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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 1,315 records · Page 73

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NASA NTRS1995

Probing transmembrane mechanical coupling and cytomechanics using magnetic twisting cytometry

We recently developed a magnetic twisting cytometry technique that allows us to apply controlled mechanical stresses to specific cell surface receptors using ligand-coated ferromagnetic microbeads and to simultaneously measure the mechanical response in living cells. Using this technique, we have previously shown the following: (i) beta 1 integrin receptors mediate mechanical force transfer across the cell surface and to the cytoskeleton, whereas other transmembrane receptors (e.g., scavenger receptors) do not; (ii) cytoskeletal stiffness increases in direct proportion to the level of stress applied to integrins; and (iii) the slope of this linear stiffening response differs depending on the shape of the cell. We now show that different integrins (beta 1, alpha V beta 3, alpha V, alpha 5, alpha 2) and other transmembrane receptors (scavenger receptor, platelet endothelial cell adhesion molecule) differ in their ability to mediate force transfer across the cell surface. In addition, the linear stiffening behavior previously observed in endothelial cells was found to be shared by other cell types. Finally, we demonstrate that dynamic changes in cell shape that occur during both cell spreading and retraction are accompanied by coordinate changes in cytoskeletal stiffness. Taken together, these results suggest that the magnetic twisting cytometry technique may be a powerful and versatile tool for studies analyzing the molecular basis of transmembrane mechanical coupling to the cytoskeleton as well as dynamic relations between changes in cytoskeletal structure and alterations in cell form and function.

NASA Discipline Number 40-20↗

NASA NTRS1999

Dynamics of the Auroral Luminosity Boundary of the Polar Cap During Substorms

The area of the polar cap during substorms has been measured using images from the Polar Ultraviolet Imager (UVI) for different interplanetary magnetic field (IMF) conditions. Changes in the poleward boundary of auroral luminosity have been analyzed in relation to substorm phase and IMF orientation. Reconnection models of flux transport into the polar cap during the substorm growth phase, and loss from the polar cap during the expansion phase, provide a framework by which these UVI observations can be analyzed. By comparison of the observations with the model predictions we can determine to what extent these models accurately predict the polar cap dynamics, and also where anomalous behavior calls for a new understanding of the dynamics beyond what these models provide. It was found that the polar cap boundary near noon and midnight usually shifted down in latitude by 1-2 degrees and 3-4 degrees respectively, increasing the area of the polar cap during the substorm growth phase as predicted. However, this growth phase phenomenon also unexpectedly occurs independently of the IMF Bz component, as shown for a substorm on January 9, 1997. The polar cap area also increased due to motion of the dawn and dusk aurora to lower latitudes, although the latitudinal shifts were asymmetric, not always concurrent, and continued well into the substorm expansion phase. The polar cap area decreased immediately following the expansion phase due to the poleward motion of the aurora on the nightside, consistent with the model prediction. What is not explained by the models is that the poleward auroral boundary in the nightside region sometimes reached very high latitudes (greater than 80 degrees MLat) greatly decreasing the polar cap area, independent of the magnitude of the substorm.

Brittnacher, M. J.↗

NASA NTRS1982

A post-Voyager view of Saturn's environment

Major results obtained by Voyager spacecraft encounters in the vicinity of Saturn are discussed, noting that the hydrogen torus dominates the Saturn magnetosphere without directly participating in its dynamics, being neutral. The average sunward location of the magnetopause has been found to generally lie beyond the orbit of Titan, and is determined by the pressure balance between the solar wind and the planetary magnetic field. Energetic electrons were observed during Voyager 1 traversal of the Saturn magnetic tail down to the magnetopause, indicating that field lines in the tail lobe of the Saturn magnetosphere are closed. The detailed analysis of Voyager 1 and 2 encounters with Saturn will continue for another two years, exploring the dynamics of the magnetosphere itself and of its interaction with the rings, satellites, and ionosphere of the planet.

Krimigis, S. M.↗

NASA NTRS1994

Particle/fluid simulations of an eruptive flare: Identifying the field-aligned currents responsible for the hard x-rays

