Multispectral Emission of the Sun during the First Whole Sun Month: Magnetohydrodynamic Simulations
NASA Technical Reports Server (NTRS)
Lionello, Roberto; Linker, Jon A.; Mikic, Zoran
2008-01-01
We demonstrate that a three-dimensional magnetohydrodynamic (MHD) simulation of the corona can model its global plasma density and temperature structure with sufficient accuracy to reproduce many of the multispectral properties of the corona observed in extreme ultraviolet (EW) and X-ray emission. The key ingredient to this new type of global MHD model is the inclusion of energy transport processes (coronal heating, anisotropic thermal conduction, and radiative losses) in the energy equation. The calculation of these processes has previously been confined to one-dimensional loop models, idealized two-dimensional computations, and three-dimensional active region models. We refer to this as the thermodynamic MHD model, and we apply it to the time period of Carrington rotation 1913 (1996 August 22 to September 18). The form of the coronal heating term strongly affects the plasma density and temperature of the solutions. We perform our calculation for three different empirical heating models: (1) a heating function exponentially decreasing in radius; (2) the model of Schrijver et al.; and (3) a model reproducing the heating properties of the quiet Sun and active regions. We produce synthetic emission images from the density and temperature calculated with these three heating functions and quantitatively compare them with observations from E W Imaging Telescope on the Solar and Heliospheric Observatory and the soft X-ray telescope on Yohkoh. Although none of the heating models provide a perfect match, heating models 2 and 3 provide a reasonable match to the observations.
This multi-wavelength movie of the Sun covers seven months of activity (April 25 - Nov. 30, 2011), the majority of the SDO mission to date. The frames combine images taken at the same time in three...
Magnetohydrodynamic Modelling of Interplanetary Disturbances between the Sun and Earth.
1982-12-21
34, of W¢:dia l Solor Wind Vrloc ity, i)hnsitx, "]’rTpOT- Iir~u, :InVl I)l;I1 I.MI’ "\\h~ritudr. at 0.3 Al’. (n) - (d) (’Il ol’ flUSO-g(fl(nAVt,’T :h k...no.n - -,0,0 do If-ncon.ry *d ideIly by’ block -el,) 1111) modelling lar wind norplanetnrY disturbhance 20 ABSTRACT (CroIffI, 1n -esrO side It ~cls...magnetosphere. The "canonical" or anzatz series of 3hock wA ves include initial velocities near the sun over the range 500 to 3000 (m sec . The ambient solar wind
Savcheva, A.; Van Ballegooijen, A.; DeLuca, E.; Pariat, E.; Aulanier, G.
2012-05-01
In this paper we show that when accurate nonlinear force-free field (NLFFF) models are analyzed together with high-resolution magnetohydrodynamic (MHD) simulations, we can determine the physical causes for the coronal mass ejection (CME) eruption on 2007 February 12. We compare the geometrical and topological properties of the three-dimensional magnetic fields given by both methods in their pre-eruptive phases. We arrive at a consistent picture for the evolution and eruption of the sigmoid. Both the MHD simulation and the observed magnetic field evolution show that flux cancellation plays an important role in building the flux rope. We compute the squashing factor, Q, in different horizontal maps in the domains. The main shape of the quasi-separatrix layers (QSLs) is very similar between the NLFFF and MHD models. The main QSLs lie on the edge of the flux rope. While the QSLs in the NLFFF model are more complex due to the intrinsic large complexity in the field, the QSLs in the MHD model are smooth and possess lower maximum value of Q. In addition, we demonstrate the existence of hyperbolic flux tubes (HFTs) in both models in vertical cross sections of Q. The main HFT, located under the twisted flux rope in both models, is identified as the most probable site for reconnection. We also show that there are electric current concentrations coinciding with the main QSLs. Finally, we perform torus instability analysis and show that a combination between reconnection at the HFT and the resulting expansion of the flux rope into the torus instability domain is the cause of the CME in both models.
Spectroscopic observations of the extended corona during the SOHO whole sun month
NASA Technical Reports Server (NTRS)
Strachan, L.; Raymond, J. C.; Panasyuk, A. V.; Fineschi, S.; Gardner, L. D.; Antonucci, E.; Giordano, S.; Romoli, M.; Noci, G.; Kohl, J. L.
1997-01-01
The spatial distribution of plasma parameters in the extended corona, derived from the ultraviolet coronagraph spectrometer (UVCS) onboard the Solar and Heliospheric Observatory (SOHO), was investigated. The observations were carried out during the SOHO whole month campaign. Daily coronal scans in the H I Lyman alpha and O VI lambda-lambda 1032 A and 1037 A were used. Maps of outflow velocities of O(5+), based on Doppler dimming of the O VI lines, are discussed. The velocity distribution widths of O(5+) are shown to be a clear signature of coronal holes while the velocity distributions for H(0) show a much smaller effect. The possible physical explanations for some of the observed features are discussed.
NASA Astrophysics Data System (ADS)
Murdin, P.
2000-11-01
A unit of time based on the motion of the Moon around the Earth. The synodic (or lunar) month is the mean time interval between two successive new moons (i.e. the time taken for the Moon to pass through its cycle of phases) and is equal to 29.53059 mean solar days. Because the synodic month (the basis of the lunar calendar) is not equal to a whole number of days, the calendar month is rounded to ...
Haas, Fernando; Pascoal, Kellen Alves; Mendonça, José Tito
2016-01-15
A new neutrino magnetohydrodynamics (NMHD) model is formulated, where the effects of the charged weak current on the electron-ion magnetohydrodynamic fluid are taken into account. The model incorporates in a systematic way the role of the Fermi neutrino weak force in magnetized plasmas. A fast neutrino-driven short wavelengths instability associated with the magnetosonic wave is derived. Such an instability should play a central role in strongly magnetized plasma as occurs in supernovae, where dense neutrino beams also exist. In addition, in the case of nonlinear or high frequency waves, the neutrino coupling is shown to be responsible for breaking the frozen-in magnetic field lines condition even in infinite conductivity plasmas. Simplified and ideal NMHD assumptions were adopted and analyzed in detail.
Boquist, Carl W.; Marchant, David D.
1978-01-01
A ceramic-metal composite suitable for use in a high-temperature environment consists of a refractory ceramic matrix containing 10 to 50 volume percent of a continuous high-temperature metal reinforcement. In a specific application of the composite, as an electrode in a magnetohydrodynamic generator, the one surface of the electrode which contacts the MHD fluid may have a layer of varying thickness of nonreinforced refractory ceramic for electrode temperature control. The side walls of the electrode may be coated with a refractory ceramic insulator. Also described is an electrode-insulator system for a MHD channel.
Magnetohydrodynamic instability
NASA Technical Reports Server (NTRS)
Priest, E. R.; Cargill, P.; Forbes, T. G.; Hood, A. W.; Steinolfson, R. S.
1986-01-01
There have been major advances in the theory of magnetic reconnection and of magnetic instability, with important implications for the observations, as follows: (1) Fast and slow magnetic shock waves are produced by the magnetohydrodynamics of reconnection and are potential particle accelerators. (2) The impulsive bursty regime of reconnection gives a rapid release of magnetic energy in a series of bursts. (3) The radiative tearing mode creates cool filamentary structures in the reconnection process. (4) The stability analyses imply that an arcade can become unstable when either its height or twist of plasma pressure become too great.
Marchant, David D.; Killpatrick, Don H.
1978-01-01
An electrode capable of withstanding high temperatures and suitable for use as a current collector in the channel of a magnetohydrodynamic (MHD) generator consists of a sintered powdered metal base portion, the upper surface of the base being coated with a first layer of nickel aluminide, an intermediate layer of a mixture of nickel aluminide - refractory ceramic on the first layer and a third or outer layer of a refractory ceramic material on the intermediate layer. The sintered powdered metal base resists spalling by the ceramic coatings and permits greater electrode compliance to thermal shock. The density of the powdered metal base can be varied to allow optimization of the thermal conductivity of the electrode and prevent excess heat loss from the channel.
Magnetohydrodynamic Turbulence
NASA Astrophysics Data System (ADS)
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Solar Flares: Magnetohydrodynamic Processes
NASA Astrophysics Data System (ADS)
Shibata, Kazunari; Magara, Tetsuya
2011-12-01
This paper outlines the current understanding of solar flares, mainly focused on magnetohydrodynamic (MHD) processes responsible for producing a flare. Observations show that flares are one of the most explosive phenomena in the atmosphere of the Sun, releasing a huge amount of energy up to about 1032 erg on the timescale of hours. Flares involve the heating of plasma, mass ejection, and particle acceleration that generates high-energy particles. The key physical processes for producing a flare are: the emergence of magnetic field from the solar interior to the solar atmosphere (flux emergence), local enhancement of electric current in the corona (formation of a current sheet), and rapid dissipation of electric current (magnetic reconnection) that causes shock heating, mass ejection, and particle acceleration. The evolution toward the onset of a flare is rather quasi-static when free energy is accumulated in the form of coronal electric current (field-aligned current, more precisely), while the dissipation of coronal current proceeds rapidly, producing various dynamic events that affect lower atmospheres such as the chromosphere and photosphere. Flares manifest such rapid dissipation of coronal current, and their theoretical modeling has been developed in accordance with observations, in which numerical simulations proved to be a strong tool reproducing the time-dependent, nonlinear evolution of a flare. We review the models proposed to explain the physical mechanism of flares, giving an comprehensive explanation of the key processes mentioned above. We start with basic properties of flares, then go into the details of energy build-up, release and transport in flares where magnetic reconnection works as the central engine to produce a flare.
Magnetohydrodynamic Turbulence and the Geodynamo
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2014-01-01
The ARES Directorate at JSC has researched the physical processes that create planetary magnetic fields through dynamo action since 2007. The "dynamo problem" has existed since 1600, when William Gilbert, physician to Queen Elizabeth I, recognized that the Earth was a giant magnet. In 1919, Joseph Larmor proposed that solar (and by implication, planetary) magnetism was due to magnetohydrodynamics (MHD), but full acceptance did not occur until Glatzmaier and Roberts solved the MHD equations numerically and simulated a geomagnetic reversal in 1995. JSC research produced a unique theoretical model in 2012 that provided a novel explanation of these physical observations and computational results as an essential manifestation of broken ergodicity in MHD turbulence. Research is ongoing, and future work is aimed at understanding quantitative details of magnetic dipole alignment in the Earth as well as in Mercury, Jupiter and its moon Ganymede, Saturn, Uranus, Neptune, and the Sun and other stars.
Experiments in Magnetohydrodynamics
ERIC Educational Resources Information Center
Rayner, J. P.
1970-01-01
Describes three student experiments in magnetohydrodynamics (MHD). In these experiments, it was found that the electrical conductivity of the local water supply was sufficient to demonstrate effectively some of the features of MHD flowmeters, generators, and pumps. (LC)
Magnetohydrodynamic cellular automata
NASA Technical Reports Server (NTRS)
Montgomery, David; Doolen, Gary D.
1987-01-01
A generalization of the hexagonal lattice gas model of Frisch, Hasslacher and Pomeau is shown to lead to two-dimensional magnetohydrodynamics. The method relies on the ideal point-wise conservation law for vector potential.
Magnetohydrodynamic power generation
NASA Technical Reports Server (NTRS)
Smith, J. L.
1984-01-01
Magnetohydrodynamic (MHD) Power Generation is a concise summary of MHD theory, history, and future trends. Results of the major international MHD research projects are discussed. Data from MHD research is included. Economics of initial and operating costs are considered.
Gyroscopic analog for magnetohydrodynamics
Holm, D.D.
1981-01-01
The gross features of plasma equilibrium and dynamics in the ideal magnetohydrodynamics (MHD) model can be understood in terms of a dynamical system which closely resembles the equations for a deformable gyroscope.
NASA Technical Reports Server (NTRS)
Whang, Y. C.
1982-01-01
It is inferred from this study that magnetohydrodynamic slow shocks can exist in the vicinity of the sun. The study uses a two-hole corona model, the sub-Alfvenic streams originating from the edge of the polar open-field regions are forced to turn towards equator in coronal space following the curved boundary of the closed field region. When the streamlines from the opposite poles merge at a neutral point, their directions become parallel to the neutral sheet. An oblique slow shock can develop near or at the neutral point, the shock extends polewards to form a surface of discontinuity around the sun.
Magnetohydrodynamic fluidic system
Lee, Abraham P.; Bachman, Mark G.
2004-08-24
A magnetohydrodynamic fluidic system includes a reagent source containing a reagent fluid and a sample source containing a sample fluid that includes a constituent. A reactor is operatively connected to the supply reagent source and the sample source. MHD pumps utilize a magnetohydrodynamic drive to move the reagent fluid and the sample fluid in a flow such that the reagent fluid and the sample fluid form an interface causing the constituent to be separated from the sample fluid.
Introduction to Modern Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Galtier, Sébastien
2016-10-01
Preface; Table of physical quantities; Part I. Foundations: 1. Introduction; 2. Magnetohydrodynamics; 3. Conservation laws; Part II. Fundamental Processes: 4. Magnetohydrodynamic waves; 5. Dynamo; 6. Discontinuities and shocks; 7. Magnetic reconnection; Part III. Instabilities and Magnetic Confinement: 8. Static equilibrium; 9. Linear perturbation theory; 10. Study of MHD instabilities; Part IV. Turbulence: 11. Hydrodynamic turbulence; 12. MHD turbulence; 13. Advanced MHD turbulence; Appendix 1. Solutions to the exercises; Appendix 2. Formulary; References; Index.
Nonlinear magnetohydrodynamic stability
NASA Technical Reports Server (NTRS)
Bauer, F.; Betancourt, O.; Garabedian, P.
1981-01-01
The computer code developed by Bauer et al. (1978) for the study of the magnetohydrodynamic equilibrium and stability of a plasma in toroidal geometry is extended so that the growth rates of instabilities may be estimated more accurately. The original code, which is based on the variational principle of ideal magnetohydrodynamics, is upgraded by the introduction of a nonlinear formula for the growth rate of an unstable mode which acts as a quantitative measure of instability that is important in estimating numerical errors. The revised code has been applied to the determination of the nonlinear saturation, ballooning modes and beta limits for tokamaks, stellarators and torsatrons.
ERIC Educational Resources Information Center
Petersen, Hugh
2010-01-01
The Aztec Sun Stone is a revered Mexican artifact. It is said to be perhaps the most famous symbol of Mexico, besides its flag. It primarily depicts the four great disasters that led to the migration of the Mexica people to modern-day Mexico City. The Aztec Sun Stone also contains pictographs depicting the way the Mexica measured time, and was…
Thermoacoustic magnetohydrodynamic electrical generator
Wheatley, John C.; Swift, Gregory W.; Migliori, Albert
1986-01-01
A thermoacoustic magnetohydrodynamic electrical generator includes an intrinsically irreversible thermoacoustic heat engine coupled to a magnetohydrodynamic electrical generator. The heat engine includes an electrically conductive liquid metal as the working fluid and includes two heat exchange and thermoacoustic structure assemblies which drive the liquid in a push-pull arrangement to cause the liquid metal to oscillate at a resonant acoustic frequency on the order of 1,000 Hz. The engine is positioned in the field of a magnet and is oriented such that the liquid metal oscillates in a direction orthogonal to the field of the magnet, whereby an alternating electrical potential is generated in the liquid metal. Low-loss, low-inductance electrical conductors electrically connected to opposite sides of the liquid metal conduct an output signal to a transformer adapted to convert the low-voltage, high-current output signal to a more usable higher voltage, lower current signal.
Thermoacoustic magnetohydrodynamic electrical generator
Wheatley, J.C.; Swift, G.W.; Migliori, A.
1984-11-16
A thermoacoustic magnetohydrodynamic electrical generator includes an intrinsically irreversible thermoacoustic heat engine coupled to a magnetohydrodynamic electrical generator. The heat engine includes an electrically conductive liquid metal as the working fluid and includes two heat exchange and thermoacoustic structure assemblies which drive the liquid in a push-pull arrangement to cause the liquid metal to oscillate at a resonant acoustic frequency on the order of 1000 Hz. The engine is positioned in the field of a magnet and is oriented such that the liquid metal oscillates in a direction orthogonal to the field of the magnet, whereby an alternating electrical potential is generated in the liquid metal. Low-loss, low-inductance electrical conductors electrically connected to opposite sides of the liquid metal conduct an output signal to a transformer adapted to convert the low-voltage, high-current output signal to a more usable higher voltage, lower current signal.
AC magnetohydrodynamic microfluidic switch
Lemoff, A V; Lee, A P
2000-03-02
A microfluidic switch has been demonstrated using an AC Magnetohydrodynamic (MHD) pumping mechanism in which the Lorentz force is used to pump an electrolytic solution. By integrating two AC MHD pumps into different arms of a Y-shaped fluidic circuit, flow can be switched between the two arms. This type of switch can be used to produce complex fluidic routing, which may have multiple applications in {micro}TAS.
Interactions between magnetohydrodynamical discontinuities
Dai, W.; Woodward, P.R. )
1994-11-01
Interactions between magnetohydrodynamical (MHD) discontinuities are studied through numerical simulations for the set of one-dimensional MHD equations. The interactions include the impact of a shock on a contact discontinuity, the collision of two shocks, and the catchup of a shock over another shock. The shocks involved in the interactions may be very strong. Each shock in an interaction may be either a fast or a slow shock.
Future of Magnetohydrodynamic Ship Propulsion,
1983-08-16
83 FOREIGN TECHNOLOGY DIVISION FUTURE OF MAGNETOHYDRODYNAMIC SHIP PROPULSION by A.P. Baranov DTIQ ~E tJ Approved for public release; 0.. distribution...MAGNETOHYDRODYNAMIC SHIP PROPULSION By: A.P. Baranov -,English pages: 10 Source: Sudostroyeniye, Nr. 12, December 1966, pp. 3-6 . Country of origin: USSR X...equations, etc. merged into this translation were extracted from the best quality copy available. FUTURE OF MAGNETOHYDRODYNAMIC SHIP PROPULSION A. P
NASA Technical Reports Server (NTRS)
Guhathakurta, M.; Fludra, A.; Gibson, S. E.; Biesecker, D.; Fisher, R.
2004-01-01
Until recently, inference of electron density distribution in the solar corona was limited by the field of view of white-light coronagraphs (typically out to 6 Rs). Now, for the first time we have a series of white- light coronagraphs (SOHO/LASCO) whose combined field of view extends from 1.1 - 30 Rs. Quantitative information on electron density distribution of coronal hole and coronal plumes/rays are estimated by using white-light, polarized brightness (pB) observations from the SOHO/LASCO/C2 and C3 and HAO/Mauna Loa Mark III coronagraphs from 1.15 to 8.0 Rs. Morphological information on the boundary of the polar coronal hole and streamer interface is determined from the white-light observations in a manner similar to the Skylab polar coronal hole boundary estimate. The average coronal hole electron density in the region 1 - 1.15 Rs is estimated from the density-sensitive EUV line ratios of Si IX 3501342 A observed by the SOHO/coronal diagnostic spectrometer (CDS). We combine these numbers with the estimate from white-light (WL) observations to obtain a density profile from 1 to 8 Rs for the plumes and the polar coronal hole. We find that white light and spectral analysis produce consistent density information. Extrapolated densities inferred from SOHO observations are compared to Ulysses in situ observations of density. Like the density inferred from the Spartan 201-03 coronagraph, the current SOHO density profiles suggest that the acceleration of the fast solar wind takes place very close to the Sun, within 10-15 Rs. The density information is used to put constraints on solar wind flow velocities and effective temperatures. Finally, these results are compared to the recent analysis of the Spartan 201-03 white-light observations.
... occurs on skin that has been exposed to sunlight. The most common form of sun allergy is ... have unusual, bothersome skin reactions after exposure to sunlight. For severe or persistent symptoms, you may need ...
Younskevicius, Robert E.
1978-01-01
A simple, inexpensive device for measuring the radiation energy of the sun impinging on the device. The measurement of the energy over an extended period of time is accomplished without moving parts or tracking mechanisms.
... Links Buttons and Badges Stay Informed Cancer Home Sun Safety Language: English Español (Spanish) Recommend on Facebook Tweet Share Compartir The sun’s ultraviolet (UV) rays can damage your skin in ...
... pass through your skin and damage your skin cells. Sunburns are a sign of skin damage. Suntans ... after the sun's rays have already killed some cells and damaged others. UV rays can cause skin ...
Magnetohydrodynamics of fractal media
Tarasov, Vasily E.
2006-05-15
The fractal distribution of charged particles is considered. An example of this distribution is the charged particles that are distributed over the fractal. The fractional integrals are used to describe fractal distribution. These integrals are considered as approximations of integrals on fractals. Typical turbulent media could be of a fractal structure and the corresponding equations should be changed to include the fractal features of the media. The magnetohydrodynamics equations for fractal media are derived from the fractional generalization of integral Maxwell equations and integral hydrodynamics (balance) equations. Possible equilibrium states for these equations are considered.
MAGNETOHYDRODYNAMICS OF THE WEAKLY IONIZED SOLAR PHOTOSPHERE
Cheung, Mark C. M.; Cameron, Robert H.
2012-05-01
We investigate the importance of ambipolar diffusion and Hall currents for high-resolution comprehensive ({sup r}ealistic{sup )} photospheric simulations. To do so, we extended the radiative magnetohydrodynamics code MURaM to use the generalized Ohm's law under the assumption of local thermodynamic equilibrium. We present test cases comparing analytical solutions with numerical simulations for validation of the code. Furthermore, we carried out a number of numerical experiments to investigate the impact of these neutral-ion effects in the photosphere. We find that, at the spatial resolutions currently used (5-20 km per grid point), the Hall currents and ambipolar diffusion begin to become significant-with flows of 100 m s{sup -1} in sunspot light bridges, and changes of a few percent in the thermodynamic structure of quiet-Sun magnetic features. The magnitude of the effects is expected to increase rapidly as smaller-scale variations are resolved by the simulations.
NASA Technical Reports Server (NTRS)
Habbal, S. R.; Leer, E.
1982-01-01
It is shown that fast mode magnetohydrodynamic waves, propagating outwards from the sun in coronal hole regions, will dissipate primarily through collisionless interaction with electrons rather than with protons. This dissipation can lead to higher electron than proton temperatures in the accelerating region of the solar wind, provided the waves carry a sufficiently large energy flux.
Conservation of circulation in magnetohydrodynamics
Bekenstein; Oron
2000-10-01
We demonstrate at both the Newtonian and (general) relativistic levels the existence of a generalization of Kelvin's circulation theorem (for pure fluids) that is applicable to perfect magnetohydrodynamics. The argument is based on the least action principle for magnetohydrodynamic flow. Examples of the new conservation law are furnished. The new theorem should be helpful in identifying new kinds of vortex phenomena distinct from magnetic ropes or fluid vortices.
Magnetohydrodynamic Augmented Propulsion Experiment
NASA Technical Reports Server (NTRS)
Litchford, Ron J.; Cole, John; Lineberry, John; Chapman, Jim; Schmidt, Harold; Cook, Stephen (Technical Monitor)
2002-01-01
A fundamental obstacle to routine space access is the specific energy limitations associated with chemical fuels. In the case of vertical take-off, the high thrust needed for vertical liftoff and acceleration to orbit translates into power levels in the 10 GW range. Furthermore, useful payload mass fractions are possible only if the exhaust particle energy (i.e., exhaust velocity) is much greater than that available with traditional chemical propulsion. The electronic binding energy released by the best chemical reactions (e.g., LOX/LH2 for example, is less than 2 eV per product molecule (approx. 1.8 eV per H2O molecule), which translates into particle velocities less than 5 km/s. Useful payload fractions, however, will require exhaust velocities exceeding 15 km/s (i.e., particle energies greater than 20 eV). As an added challenge, the envisioned hypothetical RLV (reusable launch vehicle) should accomplish these amazing performance feats while providing relatively low acceleration levels to orbit (2-3g maximum). From such fundamental considerations, it is painfully obvious that planned and current RLV solutions based on chemical fuels alone represent only a temporary solution and can only result in minor gains, at best. What is truly needed is a revolutionary approach that will dramatically reduce the amount of fuel and size of the launch vehicle. This implies the need for new compact high-power energy sources as well as advanced accelerator technologies for increasing engine exhaust velocity. Electromagnetic acceleration techniques are of immense interest since they can be used to circumvent the thermal limits associated with conventional propulsion systems. This paper describes the Magnetohydrodynamic Augmented Propulsion Experiment (MAPX) being undertaken at NASA Marshall Space Flight Center (MSFC). In this experiment, a 1-MW arc heater is being used as a feeder for a 1-MW magnetohydrodynamic (MHD) accelerator. The purpose of the experiment is to demonstrate
Multi-symplectic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Webb, G. M.; McKenzie, J. F.; Zank, G. P.; Zank
2014-10-01
A multi-symplectic formulation of ideal magnetohydrodynamics (MHD) is developed based on the Clebsch variable variational principle in which the Lagrangian consists of the kinetic minus the potential energy of the MHD fluid modified by constraints using Lagrange multipliers that ensure mass conservation, entropy advection with the flow, the Lin constraint, and Faraday's equation (i.e. the magnetic flux is Lie dragged with the flow). The analysis is also carried out using the magnetic vector potential Ã where α=Ã. d x is Lie dragged with the flow, and B=∇×Ã. The multi-symplectic conservation laws give rise to the Eulerian momentum and energy conservation laws. The symplecticity or structural conservation laws for the multi-symplectic system corresponds to the conservation of phase space. It corresponds to taking derivatives of the momentum and energy conservation laws and combining them to produce n(n-1)/2 extra conservation laws, where n is the number of independent variables. Noether's theorem for the multi-symplectic MHD system is derived, including the case of non-Cartesian space coordinates, where the metric plays a role in the equations.
