocentric distance varied between 0.31 and 0.47 au. Methods. We used a published list of 61 SEE events measured by MESSENGER, which includes information on the near-relativistic electron peak intensities, the peak-intensity energy spectral indices, and the measured X-ray peak intensity of the flares related to the SEE events. Taking advantage of multi-viewpoint remote-sensing observations, we reconstructed, whenever possible, the associated coronal mass ejections (CMEs) and shock waves; and we determined the three-dimensional (3D) properties (location, speed, and width) of the CMEs and the maximum speed of the 3D CME-driven shocks in the corona. We used different methods (Spearman, Pearson, and a Bayesian approach, namely the Kelly method to linear regression) to estimate the correlation coefficients between the flare intensity, maximum speed at the apex of the CME-driven shock, CME speed at the apex, and CME width with the electron peak intensities and with the energy spectral indices. In this statistical study, we considered and addressed the limitations of the particle instrument on board MESSENGER (elevated background intensity level, anti-Sun pointing). Results. There is an asymmetry to the east in the range of connection angles (CAs) for which the SEE events present the highest peak intensities, where the CA is the longitudinal separation between the footpoint of the magnetic field connecting to the spacecraft and the flare location. Based on this asymmetry, we define a subsample of well-connected events as when −65° ≤ CA ≤ +33°. For the well-connected sample, we find moderate to strong correlations between the near-relativistic electron peak intensity and the 3D CME-driven shock maximum speed at the apex (Spearman: cc = 0.53 ± 0.05; Pearson: cc = 0.65 ± 0.04; Kelly: cc = 0.87 ± 0.20), the flare peak intensity (Spearman: cc = 0.63 ± 0.03; Pearson: cc = 0.59 ± 0.03; Kelly: cc = 0.74 ± 0.30), and the 3D CME speed at the apex (Spearman: cc = 0.50 ± 0.04; Pearson: cc = 0.46 ± 0.03; Kelly: cc = 0.60 ± 0.39). When including poorly connected events (full sample), the relations between the peak intensities and the solar-activity phenomena are blurred, showing lower correlation coefficients. Conclusions. Based on the comparison of the correlation coefficients presented in this study using near 0.4 au data, (1) both flare and shock-related processes may contribute to the acceleration of near relativistic electrons in large SEE events, in agreement with previous studies based on near 1 au data; and (2) the maximum speed of the CME-driven shock is a better parameter to investigate particle-acceleration-related mechanisms than the average CME speed, as suggested by the stronger correlation with the SEE peak intensities.

Sun↗
NASA NTRS1976

Research in space physics at the University of Iowa

Energetic particles in outer space and their relationship to electric, magnetic, and electromagnetic fields associated with the earth, sun, moon, and planets, and the interplanetary medium are investigated. Special attention was given to observations of earth and moon satellites and interplanetary spacecraft; phenomenological analysis and interpretation were emphasized. Data also cover ground based on radio astronomical and optical techniques and theoretical problems in plasma physics as revelant to solar planetary and interplanetary phenomena.

Vanallen, J. A.↗
NASA NTRSDate not supplied

Ionospheric Response to Electron Precipitation Driven by Whistler-Mode Chorus Waves Measured by Arase Satellite and Simulated by STET and SPEAH-RIT

The origin of pulsating auroras has long been an open question. Arase satellite observation reported the direct evidence that precipitated electrons in pulsating aurora are driven by whistler-mode chorus wave activity. Our study presents the theoretical analysis of this observational event based on SuperThermal Electron Transport (STET) code that simulates the highly dynamic environment of measured wave intensities and particle fluxes. Specifically, the STET code simulated results confirm the delicate loss-cone observation results of this mission and reveal the broader energy range of precipitated electron fluxes that were not measurable by Arase satellite. These highly dynamic precipitating electron fluxes were applied to a newly developed code, the Superthermal Proton, Electron and Atomic Hydrogen tRansport in the Ionosphere and Thermosphere (SPEAH-RIT), to simulate ionospheric response of this phenomena, in particular, the enhancement of electron density, plasma temperatures, and ionospheric electric conductance at the footprints of Arase satellite.