While magnetohydrodynamics (MHD) can provide a reasonable description of the overall magnetic reconnection that is believed to drive flares, additional, and often separate processes have to be envoked to in order to explain the electron acceleration that is responsible for many of the observed flare emissions. A new model that incorporates the dynamic coronal current sheets, the reconnection site, and possible electron acceleration processes is developed through the use of two-dimensional particle and modified two-fluid simulations. The specific example of an eruptive flare driven by the coalescence of flux tubes supported by prescribed photospheric current elements is evaluated. It is shown that the electrons and ions have differential trajectories through the coronal current sheet which leads to the development of additonal plasma currents that flow around the surface of the current sheet. These surface currents are explicitly neglected in MHD but they are vital to the flare dynamics because they divert current from the coronal current sheet into the chromosphere, producing an effective resistivity that aids the development of fast reconnection. Because the surface currents are in the plane of the magnetic field, electrons in them experience strong acceleration and can account for the observed hard X-ray emissions. Model predictions are compared with observed time profiles of hard X-ray emissions and Doppler shifts seen in soft X-ray line emissions and are able to account for such features as (1) the asymmetry in the rise and decay time of the hard X-rays, (2) the apparent delay between the largest Doppler shifts and the hard X-ray peak, and (3) the relatively low intensity of the blue-shifted component. The use of particle and fluid simulations is important because it provides different, but complementary treatments of the electron acceleration, the global magnetic morphology, and the flare current system.

Winglee, R. M.↗

NASA NTRS2023

Deriving Large Coronal Magnetic Loop Parameters Using LOFAR J Burst Observations

Large coronal loops around one solar radius in altitude are an important connection between the solar wind and the low solar corona. However, their plasma properties are ill-defined, as standard X-ray and UV techniques are not suited to these low-density environments. Diagnostics from type J solar radio bursts at frequencies above 10 MHz are ideally suited to understand these coronal loops. Despite this, J-bursts are less frequently studied than their type III cousins, in part because the curvature of the coronal loop makes them unsuited for using standard coronal density models. We used LOw-Frequency-ARray (LOFAR) and Parker Solar Probe (PSP) solar radio dynamic spectrum to identify 27 type III bursts and 27 J-bursts during a solar radio noise storm observed on 10 April 2019. We found that their exciter velocities were similar, implying a common acceleration region that injects electrons along open and closed magnetic structures. We describe a novel technique to estimate the density model in coronal loops from J-burst dynamic spectra, finding typical loop apex altitudes around 1.3 solar radius. At this altitude, the average scale heights were 0.36 solar radius, the average temperature was around 1 MK, the average pressure was 0.7mdyn cm -2 , and the average minimum magnetic field strength was 0.13 G. We discuss how these parameters compare with much smaller coronal loops.

Jinge Zhang↗

NASA NTRS1997

Exterior and Interior Polar Cusps: Observations from Hawkeye

Hawkeye plasma, magnetic field, and plasma wave instruments directly sampled the throat of the northern polar cusp as the orientation of the Interplanetary Magnetic Field (IMF) changed from southward to northward on July 3, 1974. Two distinct regions in the polar cusp were identified based on magnetic field, plasma flow and magnetic and electric noise: the interior and exterior cusps. The observations show highly variable flows in the exterior portion of the cusp and constantly strong dawn-dusk flows in the interior portion during periods of strong IMF By component. Results of a minimum variance analysis of the magnetic field at each cusp interface crossing provides evidence that the magnetopause surface normal deviated highly from empirical models. During intervals of relatively steady solar wind dynamic pressure, the motion of the cusp relative to the slow moving spacecraft was modulated by the varying IMF clock angle as observed by IMP 8 in the upstream solar wind. The motion did not show a correlation with internal processes monitored by the A E index. We propose that observed plasma flow patterns and cusp motion are results of reconnection between the IMF and the magnetospheric magnetic field. Flow velocity observed in the interior cusp is consistent with stress balance for a reconnection process. This unique interval provides an opportunity for detailed studies of the plasma, magnetic field, and plasma wave properties in both the exterior and interior cusp.

Chen, S.-H.↗

NASA NTRS2017

Global Energetics of Solar Flares. V. Energy Closure in Flares and Coronal Mass Ejections

In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our findings are: (1) The sum of the mean nonthermal energy of flare-accelerated particles (E(sub nt)), the energy of direct heating (E(sub dir)), and the energy in coronal mass ejections (E(sub CME)), which are the primary energy dissipation processes in a flare, is found to have a ratio of (E(sub nt) + E(sub dir) + E(sub CME))/E(sub mag) = 0.87±0.18, compared with the dissipated magnetic free energy E(sub mag), which confirms energy closure within the measurement uncertainties and corroborates the magnetic origin of flares and CMEs; (2) The energy partition of the dissipated magnetic free energy is: 0.51±0.17 in nonthermal energy of ≥ 6 keV electrons, 0.17± 0.17 in nonthermal ≥ 1 MeV ions, 0.07 ± 0.14 in CMEs, and 0.07 ± 0.17 in direct heating; (3) The thermal energy is almost always less than the nonthermal energy, which is consistent with the thick-target model; (4) The bolometric luminosity in white-light flares is comparable with the thermal energy in soft X-rays (SXR); (5) Solar Energetic Particle (SEP) events carry a fraction ≈ 0.03 of the CME energy, which is consistent with CME-driven shock acceleration; and (6) The warm-target model predicts a lower limit of the low-energy cutoff at e(sub c) ≈ 6 keV, based on the mean differential emission measure (DEM) peak temperature of T(sub e) = 8.6 MK during flares. This work represents the first statistical study that establishes energy closure in solar flare/CME events.