Filamentary magnetohydrodynamic plasmas
Kinney, R.; Tajima, T.; Petviashvili, N.; McWilliams, J.C.
1993-05-01
A filamentary construct of magnetohydrodynamical plasma dynamics, based on the Elsasser variables was developed. This approach is modeled after discrete vortex models of hydrodynamical turbulence, which cannot be expected in general to produce results identical to ones based on a Fourier decomposition of the fields. In a highly intermittent plasma, the induction force is small compared to the convective motion, and when this force is neglected. the plasma vortex system is described by a Hamiltonian. For a system with many such vortices we present a statistical treatment of a collection of discrete current-vorticity concentrations. Canonical and microcanonical statistical calculations show that both the vorticity and the current spectra are peaked at long wavelengths, and the expected states revert to known hydrodynamical states as the magnetic field vanishes. These results differ from previous Fourier-based statistical theories. but it is found that when the filament calculation is expanded to include the inductive force, the results approach the Fourier equilibria in the low-temperature limit, and the previous Hamiltonian plasma vortex results in the high-temperature limit. Numerical simulations of a large number of filaments are carried out and support the theory. A three-dimensional vortex model is outlined as well, which is also Hamiltonian when the inductive force is neglected.
Magnetohydrodynamics in Materials Processing
NASA Astrophysics Data System (ADS)
Davidson, P. A.
1999-01-01
Magnetic fields can be used to melt, pump, stir, and stabilize liquid metals. This provides a nonintrusive means of controlling the flow of metal in commercial casting and refining operations. The quest for greater efficiency and more control in the production of steel, aluminum, and high-performance superalloys has led to a revolution in the application of magnetohydrodynamics (MHD) to process metallurgy. Three typical applications are described here, chosen partially on the basis of their general interest to fluid dynamicists, and partially because of their considerable industrial importance. We look first at magnetic stirring, where a rotating magnetic field is used to agitate and homogenize the liquid zone of a partially-solidified ingot. This is a study in Ekman pumping. Next, we consider magnetic damping, where an intense, static magnetic field is used to suppress fluid motion. In particular, we look at the damping of jets, vortices, and turbulence. We conclude with a discussion of the magnetic destabilization of liquid-liquid interfaces. This is of particular importance in aluminum production.
NASA Technical Reports Server (NTRS)
Adams, Mitzi L.; Mortfield, P.; Hathaway, D. H.; Whitaker, Ann F. (Technical Monitor)
2001-01-01
To promote awareness of the Sun-Earth connection, NASA's Marshall Space Flight Center, in collaboration with the Stanford SOLAR Center, sponsored a one-day Sun-Earth Day event on April 27, 2001. Although "celebrated" on only one day, teachers and students from across the nation, prepared for over a month in advance. Workshops were held in March to train teachers. Students performed experiments, results of which were shared through video clips and an internet web cast. Our poster includes highlights from student experiments (grades 2 - 12), lessons learned from the teacher workshops and the event itself, and plans for Sun-Earth Day 2002.
Time-dependent magnetohydrodynamic simulations of the inner heliosphere
NASA Astrophysics Data System (ADS)
Merkin, V. G.; Lyon, J. G.; Lario, D.; Arge, C. N.; Henney, C. J.
2016-04-01
This paper presents results from a simulation study exploring heliospheric consequences of time-dependent changes at the Sun. We selected a 2 month period in the beginning of year 2008 that was characterized by very low solar activity. The heliosphere in the equatorial region was dominated by two coronal holes whose changing structure created temporal variations distorting the classical steady state picture of the heliosphere. We used the Air Force Data Assimilate Photospheric Flux Transport (ADAPT) model to obtain daily updated photospheric magnetograms and drive the Wang-Sheeley-Arge (WSA) model of the corona. This leads to a formulation of a time-dependent boundary condition for our three-dimensional (3-D) magnetohydrodynamic (MHD) model, LFM-helio, which is the heliospheric adaptation of the Lyon-Fedder-Mobarry MHD simulation code. The time-dependent coronal conditions were propagated throughout the inner heliosphere, and the simulation results were compared with the spacecraft located near 1 astronomical unit (AU) heliocentric distance: Advanced Composition Explorer (ACE), Solar Terrestrial Relations Observatory (STEREO-A and STEREO-B), and the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft that was in cruise phase measuring the heliospheric magnetic field between 0.35 and 0.6 AU. In addition, during the selected interval MESSENGER and ACE aligned radially allowing minimization of the effects of temporal variation at the Sun versus radial evolution of structures. Our simulations show that time-dependent simulationsreproduce the gross-scale structure of the heliosphere with higher fidelity, while on smaller spatial and faster time scales (e.g., 1 day) they provide important insights for interpretation of the data. The simulations suggest that moving boundaries of slow-fast wind transitions at 0.1 AU may result in the formation of inverted magnetic fields near pseudostreamers which is an intrinsically time-dependent process
Compressible magnetohydrodynamic sawtooth crash
NASA Astrophysics Data System (ADS)
Sugiyama, Linda E.
2014-02-01
In a toroidal magnetically confined plasma at low resistivity, compressible magnetohydrodynamic (MHD) predicts that an m = 1/n = 1 sawtooth has a fast, explosive crash phase with abrupt onset, rate nearly independent of resistivity, and localized temperature redistribution similar to experimental observations. Large scale numerical simulations show that the 1/1 MHD internal kink grows exponentially at a resistive rate until a critical amplitude, when the plasma motion accelerates rapidly, culminating in fast loss of the temperature and magnetic structure inside q < 1, with somewhat slower density redistribution. Nonlinearly, for small effective growth rate the perpendicular momentum rate of change remains small compared to its individual terms ∇p and J × B until the fast crash, so that the compressible growth rate is determined by higher order terms in a large aspect ratio expansion, as in the linear eigenmode. Reduced MHD fails completely to describe the toroidal mode; no Sweet-Parker-like reconnection layer develops. Important differences result from toroidal mode coupling effects. A set of large aspect ratio compressible MHD equations shows that the large aspect ratio expansion also breaks down in typical tokamaks with rq =1/Ro≃1/10 and a /Ro≃1/3. In the large aspect ratio limit, failure extends down to much smaller inverse aspect ratio, at growth rate scalings γ =O(ɛ2). Higher order aspect ratio terms, including B˜ϕ, become important. Nonlinearly, higher toroidal harmonics develop faster and to a greater degree than for large aspect ratio and help to accelerate the fast crash. The perpendicular momentum property applies to other transverse MHD instabilities, including m ≥ 2 magnetic islands and the plasma edge.
GRIM: General Relativistic Implicit Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Chandra, Mani; Foucart, Francois; Gammie, Charles F.
2017-02-01
GRIM (General Relativistic Implicit Magnetohydrodynamics) evolves a covariant extended magnetohydrodynamics model derived by treating non-ideal effects as a perturbation of ideal magnetohydrodynamics. Non-ideal effects are modeled through heat conduction along magnetic field lines and a difference between the pressure parallel and perpendicular to the field lines. The model relies on an effective collisionality in the disc from wave-particle scattering and velocity-space (mirror and firehose) instabilities. GRIM, which runs on CPUs as well as on GPUs, combines time evolution and primitive variable inversion needed for conservative schemes into a single step using only the residuals of the governing equations as inputs. This enables the code to be physics agnostic as well as flexible regarding time-stepping schemes.
[Nonlinear magnetohydrodynamics]. Final report
Montgomery, D.C.
1998-11-01
This is a final report on the research activities carried out under the above grant at Dartmouth. During the period considered, the grant was identified as being for nonlinear magnetohydrodynamics, considered as the most tractable theoretical framework in which the plasma problems associated with magnetic confinement of fusion plasmas could be studied. During the first part of the grant`s lifetime, the author was associated with Los Alamos National Laboratory as a consultant and the work was motivated by the reversed-field pinch. Later, when that program was killed at Los Alamos, the problems became ones that could be motivated by their relation to tokamaks. Throughout the work, the interest was always on questions that were as fundamental as possible, compatible with those motivations. The intent was always to contribute to plasma physics as a science, as well as to the understanding of mission-oriented confined fusion plasmas. Twelve Ph.D. theses were supervised during this period and a comparable number of postdoctoral research associates were temporarily supported. Many of these have gone on to distinguished careers, though few have done so in the context of the controlled fusion program. Their work was a combination of theory and numerical computation, in gradually less and less idealized settings, moving from rectangular periodic boundary conditions in two dimensions, through periodic straight cylinders and eventually, before the grant was withdrawn, to toroids, with a gradually more prominent role for electrical and mechanical boundary conditions. The author never had access to a situation where he could initiate experiments and relate directly to the laboratory data he wanted. Computers were the laboratory. Most of the work was reported in referred publications in the open literature, copies of which were transmitted one by one to DOE at the time they appeared. The Appendix to this report is a bibliography of published work which was carried out under the
ERIC Educational Resources Information Center
Hagen, Patricia; Ingram, Dabney
2004-01-01
Providing sun-safe environments, schedules, and activities; teaching and modeling sun-safe behaviors; and implementing a sun-safe school policy are ways that schools can help protect children from sun overexposure and lay the foundation for a healthy lifestyle at an early age. This article presents the SunWise program and examples of classroom…
NASA Technical Reports Server (NTRS)
Liebe, C. C.; Mobasser, S.; Wrigley, C. J.; Bae, Y.; Howard, A.; Schroeder, J.
2002-01-01
A new generation of sun sensors is emerging. These sun sensors utilize an imaging detector and the sun sensor determines the sun angles based on an image of fringes or centroids on the detector plane. Typically determines the sun angle in two axes.
Action Principle for Relativistic Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
D'Avignon, Eric; Morrison, Philip; Pegoraro, Francesco
2015-11-01
A covariant action principle for ideal relativistic magnetohydrodynamics in terms of natural Eulerian field variables is given. This is done by generalizing the covariant Poisson bracket theory of Marsden et al., which uses a noncanonical bracket to implement constrained variations of an action functional. Various implications and extensions of this action principle are also discussed.
ERIC Educational Resources Information Center
Hemenway, Mary Kay
2000-01-01
Presents activities for elementary and middle school students on the sun and the Earth-sun relationship. Studies the structure of the sun with activities that include Shadow Play, Reflective Solar Cooker, Equatorial Sundial, and Tracing Images. (YDS)
Global magnetohydrodynamic simulations of the magnetosphere
Walker, R.J.; Ogino, T.
1989-04-01
Global magnetohydrodynamic (MHD) simulations of the interaction between the solar wind and a planetary magnetosphere enable us to calculate self-consistently the time-dependent three-dimensional configuration of the magnetosphere. To demonstrate the application of a global MHD model to the magnetosphere, the authors have calculated the dependence of the magnetospheric configuration and polar-cap structure on the north-south component of the interplanetary magnetic field (IMF). First, they modeled the magnetosphere in the absence of an IMF and found a slowly evolving system in which steady convection leads to slow reconnection in the plasma sheet. When a uniform northward IMF was initially imposed throughout the system the plasma sheet thickened in a small region near the noon-midnight meridian and extended into the tail lobes. When viewed from the polar cap, this appears as a narrow finger of closed field lines extending into the polar cap. The plasma sheet thickening is caused by reconnection on the nightside magnetopause. This plasma sheet extension becomes less pronounced when the northward IMF enters the simulation box with the solar wind. For both cases the convection near midnight is toward the sun, and region-1-type field-aligned currents appear on both sides of the plasma sheet extension. For northward IMF the resulting magnetospheric configuration approached a quasi-steady state in which stable magnetospheric convection was maintained. The simulation results indicate that the presence of a northward B in the plasma sheet stabilizes the tail.
Le Chat, G.; Cohen, O.; Kasper, J. C.; Spangler, S. R.
2014-07-10
Polarized natural radio sources passing behind the Sun experience Faraday rotation as a consequence of the electron density and magnetic field strength in coronal plasma. Since Faraday rotation is proportional to the product of the density and the component of the magnetic field along the line of sight of the observer, a model is required to interpret the observations and infer coronal structures. Faraday rotation observations have been compared with relatively ad hoc models of the corona. Here for the first time we compare these observations with magnetohydrodynamic (MHD) models of the solar corona driven by measurements of the photospheric magnetic field. We use observations made with the NRAO Very Large Array of 34 polarized radio sources occulted by the solar corona between 5 and 14 solar radii. The measurements were made during 1997 May, and 2005 March and April. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona. We find that (1) using a synoptic map of the solar magnetic field just one Carrington rotation off produces poorer agreements, meaning that the outer corona changes in the course of one month, even in solar minimum; (2) global MHD models of the solar corona driven by photospheric magnetic field measurements are generally able to reproduce Faraday rotation observations; and (3) some sources show significant disagreement between the model and the observations, which appears to be a function of the proximity of the line of sight to the large-scale heliospheric current sheet.
Dynamic multiscaling in magnetohydrodynamic turbulence.
Ray, Samriddhi Sankar; Sahoo, Ganapati; Pandit, Rahul
2016-11-01
We present a study of the multiscaling of time-dependent velocity and magnetic-field structure functions in homogeneous, isotropic magnetohydrodynamic (MHD) turbulence in three dimensions. We generalize the formalism that has been developed for analogous studies of time-dependent structure functions in fluid turbulence to MHD. By carrying out detailed numerical studies of such time-dependent structure functions in a shell model for three-dimensional MHD turbulence, we obtain both equal-time and dynamic scaling exponents.
ERIC Educational Resources Information Center
Froschauer, Linda K.; Boudrot, Barbara
1986-01-01
Reviews the benefits and hazards that the sun provides. Describes activities which focus on the power of the sun and on the development of "Sun-sensible" behavior. Also included is a poster which contains puzzles and additional information and activities on safe sunning. (ML)
Data assimilation for magnetohydrodynamics systems
NASA Astrophysics Data System (ADS)
Mendoza, O. Barrero; de Moor, B.; Bernstein, D. S.
2006-05-01
Prediction of solar storms has become a very important issue due to the fact that they can affect dramatically the telecommunication and electrical power systems at the earth. As a result, a lot of research is being done in this direction, space weather forecast. Magnetohydrodynamics systems are being studied in order to analyse the space plasma dynamics, and techniques which have been broadly used in the prediction of earth environmental variables like the Kalman filter (KF), the ensemble Kalman filter (EnKF), the extended Kalman filter (EKF), etc., are being studied and adapted to this new framework. The assimilation of a wide range of space environment data into first-principles-based global numerical models will improve our understanding of the physics of the geospace environment and the forecasting of its behaviour. Therefore, the aim of this paper is to study the performance of nonlinear observers in magnetohydrodynamics systems, namely, the EnKF.The EnKF is based on a Monte Carlo simulation approach for propagation of process and measurement errors. In this paper, the EnKF for a nonlinear two-dimensional magnetohydrodynamic (2D-MHD) system is considered. For its implementation, two software packages are merged, namely, the Versatile Advection Code (VAC) written in Fortran and Matlab of Mathworks. The 2D-MHD is simulated with the VAC code while the EnKF is computed in Matlab. In order to study the performance of the EnKF in MHD systems, different number of measurement points as well as ensemble members are set.
Magnetohydrodynamic mechanism for pedestal formation.
Guazzotto, L; Betti, R
2011-09-16
Time-dependent two-dimensional magnetohydrodynamic simulations are carried out for tokamak plasmas with edge poloidal flow. Differently from conventional equilibrium theory, a density pedestal all around the edge is obtained when the poloidal velocity exceeds the poloidal sound speed. The outboard pedestal is induced by the transonic discontinuity, the inboard one by mass redistribution. The density pedestal follows the formation of a highly sheared flow at the transonic surface. These results may be relevant to the L-H transition and pedestal formation in high performance tokamak plasmas.
Method for manufacturing magnetohydrodynamic electrodes
Killpatrick, D.H.; Thresh, H.R.
1980-06-24
A method of manufacturing electrodes for use in a magnetohydrodynamic (MHD) generator is described comprising the steps of preparing a billet having a core of a first metal, a tubular sleeve of a second metal, and an outer sheath of an extrusile metal; evacuating the space between the parts of the assembled billet; extruding the billet; and removing the outer jacket. The extruded bar may be made into electrodes by cutting and bending to the shape required for an MHD channel frame. The method forms a bond between the first metal of the core and the second metal of the sleeve strong enough to withstand a hot and corrosive environment.
Action principle for relativistic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
D'Avignon, Eric; Morrison, P. J.; Pegoraro, F.
2015-04-01
A covariant action principle for ideal relativistic magnetohydrodynamics in terms of natural Eulerian field variables is given. This is done by generalizing the covariant Poisson bracket theory of Marsden et al. [Ann. Phys. 169, 29 (1986)], which uses a noncanonical bracket to effect constrained variations of an action functional. Various implications and extensions of this action principle are also discussed. Two significant byproducts of this formalism are the introduction of a new divergence-free 4-vector variable for the magnetic field, and a new Lie-dragged form for the theory.
Magneto-Hydrodynamics Based Microfluidics
Qian, Shizhi; Bau, Haim H.
2009-01-01
In microfluidic devices, it is necessary to propel samples and reagents from one part of the device to another, stir fluids, and detect the presence of chemical and biological targets. Given the small size of these devices, the above tasks are far from trivial. Magnetohydrodynamics (MHD) offers an elegant means to control fluid flow in microdevices without a need for mechanical components. In this paper, we review the theory of MHD for low conductivity fluids and describe various applications of MHD such as fluid pumping, flow control in fluidic networks, fluid stirring and mixing, circular liquid chromatography, thermal reactors, and microcoolers. PMID:20046890
Sun and Sun Worship in Different Cultures
NASA Astrophysics Data System (ADS)
Farmanyan, S. V.; Mickaelian, A. M.
2014-10-01
The Sun symbol is found in many cultures throughout history, it has played an important role in shaping our life on Earth since the dawn of time. Since the beginning of human existence, civilisations have established religious beliefs that involved the Sun's significance to some extent. As new civilisations and religions developed, many spiritual beliefs were based on those from the past so that there has been an evolution of the Sun's significance throughout cultural development. For comparing and finding the origin of the Sun we made a table of 66 languages and compared the roots of the words. For finding out from where these roots came from, we also made a table of 21 Sun Gods and Goddesses and proved the direct crossing of language and mythology.
Variational integrators for reduced magnetohydrodynamics
Kraus, Michael; Tassi, Emanuele; Grasso, Daniela
2016-09-15
Reduced magnetohydrodynamics is a simplified set of magnetohydrodynamics equations with applications to both fusion and astrophysical plasmas, possessing a noncanonical Hamiltonian structure and consequently a number of conserved functionals. We propose a new discretisation strategy for these equations based on a discrete variational principle applied to a formal Lagrangian. The resulting integrator preserves important quantities like the total energy, magnetic helicity and cross helicity exactly (up to machine precision). As the integrator is free of numerical resistivity, spurious reconnection along current sheets is absent in the ideal case. If effects of electron inertia are added, reconnection of magnetic field lines is allowed, although the resulting model still possesses a noncanonical Hamiltonian structure. After reviewing the conservation laws of the model equations, the adopted variational principle with the related conservation laws is described both at the continuous and discrete level. We verify the favourable properties of the variational integrator in particular with respect to the preservation of the invariants of the models under consideration and compare with results from the literature and those of a pseudo-spectral code.
Variational integrators for reduced magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Kraus, Michael; Tassi, Emanuele; Grasso, Daniela
2016-09-01
Reduced magnetohydrodynamics is a simplified set of magnetohydrodynamics equations with applications to both fusion and astrophysical plasmas, possessing a noncanonical Hamiltonian structure and consequently a number of conserved functionals. We propose a new discretisation strategy for these equations based on a discrete variational principle applied to a formal Lagrangian. The resulting integrator preserves important quantities like the total energy, magnetic helicity and cross helicity exactly (up to machine precision). As the integrator is free of numerical resistivity, spurious reconnection along current sheets is absent in the ideal case. If effects of electron inertia are added, reconnection of magnetic field lines is allowed, although the resulting model still possesses a noncanonical Hamiltonian structure. After reviewing the conservation laws of the model equations, the adopted variational principle with the related conservation laws is described both at the continuous and discrete level. We verify the favourable properties of the variational integrator in particular with respect to the preservation of the invariants of the models under consideration and compare with results from the literature and those of a pseudo-spectral code.
ERIC Educational Resources Information Center
Sutley, Jane
2010-01-01
This article presents an art project designed for upper-elementary students to (1) imagine visual differences in the sun's appearance during the four seasons; (2) develop ideas for visually translating their personal experiences regarding the seasons to their sun drawings; (3) create four distinctive seasonal suns using colors and imagery to…
ERIC Educational Resources Information Center
Stark, Meri-Lyn
2005-01-01
Understanding the Sun has challenged people since ancient times. Mythology from the Greek, Inuit, and Inca cultures attempted to explain the daily appearance and nightly disappearance of the Sun by relating it to a chariot being chased across the sky. While people no longer believe the Sun is a chariot racing across the sky, teachers are still…
This movie shows fireworks on the sun as 10 significant flares erupted on the sun from Oct. 19-28, 2014. The graph shows X-ray output from the sun as measured by NOAA’s GOES spacecraft. The X-rays ...
NASA Technical Reports Server (NTRS)
Antiochos, Spiro K.
2009-01-01
A fundamental property of the Sun's corona is that it is violently dynamic. The most spectacular and most energetic manifestations of this activity are the giant magnetic disruptions that give rise to coronal mass ejections (CME) and eruptive flares. These major events are of critical importance, because they drive the most destructive forms of space weather at Earth and in the solar system, and they provide a unique opportunity to study, in revealing detail, the interaction of magnetic field and matter, in particular, magnetohydrodynamic instability and nonequilibrium - processes that are at the heart of laboratory and astrophysical plasma physics. Recent observations by a number of NASA space missions have given us new insights into the physical mechanisms that underlie coronal explosions. Furthermore, massively-parallel computations have now allowed us to calculate fully three-dimensional models for the Sun's activity. In this talk I will review some of the latest observations of the Sun, including those from the just-launched Hinode and STEREO mission, and discuss recent advances in the theory and modeling of explosive solar activity.
Numerical Investigations of Magnetohydrodynamic Turbulence
NASA Astrophysics Data System (ADS)
Mueller, W. C.
2006-12-01
Incompressible magnetohydrodynamic turbulence studied by large-scale direct numerical simulations has revealed a number of new interesting facets. The Goldreich-Sridhar phenomenology partly breaks down in turbulence subject to a strong mean magnetic field. This leads to a measureable anisotropy of two-point statistics. The nonlinear dynamics of kinetic (E^K) and magnetic energy (E^M) is the result of a dynamical equilibrium of Alfvén effect and a small-sale dynamo leading to a scaling relation between total and residual energy: (E^M-E^K)~ k(E^K+E^M)2. The probability density functions of cascading quantities are found to exhibit mono-scaling.
Method for manufacturing magnetohydrodynamic electrodes
Killpatrick, Don H.; Thresh, Henry R.