George V. Khazanov↗
NASA NTRS1981

Review of auroral particle precipitation

An attempt to establish the precipitation signal of an auroral arc based on data gathered by sounding rockets and satellites is presented. Rocket sounding is useful for altitudes up to a few thousand km, the S3-3 satellite from 4000-8000 km, and satellites in GEO for the equatorial plane. Inverted V structures have been observed down to a few km in width by rockets, and occur on open as well as closed field lines. Observations of bursts of field-aligned electrons, simultaneous ion and electron precipitation, counter-streaming electrons and conics have been interpreted as indicating ac phenomena. The S3-3 has recorded the presence of upward flowing ions, beams, and conics, downward flowing ions, and counter-streaming electrons in the 4000-8000 km region. Finally, plasma injections at synchronous orbit have been identified as the equatorial plane signature of any auroral substorm.

Arnoldy, R. L.↗
NASA NTRS2009

Electric Field Observations of Plasma Convection, Shear, Alfven Waves, and other Phenomena Observed on Sounding Rockets in the Cusp and Boundary Layer

On December 14,2002, a NASA Black Brant X sounding rocket was launched equatorward from Ny Alesund, Spitzbergen (79 N) into the dayside cusp and subsequently cut across the open/closed field line boundary, reaching an apogee of771 km. The launch occurred during Bz negative conditions with strong By negative that was changing during the flight. SuperDarn (CUTLASS) radar and subsequent model patterns reveal a strong westward/poleward convection, indicating that the rocket traversed a rotational reversal in the afternoon merging cell. The payload returned DC electric and magnetic fields, plasma waves, energetic particle, suprathermal electron and ion, and thermal plasma data. We provide an overview of the main observations and focus on the DC electric field results, comparing the measured E x B plasma drifts in detail with the CUTLASS radar observations of plasma drifts gathered simultaneously in the same volume. The in situ DC electric fields reveal steady poleward flows within the cusp with strong shears at the interface of the closed/open field lines and within the boundary layer. We use the observations to discuss ionospheric signatures of the open/closed character of the cusp/low latitude boundary layer as a function of the IMF. The electric field and plasma density data also reveal the presence of very strong plasma irregularities with a large range of scales (10 m to 10 km) that exist within the open field line cusp region yet disappear when the payload was equatorward of the cusp on closed field lines. These intense low frequency wave observations are consistent with strong scintillations observed on the ground at Ny Alesund during the flight. We present detailed wave characteristics and discuss them in terms of Alfven waves and static irregularities that pervade the cusp region at all altitudes.

Pfaff, R. F.↗
NASA NTRS1984

Computer simulation of surface and film processes

All the investigations which were performed employed in one way or another a computer simulation technique based on atomistic level considerations. In general, three types of simulation methods were used for modeling systems with discrete particles that interact via well defined potential functions: molecular dynamics (a general method for solving the classical equations of motion of a model system); Monte Carlo (the use of Markov chain ensemble averaging technique to model equilibrium properties of a system); and molecular statics (provides properties of a system at T = 0 K). The effects of three-body forces on the vibrational frequencies of triatomic cluster were investigated. The multilayer relaxation phenomena for low index planes of an fcc crystal was analyzed also as a function of the three-body interactions. Various surface properties for Si and SiC system were calculated. Results obtained from static simulation calculations for slip formation were presented. The more elaborate molecular dynamics calculations on the propagation of cracks in two-dimensional systems were outlined.

Tiller, W. A.↗
NASA NTRS2011

Detection and Correction of Step Discontinuities in Kepler Flux Time Series

PDC 8.0 includes an implementation of a new algorithm to detect and correct step discontinuities appearing in roughly one of every 20 stellar light curves during a given quarter. The majority of such discontinuities are believed to result from high-energy particles (either cosmic or solar in origin) striking the photometer and causing permanent local changes (typically -0.5%) in quantum efficiency, though a partial exponential recovery is often observed [1]. Since these features, dubbed sudden pixel sensitivity dropouts (SPSDs), are uncorrelated across targets they cannot be properly accounted for by the current detrending algorithm. PDC detrending is based on the assumption that features in flux time series are due either to intrinsic stellar phenomena or to systematic errors and that systematics will exhibit measurable correlations across targets. SPSD events violate these assumptions and their successful removal not only rectifies the flux values of affected targets, but demonstrably improves the overall performance of PDC detrending [1].

Kolodziejczak, J. J.↗