Solar activity↗

NASA NTRS2017

Global Energetics of Solar Flares. V. Energy Closure in Flares and Coronal Mass Ejections

In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our findings are: (1) The sum of the mean nonthermal energy of flare-accelerated particles (E(sub nt)), the energy of direct heating (E(sub dir)), and the energy in coronal mass ejections (E(sub CME)), which are the primary energy dissipation processes in a flare, is found to have a ratio of (E(sub nt)+E(sub dir)+E(sub CME))/E(sub mag) = 0.87±0.18, compared with the dissipated magnetic free energy E(sub mag), which confirms energy closure within the measurement uncertainties and corroborates the magnetic origin of flares and CMEs; (2) The energy partition of the dissipated magnetic free energy is: 0.51±0.17 in nonthermal energy of ≥ 6 keV electrons, 0.17± 0.17 in nonthermal ≥ 1 MeV ions, 0.07 ± 0.14 in CMEs, and 0.07 ± 0.17 in direct heating; (3) The thermal energy is almost always less than the nonthermal energy, which is consistent with the thick-target model; (4) The bolometric luminosity in white-light flares is comparable with the thermal energy in soft X-rays (SXR); (5) Solar Energetic Particle (SEP) events carry a fraction ≈ 0.03 of the CME energy, which is consistent with CME-driven shock acceleration; and (6) The warm-target model predicts a lower limit of the low-energy cutoff at ec ≈ 6 keV, based on the mean differential emission measure (DEM) peak temperature of T(sub e) = 8.6 MK during flares. This work represents the first statistical study that establishes energy closure in solar flare/CME events.

Solar activity↗

NASA NTRS2017

Global Energetics of Solar Flares and CMEs: V. Energy Closure

In this study we synthesize the results of four previous studies on the global energetics of solar flares and associated coronal mass ejections (CMEs), which include magnetic, thermal, nonthermal, and CME energies in 399 solar M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission. Our findings are: (1) The sum of the mean nonthermal energy of flare-accelerated particles (E(sub nt)), the energy of direct heating (E(sub dir)), and the energy in coronal mass ejections (E(sub CME)), which are the primary energy dissipation processes in a flare, is found to have a ratio of (E(sub nt)+E(sub dir)+E(sub CME))/E(sub mag) = 0.87±0.18, compared with the dissipated magnetic free energy E(sub mag), which confirms energy closure within the measurement uncertainties and corroborates the magnetic origin of flares and CMEs; (2) The energy partition of the dissipated magnetic free energy is: 0.51±0.17 in nonthermal energy of ≥ 6 keV electrons, 0.17± 0.17 in nonthermal ≥ 1 MeV ions, 0.07 ± 0.14 in CMEs, and 0.07 ± 0.17 in direct heating; (3) The thermal energy is almost always less than the nonthermal energy, which is consistent with the thick-target model; (4) The bolometric luminosity in white-light flares is comparable with the thermal energy in soft X-rays (SXR); (5) Solar Energetic Particle (SEP) events carry a fraction ≈ 0.03 of the CME energy, which is consistent with CME-driven shock acceleration; and (6) The warm-target model predicts a lower limit of the low-energy cutoff at e(sub c) ≈ 6 keV, based on the mean differential emission measure (DEM) peak temperature of T(sub e) = 8.6 MK during flares. This work represents the first statistical study that establishes energy closure in solar flare/CME events.

Solar activity↗

NASA NTRS1985

Fine structure and dynamics of the Harang discontinuity - An event study

Two rockets were launched simultaneously from the Andoya Rocket Range in northern Norway into and through a Harang discontinuity region during a small isolated substorm. Each was equipped with an array of instruments for monitoring ionospheric electric fields and auroral particles. Different sized rockets allowed both to traverse a range of 300 km while introducing altitude separations of up to 440 km, and separations between the feet of the magnetic field lines intersecting the payloads of up to 100 km. The data sets, coupled with multi-station ground-based observations, provide information on the structure and dynamics of the Harang discontinuity region. Two boundaries were encountered. The first electric field reversal was observed simultaneously by both payloads in a region of weak precipitation, while the second reversal was associated with an intense auroral band. Since an unambiguous interpretation of these data is not possible, two alternative scenarios are presented. In one the discontinuity becomes realigned during the flight following a decay in the activity. The second involves a triple cell convection system, possibly the result of an eddy in the flow.