1982-01-01
A method of manufacturing electrodes for use in a magnetohydrodynamic (MHD) generator comprising the steps of preparing a billet having a core 10 of a first metal, a tubular sleeve 12 of a second metal, and an outer sheath 14, 16, 18 of an extrusile metal; evacuating the space between the parts of the assembled billet; extruding the billet; and removing the outer jacket 14. The extruded bar may be made into electrodes by cutting and bending to the shape required for an MDH channel frame. The method forms a bond between the first metal of the core 10 and the second metal of the sleeve 12 strong enough to withstand a hot and corrosive environment.
Magnetohydrodynamic production of relativistic jets.
Meier, D L; Koide, S; Uchida, Y
2001-01-05
A number of astronomical systems have been discovered that generate collimated flows of plasma with velocities close to the speed of light. In all cases, the central object is probably a neutron star or black hole and is either accreting material from other stars or is in the initial violent stages of formation. Supercomputer simulations of the production of relativistic jets have been based on a magnetohydrodynamic model, in which differential rotation in the system creates a magnetic coil that simultaneously expels and pinches some of the infalling material. The model may explain the basic features of observed jets, including their speed and amount of collimation, and some of the details in the behavior and statistics of different jet-producing sources.
Magnetohydrodynamic turbulence: Observation and experiment
Brown, M. R.; Schaffner, D. A.; Weck, P. J.
2015-05-15
We provide a tutorial on the paradigms and tools of magnetohydrodynamic (MHD) turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuations E{sub B}(f). We will describe five useful statistical tools for MHD turbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHD fluctuations in the solar wind. A single dataset from the Wind satellite will be used to illustrate all five temporal statistical tools.
Micromachined magnetohydrodynamic actuators and sensors
Lee, Abraham P.; Lemoff, Asuncion V.
2000-01-01
A magnetohydrodynamic (MHD) micropump and microsensor which utilizes micromachining to integrate the electrodes with microchannels and includes a magnet for producing magnetic fields perpendicular to both the electrical current direction and the fluid flow direction. The magnet can also be micromachined and integrated with the micropump using existing technology. The MHD micropump, for example, can generate continuous, reversible flow, with readily controllable flow rates. The flow can be reversed by either reversing the electrical current flow or reversing the magnetic field. By mismatching the electrodes, a swirling vortex flow can be generated for potential mixing applications. No moving parts are necessary and the dead volume is minimal. The micropumps can be placed at any position in a fluidic circuit and a combination of micropumps can generate fluidic plugs and valves.
ANISOTROPIC INTERMITTENCY OF MAGNETOHYDRODYNAMIC TURBULENCE
Osman, K. T.; Kiyani, K. H.; Chapman, S. C.; Hnat, B.
2014-03-10
A higher-order multiscale analysis of spatial anisotropy in inertial range magnetohydrodynamic turbulence is presented using measurements from the STEREO spacecraft in fast ambient solar wind. We show for the first time that, when measuring parallel to the local magnetic field direction, the full statistical signature of the magnetic and Elsässer field fluctuations is that of a non-Gaussian globally scale-invariant process. This is distinct from the classic multiexponent statistics observed when the local magnetic field is perpendicular to the flow direction. These observations are interpreted as evidence for the weakness, or absence, of a parallel magnetofluid turbulence energy cascade. As such, these results present strong observational constraints on the statistical nature of intermittency in turbulent plasmas.
Relativistic magnetohydrodynamics in one dimension
NASA Astrophysics Data System (ADS)
Lyutikov, Maxim; Hadden, Samuel
2012-02-01
We derive a number of solutions for one-dimensional dynamics of relativistic magnetized plasma that can be used as benchmark estimates in relativistic hydrodynamic and magnetohydrodynamic numerical codes. First, we analyze the properties of simple waves of fast modes propagating orthogonally to the magnetic field in relativistically hot plasma. The magnetic and kinetic pressures obey different equations of state, so that the system behaves as a mixture of gases with different polytropic indices. We find the self-similar solutions for the expansion of hot strongly magnetized plasma into vacuum. Second, we derive linear hodograph and Darboux equations for the relativistic Khalatnikov potential, which describe arbitrary one-dimensional isentropic relativistic motion of cold magnetized plasma and find their general and particular solutions. The obtained hodograph and Darboux equations are very powerful: A system of highly nonlinear, relativistic, time-dependent equations describing arbitrary (not necessarily self-similar) dynamics of highly magnetized plasma reduces to a single linear differential equation.
Relativistic magnetohydrodynamics in one dimension.
Lyutikov, Maxim; Hadden, Samuel
2012-02-01
We derive a number of solutions for one-dimensional dynamics of relativistic magnetized plasma that can be used as benchmark estimates in relativistic hydrodynamic and magnetohydrodynamic numerical codes. First, we analyze the properties of simple waves of fast modes propagating orthogonally to the magnetic field in relativistically hot plasma. The magnetic and kinetic pressures obey different equations of state, so that the system behaves as a mixture of gases with different polytropic indices. We find the self-similar solutions for the expansion of hot strongly magnetized plasma into vacuum. Second, we derive linear hodograph and Darboux equations for the relativistic Khalatnikov potential, which describe arbitrary one-dimensional isentropic relativistic motion of cold magnetized plasma and find their general and particular solutions. The obtained hodograph and Darboux equations are very powerful: A system of highly nonlinear, relativistic, time-dependent equations describing arbitrary (not necessarily self-similar) dynamics of highly magnetized plasma reduces to a single linear differential equation.
Magnetohydrodynamic Turbulence and the Geodynamo
NASA Technical Reports Server (NTRS)
Shebalin, John V.
2016-01-01
Recent research results concerning forced, dissipative, rotating magnetohydrodynamic (MHD) turbulence will be discussed. In particular, we present new results from long-time Fourier method (periodic box) simulations in which forcing contains varying amounts of magnetic and kinetic helicity. Numerical results indicate that if MHD turbulence is forced so as to produce a state of relatively constant energy, then the largest-scale components are dominant and quasistationary, and in fact, have an effective dipole moment vector that aligns closely with the rotation axis. The relationship of this work to established results in ideal MHD turbulence, as well as to models of MHD turbulence in a spherical shell will also be presented. These results appear to be very pertinent to understanding the Geodynamo and the origin of its dominant dipole component. Our conclusion is that MHD turbulence, per se, may well contain the origin of the Earth's dipole magnetic field.
Magnetohydrodynamic turbulence: Observation and experimenta)
NASA Astrophysics Data System (ADS)
Brown, M. R.; Schaffner, D. A.; Weck, P. J.
2015-05-01
We provide a tutorial on the paradigms and tools of magnetohydrodynamic (MHD) turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuations EB(f ) . We will describe five useful statistical tools for MHD turbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHD fluctuations in the solar wind. A single dataset from the Wind satellite will be used to illustrate all five temporal statistical tools.
Weakly nonlinear magnetohydrodynamic wave interactions
Webb, G.M.; Brio, M.; Kruse, M.T.; Zank, G.P.
1999-06-01
Equations describing weakly nonlinear magnetohydrodynamic (MHD) wave interactions in one Cartesian space dimension are discussed. For wave propagation in uniform media, the wave interactions of interest consist of: (a) three-wave resonant interactions in which high frequency waves, may evolve on long space and time scales if the wave phases satisfy the resonance conditions; (b) Burgers self-wave steepening for the magnetoacoustic waves, and (c) mean wave field effects, in which a particular wave interacts with the mean wave field of the other waves. For wave propagation in non-uniform media, further linear wave mixing terms appear in the equations. The equations describe four types of resonant triads: slow-fast magnetosonic wave interaction; Alfv{acute e}n-entropy wave interaction; Alfv{acute e}n-magnetosonic wave interaction; and magnetosonic-entropy wave interaction. The formalism is restricted to coherent wave interactions. {copyright} {ital 1999 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Raphaldini, Breno; Raupp, Carlos F. M.
2015-01-01
The solar dynamo is known to be associated with several periodicities, with the nearly 11/22 yr cycle being the most pronounced one. Even though these quasiperiodic variations of solar activity have been attributed to the underlying dynamo action in the Sun's interior, a fundamental theoretical description of these cycles is still elusive. Here, we present a new possible direction in understanding the Sun's cycles based on resonant nonlinear interactions among magnetohydrodynamic (MHD) Rossby waves. The WKB theory for dispersive waves is applied to magnetohydrodynamic shallow-water equations describing the dynamics of the solar tachocline, and the reduced dynamics of a resonant triad composed of MHD Rossby waves embedded in constant toroidal magnetic field is analyzed. In the conservative case, the wave amplitudes evolve periodically in time, with periods on the order of the dominant solar activity timescale (~11 yr). In addition, the presence of linear forcings representative of either convection or instabilities of meridionally varying background states appears to be crucial in balancing dissipation and thus sustaining the periodic oscillations of wave amplitudes associated with resonant triad interactions. Examination of the linear theory of MHD Rossby waves embedded in a latitudinally varying mean flow demonstrates that MHD Rossby waves propagate toward the equator in a waveguide from -35° to 35° in latitude, showing a remarkable resemblance to the structure of the butterfly diagram of the solar activity. Therefore, we argue that resonant nonlinear magnetohydrodynamic Rossby wave interactions might significantly contribute to the observed cycles of magnetic solar activity.
Wysor, Robert Wesley
2005-09-14
The ORNL Sun Tracker software is the user interface that operates on a Personal Computer and serially communicates with the controller board. This software allows the user to manually operate the Hybrid Solar Lighting (HSL) unit. It displays the current location of the HSL unit, its parameters and it provides real-time monitoring. The ORNL Sun Tracker software is also the main component used in setting up and calibrating the tracker. It contains a setup screen that requires latitude, longitude, and a few other key values to accurately locate the sun's position. The software also will provide the user access to calibrate the tracking location in relation to the sun's actual position.
Magnetohydrodynamic Shocks in the Interplanetary Space: a Theoretical Review
NASA Astrophysics Data System (ADS)
Oliveira, D. M.
2017-02-01
I discuss in this brief review some properties of magnetohydrodynamic (MHD) discontinuities in the interplanetary space. My emphasis is on a special case of MHD discontinuity, namely interplanetary (IP) shocks, and those that are found at 1 AU. I derive the Rankine-Hugoniot (RH) equations to evaluate plasma parameters in the downstream region (shocked plasma) in relation to the upstream region (unshocked plasma). These properties are used to classify IP shocks in terms of their geometry and their direction of propagation in relation to the Sun. The shock geometry is determined in terms of two angles: θ _{Bn}, the angle between the upstream magnetic field and the shock normal, and θ _{xn}, the angle between the shock normal and the Sun-Earth line. Sources of IP shocks frequently found in the solar wind at Earth's orbit are presented. Then the RH equations are solved for two categories of IP shocks in a special case: perpendicular shocks, when θ _{Bn} is 90 ∘, and oblique shocks, when that angle is 45 ∘. Finally, I highlight the importance of knowing the shock geometry, mainly the impact angle θ _{xn}, specially whether the shock is frontal or inclined, for space weather-related investigations. IP shocks are known to be more geoeffective if they strike the Earth's magnetosphere frontally, or with impact angle nearly null. These results have been reported both by modeling and experimental studies in the literature.
Computational Methods for Ideal Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Kercher, Andrew D.
Numerical schemes for the ideal magnetohydrodynamics (MHD) are widely used for modeling space weather and astrophysical flows. They are designed to resolve the different waves that propagate through a magnetohydro fluid, namely, the fast, Alfven, slow, and entropy waves. Numerical schemes for ideal magnetohydrodynamics that are based on the standard finite volume (FV) discretization exhibit pseudo-convergence in which non-regular waves no longer exist only after heavy grid refinement. A method is described for obtaining solutions for coplanar and near coplanar cases that consist of only regular waves, independent of grid refinement. The method, referred to as Compound Wave Modification (CWM), involves removing the flux associated with non-regular structures and can be used for simulations in two- and three-dimensions because it does not require explicitly tracking an Alfven wave. For a near coplanar case, and for grids with 213 points or less, we find root-mean-square-errors (RMSEs) that are as much as 6 times smaller. For the coplanar case, in which non-regular structures will exist at all levels of grid refinement for standard FV schemes, the RMSE is as much as 25 times smaller. A multidimensional ideal MHD code has been implemented for simulations on graphics processing units (GPUs). Performance measurements were conducted for both the NVIDIA GeForce GTX Titan and Intel Xeon E5645 processor. The GPU is shown to perform one to two orders of magnitude greater than the CPU when using a single core, and two to three times greater than when run in parallel with OpenMP. Performance comparisons are made for two methods of storing data on the GPU. The first approach stores data as an Array of Structures (AoS), e.g., a point coordinate array of size 3 x n is iterated over. The second approach stores data as a Structure of Arrays (SoA), e.g. three separate arrays of size n are iterated over simultaneously. For an AoS, coalescing does not occur, reducing memory efficiency
ERIC Educational Resources Information Center
Collins, Margaret
1998-01-01
Describes sessions in two schools that focused on recent work with 2,857 children in Europe researching the children's perceptions of sun on skin. Investigates children's ideas about skin on different parts of the body, which was most vulnerable to the sun, and different types and colors. (Author/CCM)
Magnetohydrodynamic Propulsion for the Classroom
NASA Astrophysics Data System (ADS)
Font, Gabriel I.; Dudley, Scott C.
2004-10-01
The cinema industry can sometimes prove to be an ally when searching for material with which to motivate students to learn physics. Consider, for example, the electromagnetic force on a current in the presence of a magnetic field. This phenomenon is at the heart of magnetohydrodynamic (MHD) propulsion systems. A submarine employing this type of propulsion was immortalized in the movie Hunt for Red October. While mentioning this to students certainly gets their attention, it often elicits comments that it is only fiction and not physically possible. Imagine their surprise when a working system is demonstrated! It is neither difficult nor expensive to construct a working system that can be demonstrated in the front of a classroom.2 In addition, all aspects of the engineering hurdles that must be surmounted and myths concerning this "silent propulsion" system are borne out in a simple apparatus. This paper details how to construct an inexpensive MHD propulsion boat that can be demonstrated for students in the classroom.
Magnetohydrodynamic (MHD) driven droplet mixer
Lee, Abraham P.; Lemoff, Asuncion V.; Miles, Robin R.
2004-05-11
A magnetohydrodynamic fluidic system mixes a first substance and a second substance. A first substrate section includes a first flow channel and a first plurality of pairs of spaced electrodes operatively connected to the first flow channel. A second substrate section includes a second flow channel and a second plurality of pairs of spaced electrodes operatively connected to the second flow channel. A third substrate section includes a third flow channel and a third plurality of pairs of spaced electrodes operatively connected to the third flow channel. A magnetic section and a control section are operatively connected to the spaced electrodes. The first substrate section, the second substrate section, the third substrate section, the first plurality of pairs of spaced electrodes, the second plurality of pairs of spaced electrodes, the third plurality of pairs of spaced electrodes, the magnetic section, and the control section are operated to move the first substance through the first flow channel, the second substance through the second flow channel, and both the first substance and the second substance into the third flow channel where they are mixed.
Shell models of magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Plunian, Franck; Stepanov, Rodion; Frick, Peter
2013-02-01
Shell models of hydrodynamic turbulence originated in the seventies. Their main aim was to describe the statistics of homogeneous and isotropic turbulence in spectral space, using a simple set of ordinary differential equations. In the eighties, shell models of magnetohydrodynamic (MHD) turbulence emerged based on the same principles as their hydrodynamic counter-part but also incorporating interactions between magnetic and velocity fields. In recent years, significant improvements have been made such as the inclusion of non-local interactions and appropriate definitions for helicities. Though shell models cannot account for the spatial complexity of MHD turbulence, their dynamics are not over simplified and do reflect those of real MHD turbulence including intermittency or chaotic reversals of large-scale modes. Furthermore, these models use realistic values for dimensionless parameters (high kinetic and magnetic Reynolds numbers, low or high magnetic Prandtl number) allowing extended inertial range and accurate dissipation rate. Using modern computers it is difficult to attain an inertial range of three decades with direct numerical simulations, whereas eight are possible using shell models. In this review we set up a general mathematical framework allowing the description of any MHD shell model. The variety of the latter, with their advantages and weaknesses, is introduced. Finally we consider a number of applications, dealing with free-decaying MHD turbulence, dynamo action, Alfvén waves and the Hall effect.
Magnetohydrodynamic Simulations of Barred Galaxies
NASA Astrophysics Data System (ADS)
Kim, W.-T.
2013-04-01
Magnetic fields are pervasive in barred galaxies, especially in gaseous substructures such as dust lanes and nuclear rings. To explore the effects of magnetic fields on the formation of the substructures as well as on the mass inflow rates to the galaxy center, we run two-dimensional, ideal magnetohydrodynamic simulations. We use a modified version of the Athena code whose numerical magnetic diffusivity is shown to be of third order in space. In the bar regions, magnetic fields are compressed and abruptly bent around the dust-lane shocks. The associated magnetic stress not only reduces the peak density of the dust-lane shocks but also removes angular momentum further from the gas that is moving radially in. Nuclear rings that form at the location of centrifugal barrier rather than resonance with the bar are smaller and more radially distributed, and the mass flow rate to the galaxy center is correspondingly larger in models with stronger magnetic fields. Outside the bar regions, the bar potential and strong shear conspire to amplify the field strength near the corotation resonance. The amplified fields transport angular momentum outward, producing trailing magnetic arms with strong fields and low density. The base of the magnetic arms are found to be unstable to a tearing-mode instability of magnetic reconnection. This produces numerous magnetic islands that eventually make the outer regions highly chaotic.
Harrison, Richard A
2008-05-28
The nature of our star, the Sun, is dominated by its complex and variable magnetic fields. It is the purpose of this paper to review the fundamental nature of our magnetic Sun by outlining the most basic principles behind the way the Sun works and how its fields are generated, and to examine not only the historical observations of our magnetic star, but, in particular, to study the wonderful observations of the Sun being made from space today. However, lying behind all of this are the most basic equations derived by James Clerk Maxwell, describing how the magnetic fields and plasmas of our Sun's atmosphere, and indeed of all stellar atmospheres, work and how they influence the Earth.
JET FORMATION FROM MASSIVE YOUNG STARS: MAGNETOHYDRODYNAMICS VERSUS RADIATION PRESSURE
Vaidya, Bhargav; Porth, Oliver; Fendt, Christian; Beuther, Henrik E-mail: fendt@mpia.de
2011-11-20
Observations indicate that outflows from massive young stars are more collimated during their early evolution compared to later stages. Our paper investigates various physical processes that impact the outflow dynamics, i.e., its acceleration and collimation. We perform axisymmetric magnetohydrodynamic (MHD) simulations particularly considering the radiation pressure exerted by the star and the disk. We have modified the PLUTO code to include radiative forces in the line-driving approximation. We launch the outflow from the innermost disk region (r < 50 AU) by magnetocentrifugal acceleration. In order to disentangle MHD effects from radiative forces, we start the simulation in pure MHD and later switch on the radiation force. We perform a parameter study considering different stellar masses (thus luminosity), magnetic flux, and line-force strength. For our reference simulation-assuming a 30 M{sub Sun} star-we find substantial de-collimation of 35% due to radiation forces. The opening angle increases from 20 Degree-Sign to 32 Degree-Sign for stellar masses from 20 M{sub Sun} to 60 M{sub Sun }. A small change in the line-force parameter {alpha} from 0.60 to 0.55 changes the opening angle by {approx}8 Degree-Sign . We find that it is mainly the stellar radiation that affects the jet dynamics. Unless the disk extends very close to the star, its force is too small to have much impact. Essentially, our parameter runs with different stellar masses can be understood as a proxy for the time evolution of the star-outflow system. Thus, we have shown that when the stellar mass (thus luminosity) increases with age, the outflows become less collimated.
NASA Astrophysics Data System (ADS)
Thieman, J.; Ng, C.; Lewis, E.; Cline, T.
2010-08-01
Sun-Earth Day is a well-coordinated series of programs, resources and events under a unique yearly theme highlighting the fundamentals of heliophysics research and missions. A menu of activities, conducted throughout the year, inspire and educate participants. Sun-Earth Day itself can vary in date, but usually is identified by a celebration on or near the spring equinox. Through the Sun-Earth Day framework we have been able to offer a series of coordinated events that promote and highlight the Sun, its connection to Earth and the other planets. Sun-Earth Day events are hosted by educators, museums, amateur astronomers and scientists and occur at schools, community groups, parks, planetaria and science centers around the globe. Sun-Earth Day raises the awareness and knowledge of formal and informal education audiences concerning space weather and heliophysics. By building on the success of Sun-Earth Day yearly celebrations, we seek to affect people of all backgrounds and ages with the wonders of heliophysics science, discovery, and exploration in ways that are both tangible and meaningful to their lives.
From the Einstein-Szilard Patent to Modern Magnetohydrodynamics.
ERIC Educational Resources Information Center
Povh, I. L.; Barinberg, A. D.
1979-01-01
Examines present-day and future prospects of the applications of modern magnetohydrodynamics in a number of countries. Explains how the electromagnetic pump, which was invented by Einstein and Leo Szilard, led to the development of applied magnetohydrodynamics. (HM)
Accurate, meshless methods for magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Hopkins, Philip F.; Raives, Matthias J.
2016-01-01
Recently, we explored new meshless finite-volume Lagrangian methods for hydrodynamics: the `meshless finite mass' (MFM) and `meshless finite volume' (MFV) methods; these capture advantages of both smoothed particle hydrodynamics (SPH) and adaptive mesh refinement (AMR) schemes. We extend these to include ideal magnetohydrodynamics (MHD). The MHD equations are second-order consistent and conservative. We augment these with a divergence-cleaning scheme, which maintains nabla \\cdot B≈ 0. We implement these in the code GIZMO, together with state-of-the-art SPH MHD. We consider a large test suite, and show that on all problems the new methods are competitive with AMR using constrained transport (CT) to ensure nabla \\cdot B=0. They correctly capture the growth/structure of the magnetorotational instability, MHD turbulence, and launching of magnetic jets, in some cases converging more rapidly than state-of-the-art AMR. Compared to SPH, the MFM/MFV methods exhibit convergence at fixed neighbour number, sharp shock-capturing, and dramatically reduced noise, divergence errors, and diffusion. Still, `modern' SPH can handle most test problems, at the cost of larger kernels and `by hand' adjustment of artificial diffusion. Compared to non-moving meshes, the new methods exhibit enhanced `grid noise' but reduced advection errors and diffusion, easily include self-gravity, and feature velocity-independent errors and superior angular momentum conservation. They converge more slowly on some problems (smooth, slow-moving flows), but more rapidly on others (involving advection/rotation). In all cases, we show divergence control beyond the Powell 8-wave approach is necessary, or all methods can converge to unphysical answers even at high resolution.
Electron magnetohydrodynamics: Dynamics and turbulence
NASA Astrophysics Data System (ADS)
Lyutikov, Maxim
2013-11-01
We consider dynamics and turbulent interaction of whistler modes within the framework of inertialess electron magnetohydrodynamics (EMHD). We argue that there is no energy principle in EMHD: any stationary closed configuration is neutrally stable. On the other hand, the relaxation principle, the long term evolution of a weakly dissipative system towards Taylor-Beltrami state, remains valid in EMHD. We consider the turbulent cascade of whistler modes. We show that (i) harmonic whistlers are exact nonlinear solutions; (ii) collinear whistlers do not interact (including counterpropagating); (iii) waves with the same value of the wave vector k1=k2 do not interact; (iv) whistler modes have a dispersion that allows a three-wave decay, including into a zero frequency mode; (v) the three-wave interaction effectively couples modes with highly different wave numbers and propagation angles. In addition, linear interaction of a whistler with a single zero mode can lead to spatially divergent structures via parametric instability. All these properties are drastically different from MHD, so that the qualitative properties of the Alfvén turbulence can not be transferred to the EMHD turbulence. We derive the Hamiltonian formulation of EMHD, and using Bogoliubov transformation reduce it to the canonical form; we calculate the matrix elements for the three-wave interaction of whistlers. We solve numerically the kinetic equation and show that, generally, the EMHD cascade develops within a broad range of angles, while transiently it may show anisotropic, nearly two-dimensional structures. Development of a cascade depends on the forcing (nonuniversal) and often fails to reach a steady state. Analytical estimates predict the spectrum of magnetic fluctuations for the quasi-isotropic cascade ∝k-2. The cascade remains weak (not critically balanced). The cascade is UV local, while the infrared locality is weakly (logarithmically) violated.
