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At least 847 records · Page 47

The radial dependences of the interplanetary magnetic field between 1 and 5 AU Pioneer 10

Pioneer 10 vector helium magnetometer data acquired in 1972-1973 during Bartels solar rotations 1896-1918 are used to investigate the radial dependences of the distant interplanetary magnetic field (IMF) between 1 and 5 AU. Least-square fits were determined for the radial dependences of the averages of the magnitudes of IMF components and total field and plane projections, and radial fits were prepared for the standard deviations of these variables over the solar rotation, one day, and three-hour intervals. The variation of the weighted averages of the radial component of the field with respect to the heliocentric distance, the variation of the tangential component of the field, and the characteristics of a subset corresponding to a relatively low average solar wind velocity are reported.

Rosenberg, R. L.↗

A fundamental magnetosphere-ionosphere coupling mode involving field-aligned currents as deduced from DE-2 observations

From the magnetic and electric field observations on the DE-2 satellite it is deduced that the perturbation magnetic field and the electric field in the field-aligned current regions are, as a rule, orthogonal to each other and are highly correlated. This deduction is equivalent to the statement that the Poynting vector calculated from these magnetic and electric field components is equal to the ionospheric energy dissipation and that the height-integrated Hall current is divergence free. The state described is interpreted as a frequently prevailing mode of the magnetosphere-ionosphere coupling involving field-aligned currents.

Sugiura, M.↗

Role of inductive electric fields in substorm development

A study discussing and investigating the role of inductive electric fields in substorm development is presented. It is common to use the scalar potential phi to calculate the electrostatic field E(sup ES)-(inverted Delta)(phi). However, vector potential A has not been extensively used to analyze results by the relation for the inductive electric field E(sup IND)-delta A/delta t. Because of the weak dependence in distance (1/r) these potentials show the effect of distant sources, unlike MHD (Magnetohydrodynamic) theory which is strictly local. The two can be separated by the choice of the Coulomb (transverse) gauge. It is proper to consider that the plasma polarizes to counteract the activation of the inductive electric field; this is a matter of cause and effect. However, such polarization produces a curl free electrostatic field and thus cannot alter the electromotive force due to induction. This idea has some interesting consequences for plasma physics, including violations of MHD theory, creation of the substorm current diversion, and a fresh look at dayside merging via plasma transfer events.

Heikkila, Walter J.↗

Report of the panel on geopotential fields: Magnetic field, section 9

The objective of the NASA Geodynamics program for magnetic field measurements is to study the physical state, processes and evolution of the Earth and its environment via interpretation of measurements of the near Earth magnetic field in conjunction with other geophysical data. The fields measured derive from sources in the core, the lithosphere, the ionosphere, and the magnetosphere. Panel recommendations include initiation of multi-decade long continuous scalar and vector measurements of the Earth's magnetic field by launching a five year satellite mission to measure the field to about 1 nT accuracy, improvement of our resolution of the lithographic component of the field by developing a low altitude satellite mission, and support of theoretical studies and continuing analysis of data to better understand the source physics and improve the modeling capabilities for different source regions.

Achache, Jose J.↗

Micromechanics of Composite Materials Governed by Vector Constitutive Laws

The high-fidelity generalized method of cells micromechanics theory has been extended for the prediction of the effective property tensor and the corresponding local field distributions for composites whose constituents are governed by vector constitutive laws. As shown, the shear analogy, which can predict effective transverse properties, is not valid in the general three-dimensional case. Consequently, a general derivation is presented that is applicable to both continuously and discontinuously reinforced composites with arbitrary vector constitutive laws and periodic microstructures. Results are given for thermal and electric problems, effective properties and local field distributions, ordered and random microstructures, as well as complex geometries including woven composites. Comparisons of the theory's predictions are made to test data, numerical analysis, and classical expressions from the literature. Further, classical methods cannot provide the local field distributions in the composite, and it is demonstrated that, as the percolation threshold is approached, their predictions are increasingly unreliable. XXXX It has been observed that the bonding between the fibers and matrix in composite materials can be imperfect. In the context of thermal conductivity, such imperfect interfaces have been investigated in micromechanical models by Dunn and Taya (1993), Duan and Karihaloo (2007), Nan et al. (1997) and Hashin (2001). The present HFGMC micromechanical method, derived for perfectly bonded composite materials governed by vector constitutive laws, can be easily generalized to include the effects of weak bonding between the constituents. Such generalizations, in the context of the mechanical micromechanics problem, involve introduction of a traction-separation law at the fiber/matrix interface and have been presented by Aboudi (1987), Bednarcyk and Arnold (2002), Bednarcyk et al. (2004) and Aboudi et al. (2013) and will be addressed in the future.