Egeland, A.↗

NASA NTRS2020

How Magnetically Conjugate Atmospheres and the Magnetosphere Participate in the Formation of Low‐Energy Electron Precipitation in the Region of Diffuse Aurora

The electron precipitation in the region of the diffuse aurora should be considered as a two‐step process (Khazanov et al., 2017, https://doi.org/10.1002/2016GL072063). The first one is the interaction of plasma sheet electrons with electrostatic electron cyclotron and/or whistler waves, moving those electrons into the loss cone to precipitate in both magnetically conjugate atmospheres. The second step is the interaction of these electrons with the ionosphere and atmosphere via their elastic and nonelastic collisions and reflection (backscatter) of degraded electrons back to magnetosphere and conjugate ionospheres. This paper presents the results of a newly developed scenario of non steady‐state electron precipitation dynamics that accounts for magnetosphere‐ionosphere‐atmosphere energy interplay over the entire energy range of the plasma sheet electron population and their affiliated secondary electrons. It also studies how both magnetically conjugate auroral regions work together with the magnetosphere in the formation of electron precipitation in the region of the diffuse aurora with the energy range coverage from 1 eV up to 10 keV.

George V Khazanov↗

NASA NTRS1983

Magnetic field reconnection at the magnetopause: An overview

The basic qualitative and quantitative aspects of reconnection in its magnetopause setting are summarized. First, the basic morphological and dynamic features of asymmetric reconnection are examined with emphasis on the important role played by the rotational discontinuity in these geometries. Second, the structure and other properties of rotational discontinuities are discussed. Third, the manner in which individual particles are energized or de-energized during their interaction with current layers in general, and rotational discontinuities in particular, is examined. Finally, the question of nonsteady, localized reconnection and its relation to flux transfer events is discussed and a qualitative model is proposed to describe these phenomena.

Sonnerup, B. U. O.↗

NASA NTRS1984

Magnetic field reconnection at the magnetopause - An overview

Sonnerup, B. U. O.↗

NASA NTRS1974

Interplanetary stream magnetism: Kinematic effects

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.↗

NASA NTRS1978

Acceleration and heating of the solar wind

Some of the competing theories of solar wind acceleration and heating are reviewed, and the observations that are required to distinguish among them are discussed. In most cases what is required is measurement of plasma velocity and temperature and magnetic field, as near the sun as possible and certainly inside 20 solar radii; another critical aspect of this question is determining whether a turbulent envelope exists in this inner region, and if so, defining its properties. Plasma and magnetic observations from the proposed Solar Probe mission would thus yield a quantum jump in our understanding of the dynamics of the solar wind.

Barnes, A.↗

NASA NTRS1983

Magnetic fields and activity of the sun and stars - An overview

Recent work on the observation and theory of solar and stellar magnetic field activity and its relation to stellar activity is reviewed, emphasizing those aspects relevant to the problem of activity of red dwarf stars. New observational facts relevant to understanding the root cause of stellar surface activity are summarized and theoretical questions concerning the underlying physical basis for the observed correlations between stellar activity, rotation, and magnetic fields are addressed. These include dyanamo theory and the rotation-activity connection as well as flux tube dynamics and plasma heating.

Rosner, R.↗

NASA NTRS1984

Science with the solar optical telescope

The Solar Optical Telescope (SOT) is designed to provide the solar physics community with the data necessary for solving several fundamental problems in the energetics and dynamics of the solar atmosphere. Among these problems are questions on the origin and evolution of the sun's magnetic field, heating of the outer solar atmosphere, and sources of the solar wind in the lower lying regions of the outer atmosphere. The SOT will be built under the management of NASA's Goddard Space Flight Center, with science instruments provided by teams led by Principal Investigators. The telescope will be built by the Perkin-Elmer Corporation, and the science instruments selected for the first flight will be provided by the Lockheed Palo Alto Research Laboratory (LPARL) and the California Institute of Technology, with actual construction of a combined science instrument taking place at the LPARL. The SOT has a 1.3-meter-diameter primary mirror that will be capable of achieving diffraction-limited viewing in the visible of 0.1 arc-second. This dimension is less than a hydrodynamic scale-height or a mean-free-path of a continuum photon in the solar atmosphere. Image stability will be achieved by a control system in the telescope, which moves both the primary and tertiary mirrors in tandem, and will be further enhanced by a correlation tracker in the combined science instrument. The SOT Facility is currently scheduled for its first flight on Spacelab at the beginning of the 1990's.

Jordan, S. D.↗

NASA NTRS1989

Magnets promise productivity

The use of advanced magnetic suspension and balance systems (MSBS) in wind tunnels is examined. The advantages of MSBS are discussed, including accurate dynamic stability and free manipulation of the model aircraft allowing the free-flying model to respond dynamically to aerodynamic forces. Examples of wind tunnel tests employing MSBS are presented, including tests of a hypersonics parasol wing configuration and the simulation of the ejection of the crew-escape module from an aircraft.

Lawing, Pierce L.↗