1998-09-30
Sounding the Sun Antony Fraser-Smith STAR Laboratory Stanford University Stanford, CA 94305 phone: (650) 723-3684 fax: (650) 723-9251 email...TITLE AND SUBTITLE Sounding the Sun 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK...systems. The objective of our “Sounding the sun ” experiment is to detect earth-directed CME’s by using existing earth-based HF (3- 30 MHz) radar systems
Variational Integrators for Ideal and Reduced Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Kraus, Michael; Maj, Omar; Tassi, Emanuele; Grasso, Daniela
2016-10-01
Ideal and reduced magnetohydrodynamics are simplified sets of magnetohydrodynamics equations with applications to both fusion and astrophysical plasmas, possessing a noncanonical Hamiltonian structure and a number of conserved functionals. We propose a new discretisation strategy for these equations based on a discrete variational principle applied to a formal Lagrangian. Discrete exterior calculus is used for the discretisation of the field variables in order to preserve their geometrical character. The resulting integrators preserve important quantities like the total energy, magnetic helicity and cross helicity exactly (up to machine precision). As these integrators are free of numerical resistivity, the magnetic field line topology is preserved and spurious reconnection is absent in the ideal case. Only when effects of finite electron mass are added, magnetic reconnection takes place. The excellent conservation properties of the methods are exemplified with numerical examples in 2D. We conclude with an outlook towards the treatment of general geometries in 3D and full magnetohydrodynamics.
ERIC Educational Resources Information Center
Lindsay, Sally, Ed.
1976-01-01
Six articles review current understanding and research in solar physics. Included are topics on sunspots, the corona, solar flares, solar waves, and solar-energy generation. Also included is a resume of physical data relating to the sun. (SL)
For the past 4 years, the two STEREO spacecraft have been moving away from Earth and gaining a more complete picture of the sun. On Feb. 6, 2011, NASA will reveal the first ever images of the entir...
... in combination with wide-brimmed hats, sunglasses, and sunscreen, are all helpful in preventing damage to the ... Any one of these by itself, even the sunscreen, may not be enough to prevent sun damage.
SDO watched as an active region in the Sunâs southern hemisphere produced a whole series of looping arcs of plasma in profile (Sept. 11-13, 2010). The arcs are actually charged particles spirali...
Nicholeen Viall, a solar scientist at NASA's Goddard Space Flight Center creates images of the sun reminiscent of Van Gogh, but it's science, not art. The color of each pixel contains a wealth of i...
New approach to nonrelativistic ideal magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Banerjee, Rabin; Kumar, Kuldeep
2016-07-01
We provide a novel action principle for nonrelativistic ideal magnetohydrodynamics in the Eulerian scheme exploiting a Clebsch-type parametrisation. Both Lagrangian and Hamiltonian formulations have been considered. Within the Hamiltonian framework, two complementary approaches have been discussed using Dirac's constraint analysis. In one case the Hamiltonian is canonical involving only physical variables but the brackets have a noncanonical structure, while the other retains the canonical structure of brackets by enlarging the phase space. The special case of incompressible magnetohydrodynamics is also considered where, again, both the approaches are discussed in the Hamiltonian framework. The conservation of the stress tensor reveals interesting aspects of the theory.
NASA Technical Reports Server (NTRS)
Gopalswamy, Natchimuthuk
2012-01-01
Thus the Sun forms the basis for life on Earth via the black body radiation it emits. The Sun also emits mass in the form of the solar wind and the coronal mass ejections (CMEs). Mass emission also occurs in the form of solar energetic particles (SEPs), which happens during CMEs and solar flares. Both the mass and electromagnetic energy output of the Sun vary over a wide range of time scales, thus introducing disturbances on the space environment that extends from the Sun through the entire heliosphere including the magnetospheres and ionospheres of planets and moons of the solar system. Although our habitat is located in the neutral atmosphere of Earth, we are intimately connected to the non-neutral space environment starting from the ionosphere to the magnetosphere and to the vast interplanetary space. The variability of the solar mass emissions results in the interaction between the solar wind plasma and the magnetospheric plasma leading to huge disturbances in the geospace. The Sun ionizes our atmosphere and creates the ionosphere. The ionosphere can be severely disturbed by the transient energy input from solar flares and the solar wind during geomagnetic storms. The complex interplay between Earth's magnetic field and the solar magnetic field carried by the solar wind presents varying conditions that are both beneficial and hazardous to life on earth. This seminar presents some of the key aspects of this Sun-Earth connection that we have learned since the birth of space science as a scientific discipline some half a century ago.
On energy conservation in extended magnetohydrodynamics
Kimura, Keiji; Morrison, P. J.
2014-08-15
A systematic study of energy conservation for extended magnetohydrodynamic models that include Hall terms and electron inertia is performed. It is observed that commonly used models do not conserve energy in the ideal limit, i.e., when viscosity and resistivity are neglected. In particular, a term in the momentum equation that is often neglected is seen to be needed for conservation of energy.
Solar-driven liquid metal magnetohydrodynamic generator
NASA Technical Reports Server (NTRS)
Lee, J. H.; Hohl, F.
1981-01-01
A solar oven heated by concentrated solar radiation as the heat source of a liquid metal magnetohydrodynamic (LMMHD) power generation system is proposed. The design allows the production of electric power in space, as well as on Earth, at high rates of efficiency. Two types of the solar oven suitable for the system are discussed.
Potential vorticity formulation of compressible magnetohydrodynamics.
Arter, Wayne
2013-01-04
Compressible ideal magnetohydrodynamics is formulated in terms of the time evolution of potential vorticity and magnetic flux per unit mass using a compact Lie bracket notation. It is demonstrated that this simplifies analytic solution in at least one very important situation relevant to magnetic fusion experiments. Potentially important implications for analytic and numerical modelling of both laboratory and astrophysical plasmas are also discussed.
Physical consistency in modeling interplanetary magnetohydrodynamic fluctuations
NASA Technical Reports Server (NTRS)
Zhou, Y.; Matthaeus, W. H.; Roberts, D. A.; Goldstein, M. L.
1990-01-01
The validity of the Velli, Grappin and Mangeney (1989) model is evaluated. It is argued that the model is incorrect because it mixes different dynamical models, assumes weak nonlinearities, makes predictions that vary with observations, and violates causality. It is proposed that self-similar behavior in the coronal source region of the magnetohydrodynamic fluctuations cause the Kolmogorov-like spectra.
Global Magnetohydrodynamic Modeling of the Solar Corona
NASA Technical Reports Server (NTRS)
Linker, Jon A.
2001-01-01
This report describes the progress made in the investigation of the solar corona using magnetohydrodynamic (MHD) simulations. Coronal mass ejections (CME) are believed to be the primary cause of nonrecurrent geomagnetic storms and these have been investigated through the use of three-dimensional computer simulation.
NASA Technical Reports Server (NTRS)
2006-01-01
Parallax gives depth to life. Simultaneous viewing from slightly different vantage points makes binocular humans superior to monocular cyclopes, and fixes us in the third dimension of the Universe. We've been stunned by 3-d images of Venus and Mars (along with more familiar views of earth). Now astronomers plan to give us the best view of all, 3-d images of the dynamic Sun. That's one of the prime goals of NASA's Solar Terrestrial Relations Observatories, also known as STEREO. STEREO is a pair of spacecraft observatories, one placed in orbit in front of earth, and one to be placed in an earth-trailing orbit. Simultaneous observations of the Sun with the two STEREO spacecraft will provide extraordinary 3-d views of all types of solar activity, especially the dramatic events called coronal mass ejections which send high energy particles from the outer solar atmosphere hurtling towards earth. The image above the first image of the sun by the two STEREO spacecraft, an extreme ultraviolet shot of the Sun's million-degree corona, taken by the Extreme Ultraviolet Imager on the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument package. STEREO's first 3-d solar images should be available in April if all goes well. Put on your red and blue glasses!
The magnetohydrodynamics of current sheets
NASA Technical Reports Server (NTRS)
Priest, E. R.
1985-01-01
Examples of current sheets are summarized and their formation is described. A universal phenomenon in cosmic plasmas is the creation of sheets off intense current near X-type neutral points (where the magnetic field vanishes). These sheets are important as sites where the magnetic-field energy is converted efficiently into heat and bulk kinetic energy and where particles can be accelerated to high energies. Examples include disruptions in laboratory tokamaks, substorms in the earth's magnetosphere, and flares on the sun. The basic behavior of a one-dimensional sheet is presented, together with an account of the linear tearing-mode instability that can cause the field lines in such a sheet to reconnect. Such reconnection may develop in different ways: it may arise from a spontaneous instability or it may be driven, either from outside by motions or locally by a resistivity enhancement. Various processes are described that may occur during the nonlinear development of tearing, along with the many numerical and laboratory experiments that are aiding our understanding of this intriguing cosmical process.
Scott, Michael D.; Buller, David B.; Walkosz, Barbara J.; Andersen, Peter A.; Cutter, Gary R.; Dignan, Mark B.
2009-01-01
This is the story of Go Sun Smart, a worksite wellness program endorsed by the North American Ski Area Association and funded by the National Cancer Institute. Between 2000 and 2002 we designed and implemented a large-scale worksite intervention at over 300 ski resorts in North America with the objective of reducing ski area employees and guests risk for skin cancer by adopting sun safe practices. The following narrative describes the intervention in toto from its design and implementation through assessment. Our theory driven, experimentally tested intervention was successful in reducing employees’ risks for skin cancer during and after the ski season. We also succeeded in making ski area guests more aware of the need to take sun safe precautions with both themselves and their children. PMID:20148119
NASA Astrophysics Data System (ADS)
Emel'yanenko, V. V.
2017-01-01
As follows from dynamical studies, in the course of evolution, most near-Earth objects reach orbits with small perihelion distances. Changes of the asteroids in the vicinity of the Sun should play a key role in forming the physical properties, size distribution, and dynamical features of the near-Earth objects. Only seven of the discovered asteroids are currently moving along orbits with perihelion distances q < 0.1 AU. However, due to the Kozai-Lidov secular perturbations, the asteroids, having recently passed near the Sun, could by now have moved to orbits farther from the Sun. In this study, we found asteroids that have been recently orbiting with perihelion distances q < 0.1 AU. Asteroids may be on such orbits for hundreds to tens of thousands of years. To carry out astrophysical observations of such objects is a high priority.
Sun direction detection system
NASA Technical Reports Server (NTRS)
Schmidt, L. F.; Pace, G. D., Jr. (Inventor)
1977-01-01
One of the detectors is an illumination detector consisting of two spaced apart elongated strips with a strip of cadmium sulphide (Cds) deposited therebetween. Whenever the line image impinges the CdS strip, the resistance between the two other strips is relatively low, while being high when the line image is outside the field of view of the illumination detector. Also included is a sun angle detector which consists of a vapor deposited resistor strip connected at one end to plus 10v and at the other end to minus 10v. Spaced apart from the resistor strip is an elongated strip of low resistance material acting as an output strip, with a CdS strip between the two strips. When the line image is within the field of view of the sun angle detector, the output voltage at the output strip depends on the position of the line image across the sun angle detector.
Structure Formation through Magnetohydrodynamical Instabilities in Protoplanetary Disks
NASA Astrophysics Data System (ADS)
Noguchi, K.; Tajima, T.; Horton, W.
2000-12-01
The shear flow instabilities under the presence of magnetic fields in the protoplanetary disk can greatly facilitate the formation of density structures that serve as seeds prior to the onset of the gravitational Jeans instability. Such a seeding process may explain several outstanding puzzles in the planetary genesis that are further compounded by the new discoveries of extrasolar planets and a new insight into the equation of state of dense matter. This puzzle also includes the apparent narrow window of the age difference of the Sun and the Earth. We evaluate the effects of the Parker, magnetorotational(Balbus-Hawley), and kinematic dynamo instabilities by comparing the properties of these instabilities. We calculate the mass spectra of aggregated density structures by the above mechanism in the radial direction for an axisymmetric magnetohydrodynamic(MHD) torus equiblium and power-law density profile models. The mass spectrum of the magnetorotational instability may describe the origin of giant planets away from the central star such as Jupiter. Our local three-dimentional MHD simulation indicates that the coupling of the Parker and magnetorotational instabilities creates spiral arms and gas blobs in the accretion disk, reinforcing the theory and model.
Raphaldini, Breno; Raupp, Carlos F. M. E-mail: carlos.raupp@iag.usp.br
2015-01-20
The solar dynamo is known to be associated with several periodicities, with the nearly 11/22 yr cycle being the most pronounced one. Even though these quasiperiodic variations of solar activity have been attributed to the underlying dynamo action in the Sun's interior, a fundamental theoretical description of these cycles is still elusive. Here, we present a new possible direction in understanding the Sun's cycles based on resonant nonlinear interactions among magnetohydrodynamic (MHD) Rossby waves. The WKB theory for dispersive waves is applied to magnetohydrodynamic shallow-water equations describing the dynamics of the solar tachocline, and the reduced dynamics of a resonant triad composed of MHD Rossby waves embedded in constant toroidal magnetic field is analyzed. In the conservative case, the wave amplitudes evolve periodically in time, with periods on the order of the dominant solar activity timescale (∼11 yr). In addition, the presence of linear forcings representative of either convection or instabilities of meridionally varying background states appears to be crucial in balancing dissipation and thus sustaining the periodic oscillations of wave amplitudes associated with resonant triad interactions. Examination of the linear theory of MHD Rossby waves embedded in a latitudinally varying mean flow demonstrates that MHD Rossby waves propagate toward the equator in a waveguide from –35° to 35° in latitude, showing a remarkable resemblance to the structure of the butterfly diagram of the solar activity. Therefore, we argue that resonant nonlinear magnetohydrodynamic Rossby wave interactions might significantly contribute to the observed cycles of magnetic solar activity.
NASA Technical Reports Server (NTRS)
Ulrich, Roger K.
1993-01-01
The sun serves as an important test case for a variety of problems related to stellar structure and evolution as well as fundamental physics. The sun also influences the terrestrial environment through its varied outputs. These two aspects of the solar interior combine to generate a surprising level of controversy for such an inherently simple star. I review three topics each of which is the subject of some degree of controversy: 1) the solar neutrino problem, 2) the status of modeling and observational efforts to understand the solar cycle of activity, and 3) observational efforts to detect and identify solar g-modes.
NASA Technical Reports Server (NTRS)
2004-01-01
This animation shows the transit of Mars' moon Phobos across the Sun. It is made up of images taken by the Mars Exploration Rover Opportunity on the morning of the 45th martian day, or sol, of its mission. This observation will help refine our knowledge of the orbit and position of Phobos. Other spacecraft may be able to take better images of Phobos using this new information. This event is similar to solar eclipses seen on Earth in which our Moon passes in front of the Sun. The images were taken by the rover's panoramic camera.
Irradiance Variability of the Sun
NASA Technical Reports Server (NTRS)
Froehlich, Claus
1990-01-01
Direct measurements of the solar constant--the total irradiance at mean Sun-Earth distance--during the last ten years from satellites show variations over time scales from minutes to years and decades. At high frequencies the spectral power is determined by granulation, super- and mesogranulation. In the 5-minute range, moreover, it is dominated by power from the solar p-mode oscillations. Their power and frequencies change with time, yielding information about changes in the convection zone. During periods of several hours, the power is steadily increasing and may be partly due to solar gravity modes. The most important variance is in the range from days to several months and is related to the photospheric features of solar activity, decrease of the irradiance during the appearance of sunspots, and increasing by faculae and the magnetic network. Long-term modulation by the 11-year activity cycle are observed conclusively with the irradiance being higher during solar maximum. All these variations can be explained--at least qualitatively--by their manifestation on the photosphere. For the long-term changes, the simultaneous changes of the frequencies of solar p-mode oscillations suggest a more global origin of the variations. Indeed, it seems that the observed irradiance modulation is a true luminosity change with the magnetic cycle of the Sun.
ERIC Educational Resources Information Center
Demski, Jennifer
2013-01-01
The University of San Diego (USD) and Point Loma Nazarene University (PLNU) are licensing the sun. Both California schools are generating solar power on campus without having to sink large amounts of capital into equipment and installation. By negotiating power purchasing agreements (PPAs) with Amsolar and Perpetual Energy Systems, respectively,…
On August 3, the sun packed a double punch, emitting a M6.0-class flare at 9:43 am EDT. This video is of the second, slightly stronger M9.3-class flare at 11:41 pm EDT. Both flares had significant ...
ERIC Educational Resources Information Center
Brown, D. S.
2009-01-01
The Sun's atmosphere is a highly structured but dynamic place, dominated by the solar magnetic field. Hot charged gas (plasma) is trapped on lines of magnetic force that can snap like an elastic band, propelling giant clouds of material out into space. A range of ground-based and space-based solar telescopes observe these eruptions, particularly…
ERIC Educational Resources Information Center
Scott, Michael D.; Buller, David B.; Walkosz, Barbara J.; Andersen, Peter A.; Cutter, Gary R.; Dignan, Mark B.
2008-01-01
This is the story of Go Sun Smart, a worksite wellness program endorsed by the North American Ski Area Association and funded by the National Cancer Institute. Between 2000 and 2002 we designed and implemented a large-scale worksite intervention at over 300 ski resorts in North America with the objective of reducing ski area employees and guests…
Atmospheric Science Data Center
2014-05-15
... of the Sun, the solar power stations in California's Mohave Desert can reflect solar energy from their large, mirror-like surfaces directly ... array at Harper Lake (upper right-hand corner). The Mohave Desert SEGS are the largest collection of solar fields in the world. Together ...
NASA Technical Reports Server (NTRS)
Adams, Mitzi L.; Bero, Elizabeth; Sever, Thomas L.
1999-01-01
Leveraging funds from NASA's Initiative to Develop Education through Astronomy and Space Science (IDEAS) program, we combined the expertise of an archaeoastronomer, a solar scientist, and a teacher to trace humankind's view of the Sun and how that has changed, from the time of Stonehenge in about 1800 B.C.E., to the time of the Maya in 700 C.E., up to the modem era. Our program was aimed at middle-school students in an attempt to explain not only how science is done today, but how science has evolved from the observations of ancient societies. From these varied cultures, we touched on methods of observing the Sun, ideas of the composition of the Sun, and the relationship of the Sun to everyday life. Further, using the von Braun Astronomical Society's Planetarium in Huntsville, Alabama as a test-bed for the program, we illustrated concepts such as solstices, equinoxes, and local noon with approximately 800 eighth grade students from the local area. Our presentation to SEPA will include a description of NASA's IDEAS program and how to go about partnering with a NASA astronomer, some slides from our planetarium program and web-site, and some hands-on activities.
NASA Technical Reports Server (NTRS)
2007-01-01
Michael Sandras, a member of the Pontchartrain Astronomical Society, explains his solar telescope to students of Second Street in Bay St. Louis, Hancock County and Nicholson elementary schools in StenniSphere's Millennium Hall on April 10. The students participated in several hands-on activities at Stennis Space Center's Sun-Earth Day celebration.
NASA Astrophysics Data System (ADS)
Robitaille, Pierre-Marie
2014-03-01
For 150 years, the Sun has been seen as a gaseous object devoid of a surface, as required by the Standard Solar Model (SSM). Yet, not one line of observational evidence supports a gaseous Sun. In contrast, overwhelming evidence exists that the Sun is comprised of condensed matter. Recently, 40 proofs have been compiled in conjunction with the Liquid Metallic Hydrogen Solar Model (LMHSM). This model advances that the Sun has a true surface. Photospheric structures, such as sunspots, granules, and faculae, are not optical illusions, as in the SSM, but real objects with a condensed nature. The LMHSM accounts for the thermal spectrum by invoking true inter-atomic structure on the photosphere in the form of the graphite-like layered hexagonal metallic hydrogen lattice first proposed by Wigner and Huntington. Within the convection zone, layered metallic hydrogen, insulated by intercalate atoms, enables the generation of the solar dynamo. Electrons located in conduction bands provide a proper means of generating magnetic fields. Metallic hydrogen ejected from the photosphere also thinly populates the corona, as reflected by the continuous K-coronal spectrum. This coronal matter harvests electrons, resulting in the production of highly ionized atoms. Electron affinity, not temperature, governs the ion profile. The chromosphere is a site of hydrogen and proton capture. Line emission in this region, strongly supports the idea that exothermic condensation reactions are occurring in the chromosphere. In the LMHSM, solar activity and solar winds are regulated by exfoliation reactions occurring in the Sun itself, as the metallic hydrogen lattice excludes non-hydrogen elements from the solar body.
Multi-region relaxed magnetohydrodynamics with flow
Dennis, G. R. Dewar, R. L.; Hole, M. J.; Hudson, S. R.
2014-04-15
We present an extension of the multi-region relaxed magnetohydrodynamics (MRxMHD) equilibrium model that includes plasma flow. This new model is a generalization of Woltjer's model of relaxed magnetohydrodynamics equilibria with flow. We prove that as the number of plasma regions becomes infinite, our extension of MRxMHD reduces to ideal MHD with flow. We also prove that some solutions to MRxMHD with flow are not time-independent in the laboratory frame, and instead have 3D structure which rotates in the toroidal direction with fixed angular velocity. This capability gives MRxMHD potential application to describing rotating 3D MHD structures such as 'snakes' and long-lived modes.
Hall-magnetohydrodynamic turbulence with electron inertia
NASA Astrophysics Data System (ADS)
Martin, L. N.; Andres, N.; Dmitruk, P.; Gomez, D. O.
2013-12-01
The magnetohydrodynamic (one-fluid) model is often regarded as a reasonable description of the dynamics of a plasma. One-fluid models are useful in the context of large scale dynamics, but when a more detailed description is needed (for instance, when the physical context favors the development of small scales) it is most appropriate to consider two-fluid models. Within the framework of two-fluid MHD for a fully ionized hydrogen plasma, we study the effect of the Hall term and electron inertia in MHD turbulence, observing whether these effects change the energy cascade, the characteristic scales of the flow and the dynamics of global magnitudes, with particular interest in the dissipation processes. Numerical simulations of freely evolving three-dimensional reduced magnetohydrodynamics (RHMHD) and 2.5-D Hall-MHD including electron inertia are performed for different values of the ion and electron skin depth (controlling the impact of the Hall term and the electron inertia).
Magnetohydrodynamic equilibria with incompressible flows: Symmetry approach
Cicogna, G.; Pegoraro, F.
2015-02-15
We identify and discuss a family of azimuthally symmetric, incompressible, magnetohydrodynamic plasma equilibria with poloidal and toroidal flows in terms of solutions of the Generalized Grad Shafranov (GGS) equation. These solutions are derived by exploiting the incompressibility assumption, in order to rewrite the GGS equation in terms of a different dependent variable, and the continuous Lie symmetry properties of the resulting equation and, in particular, a special type of “weak” symmetries.
Lattice Boltzmann model for simulation of magnetohydrodynamics
NASA Technical Reports Server (NTRS)
Chen, Shiyi; Chen, Hudong; Martinez, Daniel; Matthaeus, William
1991-01-01
A numerical method, based on a discrete Boltzmann equation, is presented for solving the equations of magnetohydrodynamics (MHD). The algorithm provides advantages similar to the cellular automaton method in that it is local and easily adapted to parallel computing environments. Because of much lower noise levels and less stringent requirements on lattice size, the method appears to be more competitive with traditional solution methods. Examples show that the model accurately reproduces both linear and nonlinear MHD phenomena.
New cellular automaton model for magnetohydrodynamics
NASA Technical Reports Server (NTRS)
Chen, Hudong; Matthaeus, William H.
1987-01-01
A new type of two-dimensional cellular automation method is introduced for computation of magnetohydrodynamic fluid systems. Particle population is described by a 36-component tensor referred to a hexagonal lattice. By appropriate choice of the coefficients that control the modified streaming algorithm and the definition of the macroscopic fields, it is possible to compute both Lorentz-force and magnetic-induction effects. The method is local in the microscopic space and therefore suited to massively parallel computations.