micromechanics↗

Electromagnetic instabilities and gyrophase-bunched particles

The linear theory of electromagnetic instabilities at propagation parallel or antiparallel to a uniform magnetic field B(0) is used to calculate the relative phase angle between the fluctuating velocity vector of the jth component and the fluctuating magnetic field. A criterion that determines when this phase relationship leads to observable gyrophase bunching during the linear growth phase of an instability is also derived. The theory is applied to bunching of ion components by ion beam instabilities. Among the electromagnetic cool ion beam instabilities, it is found that the right-hand resonant mode is most likely to cause observable gyrophase bunching of an ion beam during linear growth.

Gary, S. P.↗

Analysis of magnetic fields using variational principles and CELAS2 elements

Prospective techniques for analyzing magnetic fields using NASTRAN are reviewed. A variational principle utilizing a vector potential function is presented which has as its Euler equations, the required field equations and boundary conditions for static magnetic fields including current sources. The need for an addition to this variational principle of a constraint condition is discussed. Some results using the Lagrange multiplier method to apply the constraint and CELAS2 elements to simulate the matrices are given. Practical considerations of using large numbers of CELAS2 elements are discussed.

Frye, J. W.↗

Laser diagnostics for microgravity droplet studies

An instrument has been designed, built, and tested for performing laser diagnostic measurements of droplet combustion in low-gravity-flight aircraft. Nonintrusive measurements are of particular importance for droplet combustion (the simplest example of non-premixed combustion) and transport in microgravity environments, where physical contact would introduce an unacceptable level of perturbations. The resolution of these diagnostics can also isolate transport to length scales much smaller than the droplet diameter. These techniques can be configured to instantaneously map an entire flow field in two and three dimensions, providing either qualitative or quantitative information on the distribution of a desired scalar or vector quantity. Detailing the gas-phase flow field and position of the flame front can be achieved using planar laser-induced fluorescence (PLIF) of OH or another flame front marker. An alternative approach is to obtain LIF from a diagnostic seed included in the liquid phase fuel; it would be consumed at the flame front. The main advantage to this approach is that it is easier to choose the wavelength of the molecular absorption which coincides with convenient laser wavelengths rather than finding lasers which can be configured to access OH. Our present method uses a nitrogen-pumped dye laser tuned to a sodium absorption and addition of small concentrations of NaCl to the fuel. Particle image velocimetry (PIV) is a laser-based technique which has recently had its practicality greatly enhanced by the development of high-resolution CCD cameras and the increase in speed and capacity of computer systems. With this technique, a seeded flow is illuminated with a double-pulsed laser sheet to generate a double exposure image on a film or CCD camera. Computer analysis of the image is used to determine the particle velocity vectors and, thus, the gas velocity within the plane of the laser sheet. Our current experiment uses PIV for measuring relative droplet gas-phase velocities in a parabolic flight environment. The results show successful application of PLIF relative to luminosity and radical emission near 308 nm. PIV results are less successful due to gas thermal expansion deflecting the seed particles away from the measurement volume. PIV is applicable for measurements in the absence of combustion.

Winter, Michael↗

Dual technique magnetometer experiment for the Cassini Orbiter spacecraft

The dual technique magnetometer to fly on the Cassini Saturn Orbiter Spacecraft is described. The instrument combines two separate techniques of measuring the magnetic field in space using both fluxgate and vector helium devices. In addition, the instrument can be operated in a special scalar mode which is to be used near the planet for highly accurate determination of the interior field of the planet. As well as the planetary field, the instrument will make large contributions to the scientific measurements of the planetary magnetosphere, the highly electrically conducting region of space surrounding Saturn permeated by the Saturnian field, the interaction of Saturn and the interplanetary medium and the interaction of Titan with its space environment.

