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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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NASA NTRS1978

Bursty channel errors and the Viterbi decoder

Recent applications have developed for spread spectrum communications, hardware data transfer, high rate digital systems, etc. that use channels for which errors tend to occur in short bursts in addition to those at random, i.e., compound channels. Viterbi decoding algorithms are generally very good for random error channels but are not as efficient for burst errors or for compound channels. This paper presents the results of a computer simulation study of the performance of various Viterbi decoders when receiving data corrupted with burst and random errors on the same channel. Simulations were performed using hard-decision CPSK.

Ingels, F.↗
NASA NTRS2000

Observations and Simulations of the M-I Coupling of Bursty Convection

The aim of the project is to establish how much of the magnetotail's total potential is due to flow bursts and how much of this potential maps to the ionosphere. In order to quantify these contributions, we need to develop a reliable method to measure the total cross-polar cap potential and the total reconnection rate across the entire polar cap boundary. This was the goal achieved in the first year of the grant. In the following section, we describe in more detail the activities leading to this goal.

Sanchez, Ennio R.↗
NASA NTRS2001

Observations and Simulations of the M-I Coupling of Bursty Convection

The ultimate aim of the project is to establish how much of the magnetotail's total potential is due to flow bursts and how much of this potential maps to the ionosphere. In order to quantify these contributions, we further developed a method to measure the total cross-polar cap potential and the total reconnection rate across the entire polar cap boundary. Then we applied the method to different solar wind-magnetosphere-ionosphere conditions that included substorm periods, storms, and steady magnetospheric convection (SMCs, also known as convection bays) periods. In the following section, we describe in more detail the activities during the second year of this grant.

Sanchez, Ennio R.↗
NASA NTRS2007

"Bursty" Reconnection Following Solar Eruptions: MHD Simulations and Comparison with Observations

Posteruptive arcades are frequently seen in the aftermath of coronal mass ejections (CMEs). The formation of these loops at successively higher altitudes, coupled with the classic "two-ribbon" flare seen in H-alpha, are interpreted as reconnection of the coronal magnetic field that has been dragged outward by the CME. White-light observations of "rays," which have been interpreted as being coincident with the current sheet at the reconnection site underneath the erupting CME, also provide evidence for its occurrence. "Blobs" occasionally seen within these rays suggest an even richer level of structure. In this report, we present numerical simulations that reproduce both the observed rays and the formation and evolution of the blobs. We compare their properties with SOHO/LASCO observations of similar structures, and relate their formation to standard theories of reconnection,

Riley, Pete↗
NASA NTRS2011

Bursty Precipitation Driven by Chorus Waves

The electron precipitation bursts have been shown to be a major sink for the radiation belt relativistic electrons. As underlying mechanism of such bursts, we propose particle scattering into the loss cone due to nonlinear resonance interaction between electrons and chorus. Stochastic heating due to the coupling leads to diffusion in pitch angle, and the rate of diffusion would be sufficient to account for the emptying of the Earth's radiation belt over the time of the main phase of geomagnetic storms. The results obtained in the present paper account for a strong energy dependence in the electron precipitation event and the correlation between the energization and loss processes on macroscopic timescales, which is primarily attributed to the cooperative effects of the coupling. This mechanism of chorus scattering should produce pitch angle distributions that are energy-dependent and butterfly-shaped. The calculated timescales and the total energy input to the atmosphere from precipitating relativistic electrons are in reasonable agreement with experimental data.

Khazanov, G. V.↗
NASA NTRS2011

Examination of Bursty Electromagnetic Waves Observed During Intervals of Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic waves in association with magnetic reconnection in the turbulent magnetosheath. These structured, broadband bursts occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic waves and quantify their proximity to X- and O-nulls.

Adrian, Mark L.↗
NASA NTRS2011

Bursty, Broadband Electromagnetic Waves Associated with Thin Current Layers and Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed at local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X- and O-nulls, as well as their correlation to the amount of magnetic energy converted by the process of magnetic reconnection.

Adrian, M. L.↗
NASA NTRS2012

Bursty, Broadband Electromagnetic Waves Associated with Three-Dimensional Nulls Observed in Turbulent Magnetosheath Reconnection

We investigate observations of intense bursts of electromagnetic wave energy in association with the thin current layers of turbulent magnetosheath reconnection. These observed emissions - typically detected in the layers immediately outside of the current layer proper - form two distinct types: (i) broadband emissions that extend continuously to lOs of Hertz; and (ii) structured bursts of emitted energy that occur above 80-Hz, often displaying features reminiscent of absorption bands and are observed near the local minima in the magnetic field. We present detailed analyses of these intense bursts of electromagnetic energy and quantify their proximity to X-IO-nulls and magnetic spine connected null pairs, as well as their correlation - if any - to the amount of magnetic energy converted by the process of magnetic reconnection.

Adrian, Mark L.↗
NASA NTRS2012

Interpretation of Vector Electric Field Measurements of Bursty Langmuir Waves in the Cusp

An analysis of auroral Langmuir waves in the cusp observed by two high-frequency electric field instruments on the TRICE high-flyer sounding rocket shows many examples of Langmuir wave bursts modulated at approximately 10 kHz. Previous studies have explained these and similar observations as the result of beating between waves with very close frequencies near the Langmuir cutoff, resulting from either wave-wave interactions or independent linear excitations. The unique three-dimensional (3-D) data set provided by the NASA Goddard Space Flight Center TAEFWD instrument shows that up to 25% of waveforms selected from the most intense bursts exhibit anisotropic modulations, i.e., the beat nulls and peaks are not aligned in time across the three perpendicular electric field components. Modulations of this type arise when superposed wave normal modes possess differing polarizations, and simulations using wave modes calculated with the J-WHAMP numerical dispersion code show (1) that waves with differing polarizations can exist in conditions like those observed by TRICE-High and (2) that superpositions of such waves can produce anisotropic modulation. Fourier analysis of the 3-D waveform data suggests that both linear and elliptically polarized waves are present near the Langmuir cutoff at these times. These observations illustrate how 3-D measurements can give valuable insight into the nature of wave interactions in the auroral plasma environment.

Dombrowski, M. P.↗