Nuclear Electric Magnetohydrodynamic Propulsion for Submarine
1989-05-01
Magnetohydrodynamic Theory 24 2.3 MHD Pump Analysis 29 2.4 Maximum Pump Efficiency and Power 33 2.5 MHD Electrical Generator 40 2.6 MHD Generator Requirements 44 3...propulsion was first demon- strated by Stewart Way who published a very complete and mathematically rigorous analysis of an external duct, DC...in simple analysis and still apply in a complicated cases which require computer or physical modeling. As mentioned before, the MHD generator works on
Geomagnetic main field modeling using magnetohydrodynamic constraints
NASA Technical Reports Server (NTRS)
Estes, R. H.
1985-01-01
The influence of physical constraints are investigated which may be approximately satisfied by the Earth's liquid core on models of the geomagnetic main field and its secular variation. A previous report describes the methodology used to incorporate nonlinear equations of constraint into the main field model. The application of that methodology to the GSFC 12/83 field model to test the frozen-flux hypothesis and the usefulness of incorporating magnetohydrodynamic constraints for obtaining improved geomagnetic field models is described.
Guiding Center Equations for Ideal Magnetohydrodynamic Modes
Roscoe B. White
2013-02-21
Guiding center simulations are routinely used for the discovery of mode-particle resonances in tokamaks, for both resistive and ideal instabilities and to find modifications of particle distributions caused by a given spectrum of modes, including large scale avalanches during events with a number of large amplitude modes. One of the most fundamental properties of ideal magnetohydrodynamics is the condition that plasma motion cannot change magnetic topology. The conventional representation of ideal magnetohydrodynamic modes by perturbing a toroidal equilibrium field through δ~B = ∇ X (ξ X B) however perturbs the magnetic topology, introducing extraneous magnetic islands in the field. A proper treatment of an ideal perturbation involves a full Lagrangian displacement of the field due to the perturbation and conserves magnetic topology as it should. In order to examine the effect of ideal magnetohydrodynamic modes on particle trajectories the guiding center equations should include a correct Lagrangian treatment. Guiding center equations for an ideal displacement ξ are derived which perserve the magnetic topology and are used to examine mode particle resonances in toroidal confinement devices. These simulations are compared to others which are identical in all respects except that they use the linear representation for the field. Unlike the case for the magnetic field, the use of the linear field perturbation in the guiding center equations does not result in extraneous mode particle resonances.
Guiding center equations for ideal magnetohydrodynamic modes
White, R. B.
2013-04-15
Guiding center simulations are routinely used for the discovery of mode-particle resonances in tokamaks, for both resistive and ideal instabilities and to find modifications of particle distributions caused by a given spectrum of modes, including large scale avalanches during events with a number of large amplitude modes. One of the most fundamental properties of ideal magnetohydrodynamics is the condition that plasma motion cannot change magnetic topology. The conventional representation of ideal magnetohydrodynamic modes by perturbing a toroidal equilibrium field through {delta}B-vector={nabla} Multiplication-Sign ({xi}-vector Multiplication-Sign B-vector), however, perturbs the magnetic topology, introducing extraneous magnetic islands in the field. A proper treatment of an ideal perturbation involves a full Lagrangian displacement of the field due to the perturbation and conserves magnetic topology as it should. In order to examine the effect of ideal magnetohydrodynamic modes on particle trajectories, the guiding center equations should include a correct Lagrangian treatment. Guiding center equations for an ideal displacement {xi}-vector are derived which preserve the magnetic topology and are used to examine mode particle resonances in toroidal confinement devices. These simulations are compared to others which are identical in all respects except that they use the linear representation for the field. Unlike the case for the magnetic field, the use of the linear field perturbation in the guiding center equations does not result in extraneous mode particle resonances.
Pagoto, Sherry; McChargue, Dennis; Fuqua, R Wayne
2003-07-01
Skin cancer is the most prevalent of all cancers in the United States. Although avoiding sun exposure and using sun protection reduces skin cancer risk, rates of such behaviors are moderate at best. The present study examined the impact of a multicomponent intervention that aimed to increase the saliency of skin cancer risk while promoting the use of sun protection. Midwestern beachgoers (n = 100) participated in an intervention or questionnaire-only control group. Sun protection, stage of change, and sun exposure were measured at baseline and 2-month follow-up. The intervention group significantly improved in sun protection use and stage of change, but not sun exposure, compared with the control group. Personalizing the risks of unprotected sun exposure combined with providing education about sun protection facilitated healthy changes in behavior and motivation.
NASA Astrophysics Data System (ADS)
Pecker, Jean-Claude
After a definition of the various terms used to identify the solar layers, from the center to the exterior, and a physical description of these layers, it is shown that various couplings are controlling the physics in the core and the outer layers, and even the planets. One of these couplings is between convection, rotation and magnetism (the dynamo), and another coupling is between solar activity and planetary physics. These couplings make it possible to use observed data (oscillations, neutrinos, emergence of active regions, and of course their evolution) to infer properties of the solar interior. The theoretical knowledge of the sun must take into account the existence of these couplings, as well as the existence of another type of coupling, the one that links the past and the present states of the sun.
NASA Technical Reports Server (NTRS)
Christensen-Dalsgaard, J.; Gough, D.; Toomre, J.
1985-01-01
The use of the sun's oscillations, caused by the constructive interference between internally reflected waves, to study the interior of the sun is examined. Pressure and buoyancy have the strongest influence on oscillations; pressure fluctuations at high frequency produce acoustic waves and at low frequency buoyancy produces internal gravity waves. The theory of acoustic wave frequency, which is used to determine measurements of sound speed and rate of rotation of the solar interior as well as the thickness of the convection zone, is presented. The classification of solar oscillations is described. The models for acoustic modes of low degree and intermediate degree are discussed. The effect of internal speed, gravity modes, and solar rotation on solar models is determined. The oscillation frequencies yield an He abundance that is consistent with cosmology, but they reinforce the severity of the neutrino problem.
Cannavò, Serafinella Patrizia; Borgia, Francesco; Trifirò, Caterina; Aragona, Emanuela
2013-01-01
Fisherman commonly experience a significant number of cutaneous problems, related to the exposure to environmental factors due to their working conditions. Among these factors, sun exposure is able to determine both acute and chronic skin damage, mostly linked to the effects of the ultraviolet (UV) radiation on epidermal and dermal structures. In particular, UV-A appears to play a major role in the deterioration of dermal structure leading to the photoaged appearance of the skin, while UV-B is mainly responsible for skin cancers. Peculiar clinical features of skin damage in fishermen include dryness, irregular pigmentation, wrinkling, stellate pseudoscars, elastosis, inelasticity, telangiectasia, comedones and sebaceous hyperplasia. Furtheremore, the high incidence of non-melanoma skin cancers, on sun-exposed areas, confirms the need for occupational health policies focusing on issues such as photoprotection.
NASA Technical Reports Server (NTRS)
1973-01-01
Articles pertaining to the solar studies and the Skylab program are presented, with emphasis on the usefulness of the Apollo Telescope Mount (ATM) program. A description of Skylab objectives and key mission events is included along with articles about the sun. Skylab solar studies which are reported include these topics: ATM solar observatory, scientific instruments, crew operations and crew training, and the joint observing program. The Skylab associated solar programs are also reported.
Guilford, Tim; Taylor, Graham K.
2014-01-01
Many animals, and birds in particular, are thought to use directional information from the sun in the form of a time-compensated sun compass, with predictably deviated orientation under clock shift being regarded as the litmus test of this. We suggest that this paradigm obscures a number of other ways in which solar-derived information could be important in animal orientation. We distinguish between the known use of the sun's azimuth to provide absolute geographical direction (compass mechanism) and its possible use to detect changes in heading (heading indicator mechanism). Just as in an aircraft, these two kinds of information may be provided by separate mechanisms and used for different functions, for example for navigation versus steering. We also argue that although a solar compass must be time-referenced to account for the sun's apparent diurnal movement, this need not entail full time compensation. This is because animals might also use time-dependent solar information in an associatively acquired, and hence time-limited, way. Furthermore, we show that a solar heading indicator, when used on a sufficiently short timescale, need not require time compensation at all. Finally, we suggest that solar-derived cues, such as shadows, could also be involved in navigation in ways that depend explicitly upon position, and are therefore not strictly compass-related. This could include giving directionality to landmarks, or acting as time-dependent landmarks involved in place recognition. We conclude that clock shift experiments alone are neither necessary nor sufficient to identify the occurrence of all conceivable uses of solar information in animal orientation, so that a predictable response to clock shift should not be regarded as an acid test of the use of solar information in navigation. PMID:25389374
Guilford, Tim; Taylor, Graham K
2014-11-01
Many animals, and birds in particular, are thought to use directional information from the sun in the form of a time-compensated sun compass, with predictably deviated orientation under clock shift being regarded as the litmus test of this. We suggest that this paradigm obscures a number of other ways in which solar-derived information could be important in animal orientation. We distinguish between the known use of the sun's azimuth to provide absolute geographical direction (compass mechanism) and its possible use to detect changes in heading (heading indicator mechanism). Just as in an aircraft, these two kinds of information may be provided by separate mechanisms and used for different functions, for example for navigation versus steering. We also argue that although a solar compass must be time-referenced to account for the sun's apparent diurnal movement, this need not entail full time compensation. This is because animals might also use time-dependent solar information in an associatively acquired, and hence time-limited, way. Furthermore, we show that a solar heading indicator, when used on a sufficiently short timescale, need not require time compensation at all. Finally, we suggest that solar-derived cues, such as shadows, could also be involved in navigation in ways that depend explicitly upon position, and are therefore not strictly compass-related. This could include giving directionality to landmarks, or acting as time-dependent landmarks involved in place recognition. We conclude that clock shift experiments alone are neither necessary nor sufficient to identify the occurrence of all conceivable uses of solar information in animal orientation, so that a predictable response to clock shift should not be regarded as an acid test of the use of solar information in navigation.
NASA Astrophysics Data System (ADS)
Noyes, R. W.
Observational data, analytical models, and instrumentation used to study the sun and its evolution are detailed, and attention is given to techniques for converting solar energy to useful power on earth. The star ignited when the mutual gravitational attractions of dust and vapor in a primordial cloud in the Galaxy caused an in-rush of accelerating particles which eventually became dense enough to ignite. The heat grew until inward rushing matter was balanced by outward moving radiative forces. The planets formed from similar debris, and solar radiation is suggested to have triggered the chemical reactions giving rise to life on earth. Visual, spectroscopic, coronagraphic, and UV observations of the sun from the ground and from spacecraft, particularly Skylab, are described, together with features of the solar surface, magnetic field, sunspots, and coronal loops. Models for the processes that occur in the solar interior are explored, as are the causes of solar flares. Attention is given to solar cells, heliostat arrays, wind turbines, and water turbines as means to convert, either directly or indirectly, the earth-bound solar energy to electrical and thermal power. Finally, the life cycle of the sun, about 9 billion yr in duration, is summarized, noting the current status of midlife.
Saturation of Stellar Winds from Young Suns
NASA Astrophysics Data System (ADS)
Suzuki, Takeru K.; Imada, Shinsuke; Kataoka, Ryuho; Kato, Yoshiaki; Matsumoto, Takuma; Miyahara, Hiroko; Tsuneta, Saku
2013-10-01
We investigated mass losses via stellar winds from Sun-like main-sequence stars with a wide range of activity levels. We performed forward-type magnetohydrodynamical numerical experiments for Alfvén wave-driven stellar winds with a wide range of input Poynting flux from the photosphere. Increasing the magnetic field strength and the turbulent velocity at the stellar photosphere from the current solar level, the mass-loss rate rapidly at first increases, owing to suppression of the reflection of the Alfvén waves. The surface materials are lifted up by the magnetic pressure associated with the Alfvén waves, and the cool dense chromosphere is intermittently extended to 10%#8211;20% of the stellar radius. The dense atmospheres enhance the radiative losses, and eventually most of the input Poynting energy from the stellar surface escapes by radiation. As a result, there is no more sufficient energy remaining for the kinetic energy of the wind; the stellar wind saturates in very active stars, as observed in Wood et al. (2002, ApJ, 574, 412; 2005, ApJ, 628, L143). The saturation level is positively correlated with Br,0 f0, where Br,0 and f0 are the magnetic field strength and the filling factor of open flux tubes at the photosphere. If Br,0 f0 is relatively large gtrsim 5 G, the mass-loss rate could be as high as 1000 times. If such a strong mass loss lasts for ˜ 1 billion years, the stellar mass itself would be affected, which could be a solution to the faint young Sun paradox. We derived a Reimers-type scaling relation that estimates the mass-loss rate from an energetics consideration of our simulations. Finally, we derived the evolution of the mass-loss rates, dot;{M} ∝ t-1.23, of our simulations, combining with an observed time evolution of X-ray flux from Sun-like stars, which are shallower than dot;{M} ∝ t-2.33±0.55 in Wood et al. (2005).
Carousel Trackers with 1-Sun or 3-Sun Modules for Commercial Building Rooftops
Gehl, Anthony C; Maxey, L Curt; Fraas, Dr. Lewis; Avery, James E.; Minkin, Leonid M; Huang, H,
2008-01-01
The goal is lower cost solar electricity. Herein, two evolutional steps are described toward achieving this goal. The first step is to follow the sun with a solar tracker. Herein, a carousel tracker is described for mounting on commercial building flat rooftops in order to produce more kWh per kW relative to fixed PV modules. The second evolutionary improvement is to produce lower cost 3-sun CPV modules where two thirds of the expensive single crystal silicon material is replaced by less expensive mirror material. This paper describes the performance and durability of two prototype installations demonstrating these evolutionary innovations. In the first case, the installation and operation of 2 carousels equipped with traditional flat plate modules is described. In the second case, the operation of a carousel equipped with new 3-sun CPV modules is described. Both systems have been operating as expected for several months through the winter of 2007.
NASA Astrophysics Data System (ADS)
Davidson, Wayne P. S.; van der Werf, Siebren Y.
2005-09-01
Special variants of the Novaya Zemlya effect may arise from localized temperature inversions that follow the height profile of hills or mountains. Rather than following its natural path, the rising or setting Sun may, under such circumstances, appear to slide along a distant mountain slope. We found early observations of this effect in the literature by Willem Barents (1597) and by Captain Scott and H. G. Ponting (1911). We show recent photographic material of the effect and present ray-tracing calculations to explain its essentials.
NASA Technical Reports Server (NTRS)
Frank, A.; Derespinis, S. F.; Mockovciak, John, Jr.
1986-01-01
Window-shade type spring roller contains blanket, taken up by rotating cylindrical frame and held by frame over area to be shaded. Blanket made of tough, opaque polyimide material. Readily unfurled by mechanism to protect space it encloses from Sun. Blanket forms arched canopy over space and allows full access to it from below. When shading not needed, retracted mechanism stores blanket compactly. Developed for protecting sensitive Space Shuttle payloads from direct sunlight while cargo-bay doors open. Adapted to shading of greenhouses, swimming pools, and boats.
Christensen-Dalsgaard, J; Gough, D; Toomre, J
1985-09-06
Oscillations of the sun make it possible to probe the inside of a star. The frequencies of the oscillations have already provided measures of the sound speed and the rate of rotation throughout much of the solar interior. These quantities are important for understanding the dynamics of the magnetic cycle and have a bearing on testing general relativity by planetary precession. The oscillation frequencies yield a helium abundance that is consistent with cosmology, but they reinforce the severity of the neutrino problem. They should soon provide an important standard by which to calibrate the theory of stellar evolution.
NASA Astrophysics Data System (ADS)
Broggini, Carlo; LUNA Collaboration
2014-05-01
One of the main ingredients of nuclear astrophysics is the knowledge of the thermonu-clear reactions responsible for the stellar luminosity and for the synthesis of the chemical elements. Deep underground in the Gran Sasso Laboratory the cross section of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The main results obtained in the past 20 years are reviewed and their influence on our understanding of the properties of the neutrino and the Sun is discussed.
Broggini, Carlo; Collaboration: LUNA Collaboration
2014-05-09
One of the main ingredients of nuclear astrophysics is the knowledge of the thermonu-clear reactions responsible for the stellar luminosity and for the synthesis of the chemical elements. Deep underground in the Gran Sasso Laboratory the cross section of the key reactions of the proton-proton chain and of the Carbon-Nitrogen-Oxygen (CNO) cycle have been measured right down to the energies of astrophysical interest. The main results obtained in the past 20 years are reviewed and their influence on our understanding of the properties of the neutrino and the Sun is discussed.
Broken symmetry in ideal magnetohydrodynamic turbulence
NASA Technical Reports Server (NTRS)
Shebalin, John V.
1993-01-01
A numerical study of the long-time evolution of a number of cases of inviscid, isotropic, incompressible, three-dimensional fluid, and magneto-fluid turbulence has been completed. The results confirm that ideal magnetohydrodynamic turbulence is non-ergodic if there is no external magnetic field present. This is due essentially to a canonical symmetry being broken in an arbitrary dynamical representation. The broken symmetry manifests itself as a coherent structure, i.e., a non-zero time-averaged part of the turbulent magnetic field. The coherent structure is observed, in one case, to contain about eighteen percent of the total energy.
Classes of Hydrodynamic and Magnetohydrodynamic Turbulent Decay
NASA Astrophysics Data System (ADS)
Brandenburg, Axel; Kahniashvili, Tina
2017-02-01
We perform numerical simulations of decaying hydrodynamic and magnetohydrodynamic turbulence. We classify our time-dependent solutions by their evolutionary tracks in parametric plots between instantaneous scaling exponents. We find distinct classes of solutions evolving along specific trajectories toward points on a line of self-similar solutions. These trajectories are determined by the underlying physics governing individual cases, while the infrared slope of the initial conditions plays only a limited role. In the helical case, even for a scale-invariant initial spectrum (inversely proportional to wave number k ), the solution evolves along the same trajectory as for a Batchelor spectrum (proportional to k4).
Nonlinear magnetohydrodynamics by Galerkin-method computation
NASA Technical Reports Server (NTRS)
Shan, Xiaowen; Montgomery, David; Chen, Hudong
1991-01-01
A fully spectral numerical code is used to explore the properties of voltage-driven dissipative magnetofluids inside a periodic cylinder with circular cross section. The trial functions are orthonormal eigenfunctions of the curl (Chandrasekhar-Kendall functions). Transitions are observed from axisymmetric resistive equilibria without flow to helically deformed laminar states with flow, and between pairs of helical laminar states with different pairs of poloidal and toroidal m and n numbers. States of minimum energy dissipation rate seem to be preferred. At high values of the pinch ratio, fully developed magnetohydrodynamic turbulence is observed.
Magnetohydrodynamic effects in liquid metal batteries
NASA Astrophysics Data System (ADS)
Stefani, F.; Galindo, V.; Kasprzyk, C.; Landgraf, S.; Seilmayer, M.; Starace, M.; Weber, N.; Weier, T.
2016-07-01
Liquid metal batteries (LMBs) consist of two liquid metal electrodes and a molten salt ionic conductor sandwiched between them. The density ratios allow for a stable stratification of the three layers. LMBs were already considered as part of energy conversion systems in the 1960s and have recently received renewed interest for economical large-scale energy storage. In this paper, we concentrate on the magnetohydrodynamic aspects of this cell type with special focus on electro-vortex flows and possible effects of the Tayler instability.
Triana Safehold: A New Gyroless, Sun-Pointing Attitude Controller
NASA Technical Reports Server (NTRS)
Chen, J.; Morgenstern, Wendy; Garrick, Joseph
2001-01-01
Triana is a single-string spacecraft to be placed in a halo orbit about the sun-earth Ll Lagrangian point. The Attitude Control Subsystem (ACS) hardware includes four reaction wheels, ten thrusters, six coarse sun sensors, a star tracker, and a three-axis Inertial Measuring Unit (IMU). The ACS Safehold design features a gyroless sun-pointing control scheme using only sun sensors and wheels. With this minimum hardware approach, Safehold increases mission reliability in the event of a gyroscope anomaly. In place of the gyroscope rate measurements, Triana Safehold uses wheel tachometers to help provide a scaled estimation of the spacecraft body rate about the sun vector. Since Triana nominally performs momentum management every three months, its accumulated system momentum can reach a significant fraction of the wheel capacity. It is therefore a requirement for Safehold to maintain a sun-pointing attitude even when the spacecraft system momentum is reasonably large. The tachometer sun-line rate estimation enables the controller to bring the spacecraft close to its desired sun-pointing attitude even with reasonably high system momentum and wheel drags. This paper presents the design rationale behind this gyroless controller, stability analysis, and some time-domain simulation results showing performances with various initial conditions. Finally, suggestions for future improvements are briefly discussed.
ERIC Educational Resources Information Center
Pasachoff, Jay M.
1991-01-01
Both the "quiet" sun and the "active" sun are described. The quiet sun includes the solar phenomena that occur everyday and the active sun includes solar phenomena that appear nonuniformly on the sun and vary over time. A general description of the sun, sunspots, flares, plages, filaments, prominences, solar-terrestrial…
NASA Technical Reports Server (NTRS)
Adams, Mitzi L.; Sever, Thomas L.; Bero, Elizabeth
1998-01-01
Using a grant from NASA's Initiative to Develop Education through Astronomy and Space Science (IDEAS) program, we have developed an inter-disciplinary curriculum for middle-school students which targets both history and astronomy. Our curriculum explores the attitudes and techniques of ancient spiritual leaders, specifically those of the Maya and Inca cultures, who observed and tried to control the Sun. We wish students to understand the probable importance of astronomical observations to these ancient peoples. In addition, using the experience of an archaeologist, we show how modern techniques of viewing the Earth through satellite imagery, has allowed the re-discovery of ancient sites where solar observations and attempted manipulation of the universe took place. To contrast ancient observations of the Sun with modern ones, we use the experience of a solar astronomer and bring to the classroom up-to-date information about solar astronomy and the impact of solar activity on the Earth's environment. In this presentation, we will present fragments of our curriculum as well as results from pre- and post-tests given to participating groups of students. Finally, we will discuss comments from local middle-school teachers who were asked to evaluate our curriculum.
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2015-11-01
The Sun often exhibits outbursts, launching material from its surface in powerful releases of energy. Recent analysis of such an outburst captured on video by several Sun-monitoring spacecraft may help us understand the mechanisms that launch these eruptions.Many OutburstsSolar jets are elongated, transient structures that are thought to regularly release magnetic energy from the Sun, contributing to coronal heating and solar wind acceleration. Coronal mass ejections (CMEs), on the other hand, are enormous blob-like explosions, violently ejecting energy and mass from the Sun at incredible speeds.But could these two types of events actually be related? According to a team of scientists at the University of Science and Technology of China, they may well be. The team, led by Jiajia Liu, has analyzed observations of a coronal jet that they believe prompted the launch of a powerful CME.Observing an ExplosionGif of a movie of the CME, taken by the Solar Dynamics Observatorys Atmospheric Imaging Assembly at a wavelength of 304. The original movie can be found in the article. [Liu et al.]An army of spacecraft was on hand to witness the event on 15 Jan 2013 including the Solar Dynamics Observatory (SDO), the Solar and Heliospheric Observatory (SOHO), and the Solar Terrestrial Relations Observatory (STEREO). The instruments on board these observatories captured the drama on the northern limb of the Sun as, at 19:32 UT, a coronal jet formed. Just eight minutes later, a powerful CME was released from the same active region.The fact that the jet and CME occurred in the same place at roughly the same time suggests theyre related. But did the initial motions of the CME blob trigger the jet? Or did the jet trigger the CME?Tying It All TogetherIn a recently published study, Liu and collaborators analyzed the multi-wavelength observations of this event to find the heights and positions of the jet and CME. From this analysis, they determined that the coronal jet triggered the release
Double-duct liquid metal magnetohydrodynamic engine
Haaland, Carsten M.
1997-01-01
An internal combustion, liquid metal (LM) magnetohydrodynamic (MHD) engine and an alternating current (AC) magnetohydrodynamic generator, are used in combination to provide useful AC electric energy output. The engine design has four pistons and a double duct configuration, with each duct containing sodium potassium liquid metal confined between free pistons located at either end of the duct. The liquid metal is forced to flow back and forth in the duct by the movement of the pistons, which are alternatively driven by an internal combustion process. In the MHD generator, the two LM-MHD ducts pass in close proximity through a Hartmann duct with output transformer. AC power is produced by operating the engine with the liquid metal in the two generator ducts always flowing in counter directions. The amount of liquid metal maintained in the ducts may be varied. This provides a variable stroke length for the pistons. The engine/generator provides variable AC power at variable frequencies that correspond to the power demands of the vehicular propulsion. Also the engine should maintain nearly constant efficiency throughout the range of power usage. Automobiles and trucks could be powered by the invention, with no transmission or power converter devices being required.