Southwood, D. J.↗

Wind measurements for non-uniform wind fields from spaceborne scatterometers

Radar backscattering coefficient measurements by spaceborne scatterometers are presently simulated for the case of nonuniform wind fields, by means of a detailed numerical integration of the radar equation. The winds thus estimated are then compared with a nominal field which is defined as the average wind vector over the wind cell. The simulation results obtained for the NASA scatterometer are presented for cases of random wind fields whose spectra are consistent with the Seasat scatterometer sea surface wind spectrum. When the nonuniformity is small, system noise dominates the wind error; wind error degradation is therefore small for both perfect and imperfect coregistration cases. When it is relatively large, however, the wind error degradation persistently increases for both perfect and imperfect coregistrations.

Chi, Chong-Yung↗

Structure of turbulence in the presence of uniform shear

The structure of the vorticity field in homogeneous turbulent shear flow is analyzed using a database generated by direct numerical solution of the unsteady Navier-Stokes equations with up to 128x128x128 grid points. For two Reynolds numbers, the probability distribution of the inclination angle of the vorticity vectors, two-point correlations of the velocity and vorticity fields, and the instantaneous vorticity vectors and vortex lines in three-dimensional space were examined. It is shown that homogeneous turbulent shear flow contains a large number of horseshoe vortices. These vortices are most often found in planes inclined at 45 deg to the flow direction and are formed from the roll-up of sheets of transverse vorticity. These findings and similar results obtained in turbulent channel flow, lead to the conclusion that hairpin vortices are the characteristic vortical structures in all turbulent shear flows.

Moin, P.↗

Scalar Atomic Defect-Based Solid-State Self-calibrating Magnetometer (3SM) for Space Plasma Analysis

The Earth’s magnetosphere is a system of multiple, co-located particle populations interacting via plasma waves. Things to understand are driving processes, radiation belt and ring current issues, auroral physics, internal plasma processes, and magnetosphere-ionosphere mapping issues. These plasma-physics processes enable the Earth’s magnetosphere to evolve in response to temporal changes in the solar wind and they underlie the phenomena of space weather, which impacts spacecraft systems, astronauts, radio communications, and ground based electric-power grids. The objective of 3SM is to measure magnetic field strength and to calibrate the Vector Magnetometer (VM) device to maintain absolute accuracy during a mission. The 3SM features make the instrument preferably suited not only for the traditional role of scalar magnetometers as absolute references for the calibration of the on-board vector instruments, but also for extended operational capacities, such as higher frequency scalar measurements (of potential interest for magnetosphere studies for the low frequency part of the spectrum) or autonomous scalar / vector operations. Diamond has been the solid-state platform of choice for quantum device technologies for some time, however, it suffers from difficulties such as scalability, integration, and cost. While the diamond platform is very useful for quantum technologies, further development is needed to make it viable. The material platform of choice for NASA Glenn’s Quantum Sensing And Spin Physics (Q-SASP) is silicon carbide (SiC). This is due to the much higher industry development of the SiC material platform for high-power and high-temperature electronics. It leverages both the decades-long SiC development expertise and infrastructure at NASA Glenn and its growing capabilities in quantum metrology. To make SiC devices usable for quantum technologies such as quantum sources, a much deeper understanding of defects is needed. Q-SASP is developing quantum metrology capabilities to evaluate the energy structure, defect formation energy, band structure augmentation, generation/recombination rates, and limits of dipole-dipole coupling in non-metal implanted SiC devices. This can be achieved by analysis of zero-field splitting, low-field resonance, and singlet-triplet mixing through various forms of Electrically Detectable Magnetic Resonance (EDMR) and Near-Zero Field Magnetic Resonance (NZFMR) spectroscopy. This work will discuss recent system developments, device developments, computational modeling, and spectroscopy results and analysis of defects created by non-metal implantations in SiC devices. The defect formation energies of V Si ,V C , V C V Si , N C V Si , N Si , N C in 4H-SiC are previously reported values in other research [2]-[3]. The defect formation energies of PSi and PC were calculated in GPAW [fig 1A]. The basic underlying mechanism of the zero-field phenomenon is the mixing of singlet and triplet states [4]-[5]. In most spin-dependent transport, two electron spins are involved, and thus one must consider each of their interactions with the field. We investigated the electronic and magnetic properties of 4H-SiC and 6H-SiC. The defect formation energy helps us determine what types of defects we are observing in the SiC EDMR experiment. They have very low formation energy (it is negative). The phosphorus substitution in 4H-SiC is a very stable defect. The band diagrams provide us with vital information about how the electronic properties of SiC (such as band gap) change as we add non-metal defects. The zero-field splitting parameters allow us to study the inflection point in the NZFMR [fig 1B]. We clearly observed zero-field splitting. We also noted that the zero-field splitting remained constant with changing bias. We aspect it zero-field splitting to remain constant while the hyperfine and exchange interaction perturbations shift under the influence of an external magnetic field. This is the essence of quantum magnetometry and self-calibration.

space plasma↗

Circular Data Images for Directional Data

Directional data includes vectors, points on a unit sphere, axis orientation, angular direction, and circular or periodic data. The theoretical statistics for circular data (random points on a unit circle) or spherical data (random points on a unit sphere) are a recent development. An overview of existing graphical methods for the display of directional data is given. Cross-over occurs when periodic data are measured on a scale for the measurement of linear variables. For example, if angle is represented by a linear color gradient changing uniformly from dark blue at -180 degrees to bright red at +180 degrees, the color image will be discontinuous at +180 degrees and -180 degrees, which are the same location. The resultant color would depend on the direction of approach to the cross-over point. A new graphical method for imaging directional data is described, which affords high resolution without color discontinuity from "cross-over". It is called the circular data image. The circular data image uses a circular color scale in which colors repeat periodically. Some examples of the circular data image include direction of earth winds on a global scale, rocket motor internal flow, earth global magnetic field direction, and rocket motor nozzle vector direction vs. time.

Morpet, William J.↗

Rapid magnetic reconnection caused by finite amplitude fluctuations

The nonlinear dynamics of the magnetohydrodynamic sheet pinch have been investigated as an unforced initial value problem for large scale Reynolds numbers up to 1000. Reconnection is triggered by adding to the sheet pinch a small but finite level of broadband random perturbations. Effects of turbulence in the solutions include the production of reconnected magnetic islands at rates that are insensitive to resistivity at early times. This is explained by noting that electric field fluctuations near the X point produce irregularities in the vector potential, sometimes taking the form of 'magnetic bubbles', which allow rapid change of field topology.

Matthaeus, W. H.↗

The Kelvin-Helmholtz instability at the magnetopause and inner boundary layer surface

Observations by the vector electron spectrometer on the ISEE 1 spacecraft are used to directly check the incompressible hydromagnetic stability condition given by Hasegawa (1975), which indicates how stability is influenced by the velocity shear, density ratio, magnetic field, and the direction of the wave vector of the unstable wave mode. The magnetopause is generally found to be stable, by a large margin. In contrast, many cases of marginal stability or instability are found across density transitions in, and at the inner edge of, the boundary layer for wave vectors in plausible directions. It thus appears that the Kelvin-Helmholtz instability is of importance at the inner edge of the magnetospheric boundary layer, as predicted by MHP theory.

Ogilvie, Keith W.↗

Studies of the marine crustal magnetization at intermediate wavelengths

The data can be filtered at intermediate wavelengths to provde a data set which complements the satellite fields of MAGSAT, TSS and GRM. The filtered marine data set provides a high resolution data set which is closer to the source bodies than satellite survey data. However, the GRM and TSS could provide the necessary resolution to match the filtered sea surface field. The added resolution determines the nature of crustal magnetizations which give rise to the intermediate wavelength field. It is found that remanent magnetization is an important component over the oceans. Crustal deformation and plate motions result in magnetization vectors which differ significantly from the present day field directions. Induced magnetization or GRM are important components over the oceanic plateaus and spreading centers.

Labrecque, J. L.↗

Conversion of magnetic field energy into kinetic energy in the solar wind

The outflow of the solar magnetic field energy (the radial component of the Poynting vector) per steradian is inversely proportional to the solar wind velocity. It is a decreasing function of the heliocentric distance. When the magnetic field effect is included in the one-fluid model of the solar wind, the transformation of magnetic field energy into kinetic energy during the expansion process increases the solar wind velocity at 1 AU by 17 percent.

Whang, Y. C.↗