Double-duct liquid metal magnetohydrodynamic engine
Haaland, Carsten M.
1995-01-01
An internal combustion, liquid metal (LM) magnetohydrodynamic (MHD) engine and an alternating current (AC) magnetohydrodynamic generator, are used in combination to provide useful AC electric energy output. The engine design has-four pistons and a double duct configuration, with each duct containing sodium potassium liquid metal confined between free pistons located at either end of the duct. The liquid metal is forced to flow back and forth in the duct by the movement of the pistons, which are alternatively driven by an internal combustion process. In the MHD generator, the two LM-MHD ducts pass in close proximity through a Hartmann duct with output transformer. AC power is produced by operating the engine with the liquid metal in the two generator ducts always flowing in counter directions. The amount of liquid metal maintained in the ducts may be varied. This provides a variable stroke length for the pistons. The engine/generator provides variable AC power at variable frequencies that correspond to the power demands of the vehicular propulsion. Also the engine should maintain nearly constant efficiency throughout the range of power usage. Automobiles and trucks could be powered by the invention, with no transmission or power converter devices being required.
Analytical study of magnetohydrodynamic propulsion stability
NASA Astrophysics Data System (ADS)
Abdollahzadeh Jamalabadi, M. Y.
2014-09-01
In this paper an analytical solution for the stability of the fully developed flow drive in a magneto-hydro-dynamic pump with pulsating transverse Eletro-magnetic fields is presented. To do this, a theoretical model of the flow is developed and the analytical results are obtained for both the cylindrical and Cartesian configurations that are proper to use in the propulsion of marine vessels. The governing parabolic momentum PDEs are transformed into an ordinary differential equation using approximate velocity distribution. The numerical results are obtained and asymptotic analyses are built to discover the mathematical behavior of the solutions. The maximum velocity in a magneto-hydro-dynamic pump versus time for various values of the Stuart number, electro-magnetic interaction number, Reynolds number, aspect ratio, as well as the magnetic and electrical angular frequency and the shift of the phase angle is presented. Results show that for a high Stuart number there is a frequency limit for stability of the fluid flow in a certain direction of the flow. This stability frequency is dependent on the geometric parameters of a channel.
Efficient acceleration of relativistic magnetohydrodynamic jets
NASA Astrophysics Data System (ADS)
Toma, Kenji; Takahara, Fumio
2013-08-01
Relativistic jets in active galactic nuclei, galactic microquasars, and gamma-ray bursts are widely considered to be magnetohydrodynamically driven by black hole accretion systems, although the conversion mechanism from the Poynting into the particle kinetic energy flux is still open. Recent detailed numerical and analytical studies of global structures of steady, axisymmetric magnetohydrodynamic (MHD) flows with specific boundary conditions have not reproduced as rapid an energy conversion as required by observations. In order to find more suitable boundary conditions, we focus on the flow along a poloidal magnetic field line just inside the external boundary, without treating the transfield force balance in detail. We find some examples of the poloidal field structure and corresponding external pressure profile for an efficient and rapid energy conversion as required by observations, and that the rapid acceleration requires a rapid decrease of the external pressure above the accretion disk. We also clarify the differences between the fast magnetosonic point of the MHD flow and the sonic point of the de Laval nozzle.
Magnetohydrodynamic stability of stochastically driven accretion flows.
Nath, Sujit Kumar; Mukhopadhyay, Banibrata; Chattopadhyay, Amit K
2013-07-01
We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.
Global Magnetohydrodynamic Modeling of the Solar Corona
NASA Technical Reports Server (NTRS)
Linker, Jon A.
1997-01-01
Under this contract, we have continued our investigations of the large scale structure of the solar corona and inner heliosphere using global magnetohydrodynamic (MHD) simulations. These computations have also formed the basis for studies of coronal mass ejections (CMES) using realistic coronal configurations. We have developed a technique for computing realistic magnetohydrodynamic (MHD) computations of the solar corona and inner heliosphere. To perform computations that can be compared with specific observations, it is necessary to incorporate solar observations into the boundary conditions. We have used the Wilcox Solar Observatory synoptic maps (collected during a solar rotation by daily measurements of the line-of-sight magnetic field at central meridian) to specify the radial magnetic field (B,) at the photosphere. For the initial condition, we use a potential magnetic field consistent with the specified distribution of B, at the lower boundary, and a wind solution consistent with the specified plasma density and temperature at the solar surface. Together this initial condition forms a (non-equilibrium) approximation of the state of the solar corona for the time-dependent MHD computation. The MHD equations are then integrated in time to steady state. Here we describe solutions relevant to a recent solar eclipse, as well as Ulysses observations. We have also developed a model configuration of solar minimum, useful for studying CME initiation and propagation.
Walker, Howard Andrew
2010-12-31
A spreadsheet written in Microsoft Excel that evaluates combinations of renewable energy technologies at a site and identifies the combination that minimizes life cycle cost. Constraints on the optimization such as percent of energy from renewable, available land area; available investment capital, etc make the optimization more useful. Inputs to the model include building location, number of square feet and floors; monthly energy use and cost for electric and any other fuels. Outputs include size of each RE technology total investment, utility costs, O&M costs; percent renewable; life cycle cost; rate of return; CO2 savings.
NASA Astrophysics Data System (ADS)
Soubielle, Marie-Laure
2015-04-01
2015 has been declared the year of light. Sunlight plays a major role in the world. From the sunbeams that heat our planet and feed our plants to the optical analysis of the sun or the modern use of sun particles in technologies, sunlight is everywhere and it is vital. This project aims to understand better the light of the Sun in a variety of fields. The experiments are carried out by students aged 15 to 20 in order to share their discoveries with Italian students from primary and secondary schools. The experiments will also be presented to a group of Danish students visiting our school in January. All experiments are carried out in English and involve teams of teachers. This project is 3 folds: part 1: Biological project = what are the mechanisms of photosynthesis? part 2: Optical project= what are the components of sunlight and how to use it? part 3: Technical project= how to use the energy of sunlight for modern devices? Photosynthesis project Biology and English Context:Photosynthesis is a process used by plants and other organisms to convert light energy, normally from the Sun, into chemical energy that can later fuel the organisms' activities. This chemical energy is stored in molecules which are synthesized from carbon dioxide and water. In most cases, oxygen is released as a waste product. Most plants perform photosynthesis. Photosynthesis maintains atmospheric oxygen levels and supplies all of the organic compounds and most of the energy necessary for life on Earth. Outcome: Our project consists in understanding the various steps of photosynthesis. Students will shoot a DVD of the experiments presenting the equipments required, the steps of the experiments and the results they have obtained for a better understanding of photosynthesis Digital pen project Electricity, Optics and English Context: Sunlight is a complex source of light based on white light that can be decomposed to explain light radiations or colours. This light is a precious source to create
NASA Technical Reports Server (NTRS)
Hanasoge, Shravan M.; Duvall, Thomas L., Jr.; Sreenivasan, Katepalli R.
2012-01-01
Convection in the solar interior is thought to comprise structures at a continuum of scales, from large to small. This conclusion emerges from phenomenological studies and numerical simulations though neither covers the proper range of dynamical parameters of solar convection. In the present work, imaging techniques of time-distance helioseismology applied to observational data reveal no long-range order in the convective motion. We conservatively bound the associated velocity magnitudes, as a function of depth and the spherical-harmonic degree l to be 20-100 times weaker than prevailing estimates within the wavenumber band l < 60. The observationally constrained kinetic energy is approximately a thousandth of the theoretical prediction, suggesting the prevalence of an intrinsically different paradigm of turbulence. A fundamental question arises: what mechanism of turbulence transports the heat ux of a solar luminosity outwards? The Sun is seemingly a much faster rotator than previously thought, with advection dominated by Coriolis forces at scales l < 60.
The Sun and the Solar Wind Close to the Sun
NASA Technical Reports Server (NTRS)
Suess, Steven T.
1998-01-01
One of the benefits from the Ulysses, SOHO, and YOHKOH missions has been a strong stimulus to better understand the magnetohydrodynamic processes involved in coronal expansion. Three topics for which this has been especially true are described here. These are: (i) The observed constancy of the radial interplanetary magnetic field strength (as mapped to constant radius). (ii) The geometric spreading of coronal plumes and coronal holes, and the fate of plumes. (iii) The plasma Beta in streamers and the physics of streamer confinement.
Simplified variational principles for non-barotropic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Yahalom, Asher
2016-04-01
> Variational principles for magnetohydrodynamics were introduced by previous authors both in Lagrangian and Eulerian form. In this paper we introduce simpler Eulerian variational principles from which all the relevant equations of non-barotropic magnetohydrodynamics can be derived for certain field topologies. The variational principle is given in terms of five independent functions for non-stationary barotropic flows. This is less than the eight variables which appear in the standard equations of barotropic magnetohydrodynamics which are the magnetic field the velocity field , the entropy and the density .
Smart, passive sun facing surfaces
Hively, Lee M.
1996-01-01
An article adapted for selectively utilizing solar radiation comprises an absorptive surface and a reflective surface, the absorptive surface and the reflective surface oriented to absorb solar radiation when the sun is in a relatively low position, and to reflect solar radiation when the sun is in a relatively high position.
Smart, passive sun facing surfaces
Hively, L.M.
1996-04-30
An article adapted for selectively utilizing solar radiation comprises an absorptive surface and a reflective surface, the absorptive surface and the reflective surface oriented to absorb solar radiation when the sun is in a relatively low position, and to reflect solar radiation when the sun is in a relatively high position. 17 figs.
NASA Astrophysics Data System (ADS)
Basu, Sarbani
2016-12-01
The seismic study of the Sun and other stars offers a unique window into the interior of these stars. Thanks to helioseismology, we know the structure of the Sun to admirable precision. In fact, our knowledge is good enough to use the Sun as a laboratory. We have also been able to study the dynamics of the Sun in great detail. Helioseismic data also allow us to probe the changes that take place in the Sun as solar activity waxes and wanes. The seismic study of stars other than the Sun is a fairly new endeavour, but we are making great strides in this field. In this review I discuss some of the techniques used in helioseismic analyses and the results obtained using those techniques. I focus on results obtained with global helioseismology, i.e., the study of the Sun using its normal modes of oscillation. I also briefly touch upon asteroseismology, the seismic study of stars other than the Sun, and discuss how seismic data of others stars are interpreted.
Magnetohydrodynamic Modeling of the Jovian Magnetosphere
NASA Technical Reports Server (NTRS)
Walker, Raymond
2005-01-01
Under this grant we have undertaken a series of magnetohydrodynamic (MHD) simulation and data analysis studies to help better understand the configuration and dynamics of Jupiter's magnetosphere. We approached our studies of Jupiter's magnetosphere in two ways. First we carried out a number of studies using our existing MHD code. We carried out simulation studies of Jupiter s magnetospheric boundaries and their dependence on solar wind parameters, we studied the current systems which give the Jovian magnetosphere its unique configuration and we modeled the dynamics of Jupiter s magnetosphere following a northward turning of the interplanetary magnetic field (IMF). Second we worked to develop a new simulation code for studies of outer planet magnetospheres.
Ideal magnetohydrodynamic stability of the spheromak configuration
Jardin, S.C.
1982-01-19
Results are presented of a parametric study of the ideal magnetohydrodynamic stability properties of the spheromak, or compact torus, configuration. In the absence of a nearby conducting wall, the spheromak is always unstable to at least one current driven mode. With a conducting wall at the surface, the spheromak can be unstable to current driven modes if the current is too peaked, i.e., q/sub o/(R/a) less than or equal to 2/3, or if the shear is too low at the origin. The Mercier criterion sets an upper limit on the pressure gradient everywhere, but configurations that are everywhere Mercier stable can be unstable to pressure driven low-n modes. Stable toroidal configurations exist with a spherical wall separated by half a minor radius, and with ..beta../sub theta/ = 30%.
Hall magneto-hydrodynamics in protoplanetary discs
NASA Astrophysics Data System (ADS)
Béthune, W.; Lesur, G.; Ferreira, J.
2016-12-01
Protoplanetary discs exhibit large-scale, organised structures. Because they are dense and cold, they should be weakly ionized, and hence concerned by non-ideal plasma effects, such as the Hall effect. We perform numerical simulations of non-stratified Keplerian discs, in the non-ideal magnetohydrodynamic framework. We show that the Hall effect causes self-organisation through three distinct stages. A weak Hall effect enhances turbulent transport. At intermediate strength, it produces magnetized vortices. A strong Hall effect generates axisymmetric zonal flows. These structures may trap dust particles, and thus influence planetary formation. The transport of angular momentum is quenched in the organised state, impugning the relevance of magneto-rotational turbulence as a driving mechanism of accretion in Hall dominated regions.
Exploring Astrophysical Magnetohydrodynamics in the Laboratory
NASA Astrophysics Data System (ADS)
Manuel, Mario
2014-10-01
Plasma evolution in many astrophysical systems is dominated by magnetohydrodynamics. Specifically of interest to this talk are collimated outflows from accretion systems. Away from the central object, the Euler equations can represent the plasma dynamics well and may be scaled to a laboratory system. We have performed experiments to investigate the effects of a background magnetic field on an otherwise hydrodynamically collimated plasma. Laser-irradiated, cone targets produce hydrodynamically collimated plasma jets and a pulse-powered solenoid provides a constant background magnetic field. The application of this field is shown to completely disrupt the original flow and a new magnetically-collimated, hollow envelope is produced. Results from these experiments and potential implications for their astrophysical analogs will be discussed.
Geometrical shock dynamics of fast magnetohydrodynamic shocks
NASA Astrophysics Data System (ADS)
Mostert, Wouter; Pullin, Dale I.; Samtaney, Ravi; Wheatley, Vincent
2016-11-01
We extend the theory of geometrical shock dynamics (GSD, Whitham 1958), to two-dimensional fast magnetohydrodynamic (MHD) shocks moving in the presence of nonuniform magnetic fields of general orientation and strength. The resulting generalized area-Mach number rule is adapted to MHD shocks moving in two spatial dimensions. A partially-spectral numerical scheme developed from that of Schwendeman (1993) is described. This is applied to the stability of plane MHD fast shocks moving into a quiescent medium containing a uniform magnetic field whose field lines are inclined to the plane-shock normal. In particular, we consider the time taken for an initially planar shock subject to an initial perturbed magnetosonic Mach number distribution, to first form shock-shocks. Supported by KAUST OCRF Award No. URF/1/2162-01.
Lagrangian simulation of explosively driven magnetohydrodynamic generator
NASA Astrophysics Data System (ADS)
Kim, Deok-Kyu; Seo, Min Su; Kim, Inho
2003-06-01
A series of time-dependent one-dimensional simulations has been carried out on the hydrodynamic behavior of argon and air plasmas in an explosively driven magnetohydrodynamic power generator. The thermodynamic properties of plasma gases are computed using equation-of-state data obtained from a detailed theoretical model. The plasma conductivities are given by a mixture rule, which comprises the fully and weakly ionized plasma approximations. The effects of the initial pressure and the magnetic field strength on the plasma behavior in the flow channel are examined over a moderate range of operating conditions, and then the computed results are compared with the experimental measurements, showing good agreement for the case of low magnetic Reynolds number.
Rarefaction wave in relativistic steady magnetohydrodynamic flows
Sapountzis, Konstantinos Vlahakis, Nektarios
2014-07-15
We construct and analyze a model of the relativistic steady-state magnetohydrodynamic rarefaction that is induced when a planar symmetric flow (with one ignorable Cartesian coordinate) propagates under a steep drop of the external pressure profile. Using the method of self-similarity, we derive a system of ordinary differential equations that describe the flow dynamics. In the specific limit of an initially homogeneous flow, we also provide analytical results and accurate scaling laws. We consider that limit as a generalization of the previous Newtonian and hydrodynamic solutions already present in the literature. The model includes magnetic field and bulk flow speed having all components, whose role is explored with a parametric study.
Nonideal magnetohydrodynamic instabilities and toroidal magnetic confinement
Furth, H.P.
1985-05-01
The marked divergence of experimentally observed plasma instability phenomena from the predictions of ideal magnetohydrodynamics led in the early 1960s to the formulations of finite-resistivity stability theory. Beginning in the 1970s, advanced plasma diagnostics have served to establish a detailed correspondence between the predictions of the finite-resistivity theory and experimental plasma behavior - particularly in the case of the resistive kink mode and the tokamak plasma. Nonlinear resistive-kink phenomena have been found to govern the transport of magnetic flux and plasma energy in the reversed-field pinch. The other predicted finite-resistivity instability modes have been more difficult to identify directly and their implications for toroidal magnetic confinement are still unresolved.
On the kinetic foundations of Kaluza's magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Sandoval-Villalbazo, Alfredo; Sagaceta-Mejía, Alma R.; García-Perciante, Ana L.
2015-06-01
Recent work has shown the existence of a relativistic effect present in a single component non-equilibrium fluid, corresponding to a heat flux due to an electric field [J. Non-Equilib. Thermodyn. 38 (2013), 141-151]. The treatment in that work was limited to a four-dimensional Minkowski space-time in which the Boltzmann equation was treated in a special relativistic approach. The more complete framework of general relativity can be introduced to kinetic theory in order to describe transport processes associated to electromagnetic fields. In this context, the original Kaluza's formalism is a promising approach [Sitz. Ber. Preuss. Akad. Wiss. (1921), 966-972; Gen. Rel. Grav. 39 (2007), 1287-1296; Phys. Plasmas 7 (2000), 4823-4830]. The present work contains a kinetic theory basis for Kaluza's magnetohydrodynamics and gives a novel description for the establishment of thermodynamic forces beyond the special relativistic description.
RESISTIVE MAGNETOHYDRODYNAMIC SIMULATIONS OF RELATIVISTIC MAGNETIC RECONNECTION
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2010-06-20
Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvenic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the 'diamond-chain' structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.
Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection
NASA Technical Reports Server (NTRS)
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2010-01-01
Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv enic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.
Action principles for extended magnetohydrodynamic models
NASA Astrophysics Data System (ADS)
Keramidas Charidakos, I.; Lingam, M.; Morrison, P. J.; White, R. L.; Wurm, A.
2014-09-01
The general, non-dissipative, two-fluid model in plasma physics is Hamiltonian, but this property is sometimes lost or obscured in the process of deriving simplified (or reduced) two-fluid or one-fluid models from the two-fluid equations of motion. To ensure that the reduced models are Hamiltonian, we start with the general two-fluid action functional, and make all the approximations, changes of variables, and expansions directly within the action context. The resulting equations are then mapped to the Eulerian fluid variables using a novel nonlocal Lagrange-Euler map. Using this method, we recover Lüst's general two-fluid model, extended magnetohydrodynamic (MHD), Hall MHD, and electron MHD from a unified framework. The variational formulation allows us to use Noether's theorem to derive conserved quantities for each symmetry of the action.
Remarkable connections between extended magnetohydrodynamics models
Lingam, M. Morrison, P. J. Miloshevich, G.
2015-07-15
Through the use of suitable variable transformations, the commonality of all extended magnetohydrodynamics (MHD) models is established. Remarkable correspondences between the Poisson brackets of inertialess Hall MHD and inertial MHD (which has electron inertia, but not the Hall drift) and extended MHD (which has both effects) are established. The helicities (two in all) for each of these models are obtained through these correspondences. The commonality of all the extended MHD models is traced to the existence of two Lie-dragged 2-forms, which are closely associated with the canonical momenta of the two underlying species. The Lie-dragging of these 2-forms by suitable velocities also leads to the correct equations of motion. The Hall MHD Poisson bracket is analyzed in detail, the Jacobi identity is verified through a detailed proof, and this proof ensures the Jacobi identity for the Poisson brackets of all the models.
A photolithographic fabrication technique for magnetohydrodynamic micropumps
NASA Astrophysics Data System (ADS)
Kuenstner, Stephen; Baylor, Martha-Elizabeth
2014-03-01
Magnetohydrodynamic (MHD) devices use perpendicular electric and magnetic fields to exert a Lorentz body force on a conducting fluid. Miniaturized MHD devices have been used to create pumps, stirrers, heat exchangers, and microfluidic networks. Compared to mechanical micropumps, MHD micropumps are appealing because they require no moving parts, which simplifies fabrication, and because they are amenable to electronic control. This abstract reports the fabrication and testing of a centimeter-scale MHD pump using a thiol-ene/methacrylate-based photopolymer and mask-based photolithographic technique. Pumps like this one could simplify the fabrication of sophisticated optofluidic devices, including liquid-core, liquid cladding (L2) waveguides, which are usually created with PDMS using stamps, or etched into silicon wafers. The photolithographic technique demonstrated here requires only one masking step to create fluid channels with complex geometries.
Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection
NASA Astrophysics Data System (ADS)
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2010-06-01
Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten-Lan-van Leer method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfvénic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond-chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet-Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.
Multidimensional numerical scheme for resistive relativistic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Komissarov, Serguei S.
2007-12-01
The paper describes a new upwind conservative numerical scheme for special relativistic resistive magnetohydrodynamics with scalar resistivity. The magnetic field is kept approximately divergence free and the divergence of the electric field is kept consistent with the electric charge distribution via the method of Generalized Lagrange Multiplier. The hyperbolic fluxes are computed using the Harten-Lax-van Leer (HLL) prescription and the source terms are accounted via the time-splitting technique. The results of test simulations show that the scheme can handle equally well both resistive current sheets and shock waves, and thus can be a useful tool for studying phenomena of relativistic astrophysics that involve both colliding supersonic flows and magnetic reconnection.
Numerical Methods for Radiation Magnetohydrodynamics in Astrophysics
Klein, R I; Stone, J M
2007-11-20
We describe numerical methods for solving the equations of radiation magnetohydrodynamics (MHD) for astrophysical fluid flow. Such methods are essential for the investigation of the time-dependent and multidimensional dynamics of a variety of astrophysical systems, although our particular interest is motivated by problems in star formation. Over the past few years, the authors have been members of two parallel code development efforts, and this review reflects that organization. In particular, we discuss numerical methods for MHD as implemented in the Athena code, and numerical methods for radiation hydrodynamics as implemented in the Orion code. We discuss the challenges introduced by the use of adaptive mesh refinement in both codes, as well as the most promising directions for future developments.
Ideal magnetohydrodynamic interchanges in low density plasmas
Huang Yimin; Goel, Deepak; Hassam, A.B.
2005-03-01
The ideal magnetohydrodynamic equations are usually derived under the assumption V{sub A}<
Numerical models for high beta magnetohydrodynamic flow
Brackbill, J.U.
1987-01-01
The fundamentals of numerical magnetohydrodynamics for highly conducting, high-beta plasmas are outlined. The discussions emphasize the physical properties of the flow, and how elementary concepts in numerical analysis can be applied to the construction of finite difference approximations that capture these features. The linear and nonlinear stability of explicit and implicit differencing in time is examined, the origin and effect of numerical diffusion in the calculation of convective transport is described, and a technique for maintaining solenoidality in the magnetic field is developed. Many of the points are illustrated by numerical examples. The techniques described are applicable to the time-dependent, high-beta flows normally encountered in magnetically confined plasmas, plasma switches, and space and astrophysical plasmas. 40 refs.
Acceleration of particles in imbalanced magnetohydrodynamic turbulence.
Teaca, Bogdan; Weidl, Martin S; Jenko, Frank; Schlickeiser, Reinhard
2014-08-01
The present work investigates the acceleration of test particles, relevant to the solar-wind problem, in balanced and imbalanced magnetohydrodynamic turbulence (terms referring here to turbulent states possessing zero and nonzero cross helicity, respectively). These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and nonresonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behavior is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating.
Structures in magnetohydrodynamic turbulence: Detection and scaling
NASA Astrophysics Data System (ADS)
Uritsky, V. M.; Pouquet, A.; Rosenberg, D.; Mininni, P. D.; Donovan, E. F.
2010-11-01
We present a systematic analysis of statistical properties of turbulent current and vorticity structures at a given time using cluster analysis. The data stem from numerical simulations of decaying three-dimensional magnetohydrodynamic turbulence in the absence of an imposed uniform magnetic field; the magnetic Prandtl number is taken equal to unity, and we use a periodic box with grids of up to 15363 points and with Taylor Reynolds numbers up to 1100. The initial conditions are either an X -point configuration embedded in three dimensions, the so-called Orszag-Tang vortex, or an Arn’old-Beltrami-Childress configuration with a fully helical velocity and magnetic field. In each case two snapshots are analyzed, separated by one turn-over time, starting just after the peak of dissipation. We show that the algorithm is able to select a large number of structures (in excess of 8000) for each snapshot and that the statistical properties of these clusters are remarkably similar for the two snapshots as well as for the two flows under study in terms of scaling laws for the cluster characteristics, with the structures in the vorticity and in the current behaving in the same way. We also study the effect of Reynolds number on cluster statistics, and we finally analyze the properties of these clusters in terms of their velocity-magnetic-field correlation. Self-organized criticality features have been identified in the dissipative range of scales. A different scaling arises in the inertial range, which cannot be identified for the moment with a known self-organized criticality class consistent with magnetohydrodynamics. We suggest that this range can be governed by turbulence dynamics as opposed to criticality and propose an interpretation of intermittency in terms of propagation of local instabilities.
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2016-05-01
Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward
Viscosity and Vorticity in Reduced Magneto-Hydrodynamics
Joseph, Ilon
2015-08-12
Magneto-hydrodynamics (MHD) critically relies on viscous forces in order for an accurate determination of the electric eld. For each charged particle species, the Braginskii viscous tensor for a magnetized plasma has the decomposition into matrices with special symmetries.
An AC magnetohydrodynamic micropump: towards a true integrated microfluidic system
Lee, A P; Lemoff, A V; McConaghy, C F; Miles, R R
1999-03-01
An AC Magnetohydrodynamic (MHD) micropump has been demonstrated in which the Lorentz force is used to propel an electrolytic solution along a microchannel etched in silicon. This micropump has no moving parts, produces a continuous (not pulsatile) flow, and is compatible with solutions containing biological specimens. micropump, using the Lorentz force as the pumping mechanism for biological analysis. The AC Magnetohydrodynamic (MHD) micropump investigated produces a continuous flow and allows for complex microchannel design.
Dislocations in magnetohydrodynamic waves in a stellar atmosphere.
López Ariste, A; Collados, M; Khomenko, E
2013-08-23
We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots.
Government research and development summaries: Magnetohydrodynamic project briefs. Irregular
1995-03-01
Magnetohydrodynamic Project Briefs describe the status of all R and D programs submitted to the Power Information Center by the government sponsors in energy conversion involving the magnetohydrodynamic (MHD) interaction between electromagnetic fields and electrically conducting fields, including fuels, materials, plasma dynamics, and combustion. The document is not to be reproduced, in whole or in part, for dissemination outside your own organization nor may it be reproduced for advertising or sales promotion purposes.
Magnetohydrodynamic Augmentation of Pulse Detonation Rocket Engines (Preprint)
2010-09-28
system will either be over- or under-expanded for the majority of the cycle , with en- ergy being used without maximum gain. Magnetohydrodynamic ( MHD ...to their potentially superior performance over constant pressure cycle engines. Yet due to its unsteady chamber pressure, the PDE system will either...be over- or under-expanded for the majority of the cycle , with energy being used without maximum gain. Magnetohydrodynamic ( MHD ) augmentation offers
Government research and development summaries: Magnetohydrodynamic project briefs. Irregular
Not Available
1994-01-01
Magnetohydrodynamic Project Briefs describe the status of all R and D programs submitted to the Power Information Center by the government sponsors in energy conversion involving the magnetohydrodynamic (MHD) interaction between electromagnetic fields and electrically conducting fields, including fuels, materials, plasma dynamics, and combustion. The document is not to be reproduced, in whole or in part, for dissemination outside your own organization nor may it be reproduced for advertising or sales promotion purposes.
NASA Astrophysics Data System (ADS)
Pesnell, W. Dean
2016-07-01
Space-based solar observatories have made fundamental discoveries about the lifecycle of the solar magnetic field and how that field affects the solar system. Observing the Sun from space provides access to all wavelengths of light and eliminates the smearing of atmospheric seeing. Being in space means the emissions from the highly-ionized material that are the natural emissions of the corona can be measured. Continuous observations of the Sun can be made from a single satellite in certain orbits. This leads to unexpected discoveries, such as orbiting coronagraphs showing that sun grazing comets are the most common class of observed comets. Or when the coronal holes discovered with the solar X-ray telescopes on Skylab explained long-noticed correlations in particle fluxes from the Sun with solar longitudes. Space-based coronagraphs and heliospheric imagers are able to track coronal mass ejections from when they leave the Sun until they hit the Earth or another planet. In a more practical point, as humans have become more entwined in the use of technology, the magnetic field of the Sun has become more intrusive. Energetic particles and high-energy photons from solar fares can compromise humans and electronics in space. As a coronal mass ejection passes by and interacts with the Earth's magnetosphere, it generates large currents at the Earth's surface that can disrupt power distribution systems. The measurements of Sun made possible by being in space will be described, along with some highlights of the observatories that make them.
NASA Technical Reports Server (NTRS)
2004-01-01
This animation shows the passing, or transit, of the martian moon Deimos over the Sun. This event is similar solar eclipse seen on Earth in which our Moon crosses in front of the Sun. The animation is made up of images taken by the Mars Exploration Rover Opportunity on sol 39 of its mission. Deimos passed slightly closer to the center of the Sun than expected, and arrived about 30 seconds early. This observation will help refine our knowledge of the orbit and position of Deimos.
Sun Tracking Systems: A Review
Lee, Chia-Yen; Chou, Po-Cheng; Chiang, Che-Ming; Lin, Chiu-Feng
2009-01-01
The output power produced by high-concentration solar thermal and photovoltaic systems is directly related to the amount of solar energy acquired by the system, and it is therefore necessary to track the sun's position with a high degree of accuracy. Many systems have been proposed to facilitate this task over the past 20 years. Accordingly, this paper commences by providing a high level overview of the sun tracking system field and then describes some of the more significant proposals for closed-loop and open-loop types of sun tracking systems. PMID:22412341
Sun tracking systems: a review.
Lee, Chia-Yen; Chou, Po-Cheng; Chiang, Che-Ming; Lin, Chiu-Feng
2009-01-01
The output power produced by high-concentration solar thermal and photovoltaic systems is directly related to the amount of solar energy acquired by the system, and it is therefore necessary to track the sun's position with a high degree of accuracy. Many systems have been proposed to facilitate this task over the past 20 years. Accordingly, this paper commences by providing a high level overview of the sun tracking system field and then describes some of the more significant proposals for closed-loop and open-loop types of sun tracking systems.
1993-01-01
COVER FEATURE Brazil: Colossus of the Sun By United States Military Liaison Office Team [Editor’s Note. The following report continues our series...residents of the Colossus of the Sun , as Brazil has come to be known, enjoy tropical weather, maritime breezes, and exciting beaches. Over 90 percent of...DATE 1993 2. REPORT TYPE 3. DATES COVERED 00-00-1993 to 00-00-1993 4. TITLE AND SUBTITLE Brazil: Colossus of the Sun 5a. CONTRACT NUMBER 5b
A Global Magnetohydrodynamic Model of Jovian Magnetosphere
NASA Technical Reports Server (NTRS)
Walker, Raymond J.; Sharber, James (Technical Monitor)
2001-01-01
The goal of this project was to develop a new global magnetohydrodynamic model of the interaction of the Jovian magnetosphere with the solar wind. Observations from 28 orbits of Jupiter by Galileo along with those from previous spacecraft at Jupiter, Pioneer 10 and 11, Voyager I and 2 and Ulysses, have revealed that the Jovian magnetosphere is a vast, complicated system. The Jovian aurora also has been monitored for several years. Like auroral observations at Earth, these measurements provide us with a global picture of magnetospheric dynamics. Despite this wide range of observations, we have limited quantitative understanding of the Jovian magnetosphere and how it interacts with the solar wind. For the past several years we have been working toward a quantitative understanding of the Jovian magnetosphere and its interaction with the solar wind by employing global magnetohydrodynamic simulations to model the magnetosphere. Our model has been an explicit MHD code (previously used to model the Earth's magnetosphere) to study Jupiter's magnetosphere. We continue to obtain important insights with this code, but it suffers from some severe limitations. In particular with this code we are limited to considering the region outside of 15RJ, with cell sizes of about 1.5R(sub J). The problem arises because of the presence of widely separated time scales throughout the magnetosphere. The numerical stability criterion for explicit MHD codes is the CFL limit and is given by C(sub max)(Delta)t/(Delta)x less than 1 where C(sub max) is the maximum group velocity in a given cell, (Delta)x is the grid spacing and (Delta)t is the time step. If the maximum wave velocity is C(sub w) and the flow speed is C(sub f), C(sub max) = C(sub w) + C(sub f). Near Jupiter the Alfven wave speed becomes very large (it approaches the speed of light at one Jovian radius). Operating with this time step makes the calculation essentially intractable. Therefore under this funding we have been designing a
Converging cylindrical shocks in ideal magnetohydrodynamics
Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.
2014-09-15
We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R=√(μ{sub 0}/p{sub 0}) I/(2 π) where I is the current, μ{sub 0} is the permeability, and p{sub 0} is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The
Converging cylindrical shocks in ideal magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.
2014-09-01
We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also of a parameter measuring the local strength of the magnetic field. For the line current case, two approaches are explored and the results compared in detail. The first is geometrical shock-dynamics where the restricted shock-jump conditions are applied directly to the equation on the characteristic entering the shock from behind. This gives an ordinary-differential equation for the shock Mach number as a function of radius which is integrated numerically to provide profiles of the shock implosion. Also, analytic, asymptotic results are obtained for the shock trajectory at small radius. The second approach is direct numerical solution of the radially symmetric MHD equations using a shock-capturing method. For the axial magnetic field case the shock implosion is of the Guderley power-law type with exponent that is not affected by the presence of a finite magnetic field. For the axial current case, however, the presence of a tangential magnetic field ahead of the shock with strength inversely proportional to radius introduces a length scale R=sqrt{μ _0/p_0} I/(2 π ) where I is the current, μ0 is the permeability, and p0 is the pressure ahead of the shock. For shocks initiated at r ≫ R, shock convergence is first accompanied by shock strengthening as for the strictly gas-dynamic implosion. The diverging magnetic field
The X-ray Telescope on the Japanese/NASA mission Hinode has been observing the full sun, nearly continuously, for an extended period. In this movie significant small-scale dynamic events can be obs...
Prototype of sun projector device
NASA Astrophysics Data System (ADS)
Ihsan; Dermawan, B.
2016-11-01
One way to introduce astronomy to public, including students, can be handled by solar observation. The widely held device for this purpose is coelostat and heliostat. Besides using filter attached to a device such as telescope, it is safest to use indirect way for observing the Sun. The main principle of the indirect way is deflecting the sun light and projecting image of the sun on a screen. We design and build a simple and low-cost astronomical device, serving as a supplement to increase public service, especially for solar observation. Without using any digital and intricate supporting equipment, people can watch and relish image of the Sun in comfortable condition, i.e. in a sheltered or shady place. Here we describe a design and features of our prototype of the device, which still, of course, has some limitations. In the future, this prototype can be improved for more efficient and useful applications.
Le, Minh; Resch, Rhone
2016-07-12
Highlights of the SunShot program, the national targets for the program, and the "all of the above" approach to achieving those goals through research, tech transfer, permitting, tax incentives, and a comprehensive approach to installation.
This video from NASA's Solar Dynamics Observatory spacecraft, orbiting more than 20,000 miles above Earth, shows a stream of plasma burst out from the sun on May 27,2014. Since the stream lacked en...
Le, Minh; Resch, Rhone
2014-05-19
Highlights of the SunShot program, the national targets for the program, and the "all of the above" approach to achieving those goals through research, tech transfer, permitting, tax incentives, and a comprehensive approach to installation.
Change in the Radiative Output of the Sun in 1992 and Its Effect in the Thermosphere
1994-01-01
months of 1992. This sustained drop in the solar output is important in understanding the connection between the emergent magnetic flux on the Sun and the...progress indicates that the output change results from the decline in solar magnetic flux to a lower level of activity in the southern hemisphere of the Sun .
Sun safety knowledge and practice in UK postal delivery workers
Davis, S.; Griffiths, A.
2016-01-01
Background Postal delivery workers spend a large proportion of their work time outdoors, placing them at increased risk of skin cancer. To date, no studies have examined occupational sun safety knowledge and practice within this group in the UK. Aims To describe the occupational sun safety knowledge and practice of UK postal delivery workers and to investigate the association of demographic, personal and occupational factors with knowledge and practice in order to identify potential strategies for improving sun safety in this occupational group. Methods Postal delivery workers completed a questionnaire that collected data on occupational sun safety knowledge and practice in addition to demographic, personal and workplace characteristics. One-way analysis of variances were applied to assess differences in knowledge and practice by these characteristics. Results A total of 1153 postal delivery workers completed the questionnaire, a 60% response rate. Thirty-three per cent reported receiving sun safety training within the previous 12 months. The majority of respondents reported correct knowledge on three of the six domains and good practice on four of the six behavioural domains. However, only one-fifth of respondents reported wearing sunglasses and ensuring a plentiful intake of water. Knowledge and practice differed significantly according to demographic, personal and workplace characteristics. Conclusions There is a need to raise the profile of occupational skin cancer in this occupational group and to increase the priority given to occupational sun safety policies alongside targeted and tailored interventions, the effect of which can be evaluated. PMID:26675005
The role of the magnetorotational instability in the sun
Kagan, Daniel; Wheeler, J. Craig E-mail: wheel@astro.as.utexas.edu
2014-05-20
We calculate growth rates for nonaxisymmetric instabilities including the magnetorotational instability (MRI) throughout the Sun. We first derive a dispersion relation for nonaxisymmetric instability including the effects of shear, convective buoyancy, and three diffusivities (thermal conductivity, resistivity, and viscosity). We then use a solar model evolved with the stellar evolution code MESA and angular velocity profiles determined by Global Oscillations Network Group helioseismology to determine the unstable modes present at each location in the Sun and the associated growth rates. The overall instability has unstable modes throughout the convection zone and also slightly below it at middle and high latitudes. It contains three classes of modes: large-scale hydrodynamic convective modes, large-scale hydrodynamic shear modes, and small-scale magnetohydrodynamic shear modes, which may be properly called MRI modes. While large-scale convective modes are the most rapidly growing modes in most of the convective zone, MRI modes are important in both stably stratified and convectively unstable locations near the tachocline at colatitudes θ < 53°. Nonaxisymmetric MRI modes grow faster than the corresponding axisymmetric modes; for some poloidal magnetic fields, the nonaxisymmetric MRI growth rates are similar to the angular rotation frequency Ω, while axisymmetric modes are stabilized. We briefly discuss the saturation of the field produced by MRI modes, finding that the implied field at the base of the convective zone in the Sun is comparable to that derived based on dynamos active in the tachocline and that the saturation of field resulting from the MRI may be of importance even in the upper convection zone.
Lattice Boltzmann model for resistive relativistic magnetohydrodynamics.
Mohseni, F; Mendoza, M; Succi, S; Herrmann, H J
2015-08-01
In this paper, we develop a lattice Boltzmann model for relativistic magnetohydrodynamics (MHD). Even though the model is derived for resistive MHD, it is shown that it is numerically robust even in the high conductivity (ideal MHD) limit. In order to validate the numerical method, test simulations are carried out for both ideal and resistive limits, namely the propagation of Alfvén waves in the ideal MHD and the evolution of current sheets in the resistive regime, where very good agreement is observed comparing to the analytical results. Additionally, two-dimensional magnetic reconnection driven by Kelvin-Helmholtz instability is studied and the effects of different parameters on the reconnection rate are investigated. It is shown that the density ratio has a negligible effect on the magnetic reconnection rate, while an increase in shear velocity decreases the reconnection rate. Additionally, it is found that the reconnection rate is proportional to σ-1/2, σ being the conductivity, which is in agreement with the scaling law of the Sweet-Parker model. Finally, the numerical model is used to study the magnetic reconnection in a stellar flare. Three-dimensional simulation suggests that the reconnection between the background and flux rope magnetic lines in a stellar flare can take place as a result of a shear velocity in the photosphere.
Imbalanced relativistic force-free magnetohydrodynamic turbulence
Cho, Jungyeon; Lazarian, A.
2014-01-01
When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfvénic MHD turbulence in the relativistic limit can be described by interactions of counter-traveling wave packets. In this paper, we numerically study strong imbalanced MHD turbulence in such environments. Here, imbalanced turbulence means the waves traveling in one direction (dominant waves) have higher amplitudes than the opposite-traveling waves (sub-dominant waves). We find that (1) spectrum of the dominant waves is steeper than that of sub-dominant waves, (2) the anisotropy of the dominant waves is weaker than that of sub-dominant waves, and (3) the dependence of the ratio of magnetic energy densities of dominant and sub-dominant waves on the ratio of energy injection rates is steeper than quadratic (i.e., b{sub +}{sup 2}/b{sub −}{sup 2}∝(ϵ{sub +}/ϵ{sub −}){sup n} with n > 2). These results are consistent with those obtained for imbalanced non-relativistic Alfvénic turbulence. This corresponds well to the earlier reported similarity of the relativistic and non-relativistic balanced magnetic turbulence.
Large-scale quasi-geostrophic magnetohydrodynamics
Balk, Alexander M.
2014-12-01
We consider the ideal magnetohydrodynamics (MHD) of a shallow fluid layer on a rapidly rotating planet or star. The presence of a background toroidal magnetic field is assumed, and the 'shallow water' beta-plane approximation is used. We derive a single equation for the slow large length scale dynamics. The range of validity of this equation fits the MHD of the lighter fluid at the top of Earth's outer core. The form of this equation is similar to the quasi-geostrophic (Q-G) equation (for usual ocean or atmosphere), but the parameters are essentially different. Our equation also implies the inverse cascade; but contrary to the usual Q-G situation, the energy cascades to smaller length scales, while the enstrophy cascades to the larger scales. We find the Kolmogorov-type spectrum for the inverse cascade. The spectrum indicates the energy accumulation in larger scales. In addition to the energy and enstrophy, the obtained equation possesses an extra (adiabatic-type) invariant. Its presence implies energy accumulation in the 30° sector around zonal direction. With some special energy input, the extra invariant can lead to the accumulation of energy in zonal magnetic field; this happens if the input of the extra invariant is small, while the energy input is considerable.
Global invariants in ideal magnetohydrodynamic turbulence
Shebalin, John V.
2013-10-15
Magnetohydrodynamic (MHD) turbulence is an important though incompletely understood factor affecting the dynamics of many astrophysical, geophysical, and technological plasmas. As an approximation, viscosity and resistivity may be ignored, and ideal MHD turbulence may be investigated by statistical methods. Incompressibility is also assumed and finite Fourier series are used to represent the turbulent velocity and magnetic field. The resulting model dynamical system consists of a set of independent Fourier coefficients that form a canonical ensemble described by a Gaussian probability density function (PDF). This PDF is similar in form to that of Boltzmann, except that its argument may contain not just the energy multiplied by an inverse temperature, but also two other invariant integrals, the cross helicity and magnetic helicity, each multiplied by its own inverse temperature. However, the cross and magnetic helicities, as usually defined, are not invariant in the presence of overall rotation or a mean magnetic field, respectively. Although the generalized form of the magnetic helicity is known, a generalized cross helicity may also be found, by adding terms that are linear in the mean magnetic field and angular rotation vectors, respectively. These general forms are invariant even in the presence of overall rotation and a mean magnetic field. We derive these general forms, explore their properties, examine how they extend the statistical theory of ideal MHD turbulence, and discuss how our results may be affected by dissipation and forcing.
NIMROD resistive magnetohydrodynamic simulations of spheromak physics
NASA Astrophysics Data System (ADS)
Hooper, E. B.; Cohen, B. I.; McLean, H. S.; Wood, R. D.; Romero-Talamás, C. A.; Sovinec, C. R.
2008-03-01
The physics of spheromak plasmas is addressed by time-dependent, three-dimensional, resistive magnetohydrodynamic simulations with the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. Included in some detail are the formation of a spheromak driven electrostatically by a coaxial plasma gun with a flux-conserver geometry and power systems that accurately model the sustained spheromak physics experiment [R. D. Wood et al., Nucl. Fusion 45, 1582 (2005)]. The controlled decay of the spheromak plasma over several milliseconds is also modeled as the programmable current and voltage relax, resulting in simulations of entire experimental pulses. Reconnection phenomena and the effects of current profile evolution on the growth of symmetry-breaking toroidal modes are diagnosed; these in turn affect the quality of magnetic surfaces and the energy confinement. The sensitivity of the simulation results addresses variations in both physical and numerical parameters, including spatial resolution. There are significant points of agreement between the simulations and the observed experimental behavior, e.g., in the evolution of the magnetics and the sensitivity of the energy confinement to the presence of symmetry-breaking magnetic fluctuations.
COUNTER-ROTATION IN RELATIVISTIC MAGNETOHYDRODYNAMIC JETS
Cayatte, V.; Sauty, C.; Vlahakis, N.; Tsinganos, K.; Matsakos, T.; Lima, J. J. G.
2014-06-10
Young stellar object observations suggest that some jets rotate in the opposite direction with respect to their disk. In a recent study, Sauty et al. showed that this does not contradict the magnetocentrifugal mechanism that is believed to launch such outflows. Motion signatures that are transverse to the jet axis, in two opposite directions, have recently been measured in M87. One possible interpretation of this motion is that of counter-rotating knots. Here, we extend our previous analytical derivation of counter-rotation to relativistic jets, demonstrating that counter-rotation can indeed take place under rather general conditions. We show that both the magnetic field and a non-negligible enthalpy are necessary at the origin of counter-rotating outflows, and that the effect is associated with a transfer of energy flux from the matter to the electromagnetic field. This can be realized in three cases: if a decreasing enthalpy causes an increase of the Poynting flux, if the flow decelerates, or if strong gradients of the magnetic field are present. An illustration of the involved mechanism is given by an example of a relativistic magnetohydrodynamic jet simulation.
Modeling eruptive coronal magnetohydrodynamic systems with FLUX
NASA Astrophysics Data System (ADS)
Rachmeler, L. A.
In this dissertation I explore solar coronal energetic eruptions in the context of magnetic reconnection, which is commonly thought to be a required trigger mechanism for solar eruptions. Reconnection is difficult to directly observe in the corona, and current numerical methods cannot model reconnectionless control cases. Thus, it is not possible to determine if reconnection is a necessary component of these eruptions. I have executed multiple controlled simulations to determine the importance of reconnection for initiation and evolution of several eruptive systems using FLUX, a numerical model that uses the comparatively new fluxon technique. I describe two types of eruptions modeled with FLUX: a metastable confined flux rope theory for coronal mass ejection (CME) initiation, and symmetrically twisted coronal jets in a uniform vertical background field. In the former, I identified an ideal magnetohydrodynamic (MHD) instability that allows metastable twisted flux rope systems to suddenly lose stability and erupt even in the absence of reconnection, contradicting previous conjecture. The CME result is in contrast to the azimuthally symmetric coronal jet initiation model, where jet-like behavior does not manifest without reconnection. My work has demonstrated that some of the observed eruptive phenomena may be triggered by non-reconnective means such as ideal MHD instabilities, and that magnetic reconnection is not a required element in all coronal eruptions.
INVERSE CASCADE IN IMBALANCED ELECTRON MAGNETOHYDRODYNAMIC TURBULENCE
Kim, Hoonkyu; Cho, Jungyeon E-mail: jcho@cnu.ac.kr
2015-03-10
Electron magnetohydrodynamics (EMHD) provides a fluid-like description of small-scale magnetized plasmas. Balanced EMHD turbulence has been studied for a long time. However, driven imbalanced EMHD turbulence, in which waves moving in one direction (dominant waves) have higher amplitudes than waves moving in the other direction (sub-dominant waves), has not been well studied. In this paper, we numerically study driven three-dimensional imbalanced weak EMHD turbulence. We find the following results. First, in driven imbalanced EMHD turbulence, we clearly observe inverse cascade of magnetic helicity, as well as magnetic energy. This is because magnetic helicity is a conserved quantity and non-zero magnetic helicity is injected into the system in driven imbalanced EMHD turbulence. Second, the magnetic energy spectrum of the dominant waves on scales larger than the energy injection scale does not show a single power-law spectrum, which indicates that the inverse cascade is not a self-similar process. The peak of the spectrum roughly follows a k {sup –3/2} spectrum, which can be explained by a Kolmogorov-type argument for weak turbulence. Third, a small amount of sub-dominant waves is induced by the dominant waves on large scales and the ratio of helicity densities of the dominant and the sub-dominant waves on large scales seems to converge to a certain value.
Energetic particle effects on global magnetohydrodynamic modes
NASA Astrophysics Data System (ADS)
Cheng, C. Z.
1990-06-01
The effects of energetic particles on magnetohydrodynamic (MHD) type modes are studied using analytical theories and the nonvariational kinetic-MHD stability code (nova-k) [Workshop on Theory of Fusion Plasmas, (Societa Italiana di Fisica, Bologna, 1987), p. 185]. In particular, the problems of (1) the stabilization of ideal MHD internal kink modes and the excitation of resonant ``fishbone'' internal modes and (2) the alpha particle destabilization of toroidicity-induced Alfvén eigenmodes (TAE) via transit resonances are addressed. Analytical theories are presented to help explain the nova-k results. For energetic trapped particles generated by neutral beam injection or ion cyclotron resonant heating, a stability window for the n=1 internal kink mode in the hot particle beta space exists even in the absence of core ion finite Larmor radius effect. On the other hand, the trapped alpha particles are found to resonantly excite instability of the n=1 internal mode and can lower the critical beta threshold. The circulating alpha particles can strongly destabilize TAE modes via inverse Landau damping associated with the spatial gradient of the alpha-particle pressure.
Lattice Boltzmann model for resistive relativistic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Mohseni, F.; Mendoza, M.; Succi, S.; Herrmann, H. J.
2015-08-01
In this paper, we develop a lattice Boltzmann model for relativistic magnetohydrodynamics (MHD). Even though the model is derived for resistive MHD, it is shown that it is numerically robust even in the high conductivity (ideal MHD) limit. In order to validate the numerical method, test simulations are carried out for both ideal and resistive limits, namely the propagation of Alfvén waves in the ideal MHD and the evolution of current sheets in the resistive regime, where very good agreement is observed comparing to the analytical results. Additionally, two-dimensional magnetic reconnection driven by Kelvin-Helmholtz instability is studied and the effects of different parameters on the reconnection rate are investigated. It is shown that the density ratio has a negligible effect on the magnetic reconnection rate, while an increase in shear velocity decreases the reconnection rate. Additionally, it is found that the reconnection rate is proportional to σ-1 / 2, σ being the conductivity, which is in agreement with the scaling law of the Sweet-Parker model. Finally, the numerical model is used to study the magnetic reconnection in a stellar flare. Three-dimensional simulation suggests that the reconnection between the background and flux rope magnetic lines in a stellar flare can take place as a result of a shear velocity in the photosphere.
Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab
NASA Astrophysics Data System (ADS)
Allcock, Matthew; Erdélyi, Robert
2017-02-01
Analytical models of solar atmospheric magnetic structures have been crucial for our understanding of magnetohydrodynamic (MHD) wave behaviour and in the development of the field of solar magneto-seismology. Here, an analytical approach is used to derive the dispersion relation for MHD waves in a magnetic slab of homogeneous plasma enclosed on its two sides by non-magnetic, semi-infinite plasma with different densities and temperatures. This generalises the classic magnetic slab model, which is symmetric about the slab. The dispersion relation, unlike that governing a symmetric slab, cannot be decoupled into the well-known sausage and kink modes, i.e. the modes have mixed properties. The eigenmodes of an asymmetric magnetic slab are better labelled as quasi-sausage and quasi-kink modes. Given that the solar atmosphere is highly inhomogeneous, this has implications for MHD mode identification in a range of solar structures. A parametric analysis of how the mode properties (in particular the phase speed, eigenfrequencies, and amplitudes) vary in terms of the introduced asymmetry is conducted. In particular, avoided crossings occur between quasi-sausage and quasi-kink surface modes, allowing modes to adopt different properties for different parameters in the external region.
Magnetohydrodynamic Origin of Jets from Accretion Disks
NASA Technical Reports Server (NTRS)
Lovelace, R. V. E.; Romanova, M. M.
1998-01-01
A review is made of magnetohydrodynamic (MHD) theory and simulation of outflows from disks for different distributions of magnetic field threading the disk. In one limit of a relatively weak, initially diverging magnetic field, both thermal and magnetic pressure gradients act to drive matter to an outflow, while a toroidal magnetic field develops which strongly collimates the outflow. The collimation greatly reduces the field divergence and the mass outflow rate decreases after an initial peak. In a second limit of a strong magnetic field, the initial field configuration was taken with the field strength on the disk decreasing outwards to small values so that collimation was reduced. As a result, a family of stationary solutions was discovered where matter is driven mainly by the strong magnetic pressure gradient force. The collimation in this case depends on the pressure of an external medium. These flows are qualitatively similar to the analytic solutions for magnetically driven outflows. The problem of the opening of a closed field line configuration linking a magnetized star and an accretion disk is also discussed.
Global invariants in ideal magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Shebalin, John V.
2013-10-01
Magnetohydrodynamic (MHD) turbulence is an important though incompletely understood factor affecting the dynamics of many astrophysical, geophysical, and technological plasmas. As an approximation, viscosity and resistivity may be ignored, and ideal MHD turbulence may be investigated by statistical methods. Incompressibility is also assumed and finite Fourier series are used to represent the turbulent velocity and magnetic field. The resulting model dynamical system consists of a set of independent Fourier coefficients that form a canonical ensemble described by a Gaussian probability density function (PDF). This PDF is similar in form to that of Boltzmann, except that its argument may contain not just the energy multiplied by an inverse temperature, but also two other invariant integrals, the cross helicity and magnetic helicity, each multiplied by its own inverse temperature. However, the cross and magnetic helicities, as usually defined, are not invariant in the presence of overall rotation or a mean magnetic field, respectively. Although the generalized form of the magnetic helicity is known, a generalized cross helicity may also be found, by adding terms that are linear in the mean magnetic field and angular rotation vectors, respectively. These general forms are invariant even in the presence of overall rotation and a mean magnetic field. We derive these general forms, explore their properties, examine how they extend the statistical theory of ideal MHD turbulence, and discuss how our results may be affected by dissipation and forcing.
Energetic particle effects on global magnetohydrodynamic modes
Cheng, C.Z. )
1990-06-01
The effects of energetic particles on magnetohydrodynamic (MHD) type modes are studied using analytical theories and the nonvariational kinetic-MHD stability code (NOVA-K) ({ital Workshop} {ital on} {ital Theory} {ital of} {ital Fusion} {ital Plasmas}, (Societa Italiana di Fisica, Bologna, 1987), p. 185). In particular, the problems of (1) the stabilization of ideal MHD internal kink modes and the excitation of resonant fishbone'' internal modes and (2) the alpha particle destabilization of toroidicity-induced Alfven eigenmodes (TAE) via transit resonances are addressed. Analytical theories are presented to help explain the NOVAresults. For energetic trapped particles generated by neutral beam injection or ion cyclotron resonant heating, a stability window for the {ital n}=1 internal kink mode in the hot particle beta space exists even in the absence of core ion finite Larmor radius effect. On the other hand, the trapped alpha particles are found to resonantly excite instability of the {ital n}=1 internal mode and can lower the critical beta threshold. The circulating alpha particles can strongly destabilize TAE modes via inverse Landau damping associated with the spatial gradient of the alpha-particle pressure.
Tomida, Kengo; Okuzumi, Satoshi; Machida, Masahiro N. E-mail: okuzumi@geo.titech.ac.jp
2015-03-10
The transport of angular momentum by magnetic fields is a crucial physical process in the formation and evolution of stars and disks. Because the ionization degree in star-forming clouds is extremely low, nonideal magnetohydrodynamic (MHD) effects such as ambipolar diffusion and ohmic dissipation work strongly during protostellar collapse. These effects have significant impacts in the early phase of star formation as they redistribute magnetic flux and suppress angular momentum transport by magnetic fields. We perform three-dimensional nested-grid radiation magnetohydrodynamic simulations including ohmic dissipation and ambipolar diffusion. Without these effects, magnetic fields transport angular momentum so efficiently that no rotationally supported disk is formed even after the second collapse. Ohmic dissipation works only in a relatively high density region within the first core and suppresses angular momentum transport, enabling formation of a very small rotationally supported disk after the second collapse. With both ohmic dissipation and ambipolar diffusion, these effects work effectively in almost the entire region within the first core and significant magnetic flux loss occurs. As a result, a rotationally supported disk is formed even before a protostellar core forms. The size of the disk is still small, about 5 AU at the end of the first core phase, but this disk will grow later as gas accretion continues. Thus, the nonideal MHD effects can resolve the so-called magnetic braking catastrophe while keeping the disk size small in the early phase, which is implied from recent interferometric observations.
De Freitas, D. B.; Leao, I. C.; Lopes, C. E. Ferreira; Paz-Chinchon, F.; Canto Martins, B. L.; Alves, S.; De Medeiros, J. R.; Catelan, M.
2013-08-20
The present work reports on the discovery of three stars that we have identified to be rotating Sun-like stars, based on rotational modulation signatures inferred from light curves from the CoRoT mission's Public Archives. In our analysis, we performed an initial selection based on the rotation period and position in the period-T{sub eff} diagram. This revealed that the stars CoRoT IDs 100746852, 102709980, and 105693572 provide potentially good matches to the Sun with a similar rotation period. To refine our analysis, we applied a novel procedure, taking into account the fluctuations of the features associated with photometric modulation at different time intervals and the fractality traces that are present in the light curves of the Sun and of these ''New Sun'' candidates alike. In this sense, we computed the so-called Hurst exponent for the referred stars, for a sample of 14 CoRoT stars with sub- and super-solar rotational periods, and for the Sun itself in its active and quiet phases. We found that the Hurst exponent can provide a strong discriminant of Sun-like behavior, going beyond what can be achieved with solely the rotation period itself. In particular, we find that CoRoT ID 105693572 is the star that most closely matches the solar rotation properties as far as the latter's imprints on light curve behavior are concerned. The stars CoRoT IDs 100746852 and 102709980 have significant smaller Hurst exponents than the Sun, notwithstanding their similarity in rotation periods.
Magnetohydrodynamic Modeling of Coronal Evolution and Disruption
NASA Technical Reports Server (NTRS)
Linker, Jon
2002-01-01
Flux cancellation, defined observationally as the mutual disappearance of magnetic fields of opposite polarity at the neutral line separating them, has been found to occur frequently at the site of filaments (called prominences when observed on the limb of the Sun). During the second year of this project, we have studied theoretically the role that flux cancellation may play in prominence formation, prominence eruption, and the initiation of coronal mass ejections. This work has been in published in two papers: "Magnetic Field Topology in Prominences" by Lionello, Mikic, Linker, and Amari and "Flux Cancellation and Coronal Mass Ejections" by Linker, Mikic, Riley, Lionello, Amari, and Odstrcil.
The Hot Outer Atmosphere of the Sun (June/July 2012)
The sun's hot outer atmosphere, as viewed by the Atmospheric Imaging Assembly (AIA) onboard NASA's Solar Dynamics Observatory. The movie shows one month of observations ending on the day of the Hi-...
A Solar Wind Short Distance Propagation Model Based on Magneto-Hydrodynamics
NASA Astrophysics Data System (ADS)
Kulchitsky, A.
2006-12-01
It is essential to know parameters of the Interplanetary Magnetic Field (IMF) and solar wind in the near Earth magnetosphere for research on the effects of the IMF in near-Earth space. Measurements of the IMF taken at the first Lagrange point (L_1) by the ACE space satellite, about 230 Earth Radii away, are typically used for estimation of IMF near the Earth. In many geophysical applications, it is assumed that we can use a simple kinematic approach to map the parameters measured at the satellite to the Earth by shifting them in time. The simple formula is to calculate the time delay as the distance from the Earth to the satellite divided by the velocity of the solar wind, projected along the Earth-Sun line. There are two important problems to be addressed with this simple kinematic approach. The first problem is that solar wind is not uniform and particles that hit the satellite often miss the Earth. Typically, the satellite is shifted by 30 or more Earth radii from the Earth-Sun straight line, and the Earth is also shifting from this line during the solar wind propagation time. IMF parameters may differ between the satellite and the Earth-Sun straight line. In this work, we address a second important problem: solar wind and IMF parameters may change during it's travel from the satellite towards the Earth. It is suggested here that a Magneto-Hydrodynamics approach can be used to deal with this problem. A simplified 1D solar wind propagation model was derived for this case using mass and momentum conservation laws and Maxwell equations. The model is simple and fast enough to use even in real-time applications, yet it takes into account real conservation laws of solar wind motion. To validate this model, comparisons of the IMF data and solar wind parameters were performed for the ACE and WIND satellites. Two different events were used. The first was from April 30, 1999, a day on which both satellites were approximately on the same line with the Sun. In that case
ERIC Educational Resources Information Center
Adney, Kenneth J.
1991-01-01
An activity in which students compare the sun's brightness with that of a light bulb of known luminosity (in watts) to determine the luminosity of the sun is presented. As an extension, the luminosity value that the student obtains for the sun can also be used to estimate the sun's surface temperature. (KR)
Solar tracking control system Sun Chaser
NASA Technical Reports Server (NTRS)
Scott, D. R.; White, P. R.
1978-01-01
The solar tracking control system, Sun Chaser, a method of tracking the Sun in all types of weather conditions is described. The Sun Chaser follows the Sun from east to west in clear or cloudy weather, and resets itself to the east position after sundown in readiness for the next sunrise.
SunShot Initiative Portfolio Book 2014
Solar Energy Technologies Office
2014-05-01
The 2014 SunShot Initiative Portfolio Book outlines the progress towards the goals outlined in the SunShot Vision Study. Contents include overviews of each of SunShot’s five subprogram areas, as well as a description of every active project in the SunShot’s project portfolio as of May 2014.
Pulse Detonation Rocket Magnetohydrodynamic Power Experiment
NASA Technical Reports Server (NTRS)
Litchford, R. J.; Jones, J. E.; Dobson, C. C.; Cole, J. W.; Thompson, B. R.; Plemmons, D. H.; Turner, M. W.
2003-01-01
The production of onboard electrical power by pulse detonation engines is problematic in that they generate no shaft power; however, pulse detonation driven magnetohydrodynamic (MHD) power generation represents one intriguing possibility for attaining self-sustained engine operation and generating large quantities of burst power for onboard electrical systems. To examine this possibility further, a simple heat-sink apparatus was developed for experimentally investigating pulse detonation driven MHD generator concepts. The hydrogen oxygen fired driver was a 90 cm long stainless steel tube having a 4.5 cm square internal cross section and a short Schelkin spiral near the head end to promote rapid formation of a detonation wave. The tube was intermittently filled to atmospheric pressure and seeded with a CsOH/methanol prior to ignition by electrical spark. The driver exhausted through an aluminum nozzle having an area contraction ratio of A*/A(sub zeta) = 1/10 and an area expansion ratio of A(sub zeta)/A* = 3.2 (as limited by available magnet bore size). The nozzle exhausted through a 24-electrode segmented Faraday channel (30.5 cm active length), which was inserted into a 0.6 T permanent magnet assembly. Initial experiments verified proper drive operation with and without the nozzle attachment, and head end pressure and time resolved thrust measurements were acquired. The exhaust jet from the nozzle was interrogated using a polychromatic microwave interferometer yielding an electron number density on the order of 10(exp 12)/cm at the generator entrance. In this case, MHD power generation experiments suffered from severe near-electrode voltage drops and low MHD interaction; i.e., low flow velocity, due to an inherent physical constraint on expansion with the available magnet. Increased scaling, improved seeding techniques, higher magnetic fields, and higher expansion ratios are expected to greatly improve performance.
Numerical Hydrodynamics and Magnetohydrodynamics in General Relativity.
Font, José A
2008-01-01
This article presents a comprehensive overview of numerical hydrodynamics and magneto-hydrodynamics (MHD) in general relativity. Some significant additions have been incorporated with respect to the previous two versions of this review (2000, 2003), most notably the coverage of general-relativistic MHD, a field in which remarkable activity and progress has occurred in the last few years. Correspondingly, the discussion of astrophysical simulations in general-relativistic hydrodynamics is enlarged to account for recent relevant advances, while those dealing with general-relativistic MHD are amply covered in this review for the first time. The basic outline of this article is nevertheless similar to its earlier versions, save for the addition of MHD-related issues throughout. Hence, different formulations of both the hydrodynamics and MHD equations are presented, with special mention of conservative and hyperbolic formulations well adapted to advanced numerical methods. A large sample of numerical approaches for solving such hyperbolic systems of equations is discussed, paying particular attention to solution procedures based on schemes exploiting the characteristic structure of the equations through linearized Riemann solvers. As previously stated, a comprehensive summary of astrophysical simulations in strong gravitational fields is also presented. These are detailed in three basic sections, namely gravitational collapse, black-hole accretion, and neutron-star evolutions; despite the boundaries, these sections may (and in fact do) overlap throughout the discussion. The material contained in these sections highlights the numerical challenges of various representative simulations. It also follows, to some extent, the chronological development of the field, concerning advances in the formulation of the gravitational field, hydrodynamics and MHD equations and the numerical methodology designed to solve them. To keep the length of this article reasonable, an effort has
Global Magnetohydrodynamic Modeling of the Solar Corona
NASA Technical Reports Server (NTRS)
Linker, Jon A.
1998-01-01
The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic fields in the corona, but the line-of-sight component of the global magnetic fields in the photosphere have been routinely measured for many years (for example, at Stanford's Wilcox Solar Observatory, and at the National Solar Observatory at Kitt Peak). The SOI/MDI instrument is now providing high-resolution full-disk magnetograms several times a day. Understanding the large-scale structure of the solar corona and inner heliosphere requires accurately mapping the measured photospheric magnetic field into the corona and outward. Ideally, a model should not only extrapolate the magnetic field, but should self-consistently reconstruct both the plasma and magnetic fields in the corona and solar wind. Support from our NASA SR&T contract has allowed us to develop three-dimensional magnetohydrodynamic (MHD) computations of the solar corona that incorporate observed photospheric magnetic fields into the boundary conditions. These calculations not only describe the magnetic field in the corona and interplanetary spice, but also predict the plasma properties as well. Our computations thus far have been successful in reproducing many aspects of both coronal and interplanetary data, including the structure of the streamer belt, the location of coronal hole boundaries, and the position and shape of the heliospheric current sheet. The most widely used technique for extrapolating the photospheric magnetic field into the corona and heliosphere are potential field models, such as the potential field source-surface model (PFSS),and the potential field current-sheet (PFCS) model
On stability criteria for kinetic magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Ramos, J. J.
2016-12-01
The existence of a potential energy functional in the zero-Larmor-radius collisionless plasma theory of Kruskal & Oberman (Phys. Fluids, vol. 1, 1958 p. 275), Rosenbluth & Rostoker (Phys. Fluids, vol. 2, 1959, p. 23) allows us to derive easily sufficient conditions for linear stability. However, this kinetic magnetohydrodynamics (KMHD) theory does not have a self-adjointness property, making it difficult to derive necessary conditions. In particular, the standard methods to prove that an instability follows if some trial perturbation makes the incremental potential energy negative, which rely on the self-adjointness of the force operator or on the existence of a complete basis of normal modes, are not applicable to KMHD. This paper investigates KMHD linear stability criteria based on the time evolution of initial-value solutions, without recourse to the classic bounds or comparison theorems of Kruskal-Oberman and Rosenbluth-Rostoker for the KMHD potential energy. The adopted approach does not solve the kinetic equations by integration along characteristics and does not require that the particle orbits be periodic or nearly periodic. Most importantly, the investigation of a necessary condition for stability does not require the self-adjointness of the force operator or the existence of a complete basis of normal modes. It is thereby shown that stability in isothermal ideal-MHD is a sufficient condition for stability in KMHD and that, with a proviso on the long-time behaviour of oscillations about stable equilibria, stability in the double-adiabatic fluid theory, including the variation of the parallel fluid displacement, would be a necessary condition for stability in KMHD.
Center for Extended Magnetohydrodynamic Modeling Cooperative Agreement
Carl R. Sovinec
2008-02-15
The Center for Extended Magnetohydrodynamic Modeling (CEMM) is developing computer simulation models for predicting the behavior of magnetically confined plasmas. Over the first phase of support from the Department of Energy’s Scientific Discovery through Advanced Computing (SciDAC) initiative, the focus has been on macroscopic dynamics that alter the confinement properties of magnetic field configurations. The ultimate objective is to provide computational capabilities to predict plasma behavior—not unlike computational weather prediction—to optimize performance and to increase the reliability of magnetic confinement for fusion energy. Numerical modeling aids theoretical research by solving complicated mathematical models of plasma behavior including strong nonlinear effects and the influences of geometrical shaping of actual experiments. The numerical modeling itself remains an area of active research, due to challenges associated with simulating multiple temporal and spatial scales. The research summarized in this report spans computational and physical topics associated with state of the art simulation of magnetized plasmas. The tasks performed for this grant are categorized according to whether they are primarily computational, algorithmic, or application-oriented in nature. All involve the development and use of the Non-Ideal Magnetohydrodynamics with Rotation, Open Discussion (NIMROD) code, which is described at http://nimrodteam.org. With respect to computation, we have tested and refined methods for solving the large algebraic systems of equations that result from our numerical approximations of the physical model. Collaboration with the Terascale Optimal PDE Solvers (TOPS) SciDAC center led us to the SuperLU_DIST software library [http://crd.lbl.gov/~xiaoye/SuperLU/] for solving large sparse matrices using direct methods on parallel computers. Switching to this solver library boosted NIMROD’s performance by a factor of five in typical large
Solar tracking control system Sun Chaser
NASA Technical Reports Server (NTRS)
Scott, D. R.; White, P. R.
1979-01-01
The solar tracking control system (Sun Chaser) is believed to be an improved method of tracking the Sun in all types of weather conditions. The Sun Chaser will follow the Sun from east to west in clear or cloudy weather, and reset itself to the east position after sundown in readiness for the next sunrise. A description of the Sun Chaser hardware and its operation together with results is presented.
Astrophysical processes on the Sun
Parnell, Clare E.
2012-01-01
Over the past two decades, there have been a series of major solar space missions, namely Yohkoh, SOHO, TRACE, and in the past 5 years, STEREO, Hinode and SDO, studying various aspects of the Sun and providing images and spectroscopic data with amazing temporal, spatial and spectral resolution. Over the same period, the type and nature of numerical models in solar physics have been completely revolutionized as a result of widespread accessibility to parallel computers. These unprecedented advances on both observational and theoretical fronts have led to significant improvements in our understanding of many aspects of the Sun's behaviour and furthered our knowledge of plasma physics processes that govern solar and other astrophysical phenomena. In this Theme Issue, the current perspectives on the main astrophysical processes that shape our Sun are reviewed. In this Introduction, they are discussed briefly to help set the scene. PMID:22665891
Magnetohydrodynamics in stationary and axisymmetric spacetimes: A fully covariant approach
Gourgoulhon, Eric; Markakis, Charalampos; Uryu, Koji; Eriguchi, Yoshiharu
2011-05-15
A fully geometrical treatment of general relativistic magnetohydrodynamics is developed under the hypotheses of perfect conductivity, stationarity, and axisymmetry. The spacetime is not assumed to be circular, which allows for greater generality than the Kerr-type spacetimes usually considered in general relativistic magnetohydrodynamics. Expressing the electromagnetic field tensor solely in terms of three scalar fields related to the spacetime symmetries, we generalize previously obtained results in various directions. In particular, we present the first relativistic version of the Soloviev transfield equation, subcases of which lead to fully covariant versions of the Grad-Shafranov equation and of the Stokes equation in the hydrodynamical limit. We have also derived, as another subcase of the relativistic Soloviev equation, the equation governing magnetohydrodynamical equilibria with purely toroidal magnetic fields in stationary and axisymmetric spacetimes.
Magnetohydrodynamic and gasdynamic theories for planetary bow waves
NASA Technical Reports Server (NTRS)
Spreiter, J. R.; Stahara, S. S.
1983-01-01
A bow wave was previously observed in the solar wind upstream of each of the first six planets. The observed properties of these bow waves and the associated plasma flows are outlined, and those features identified that can be described by a continuum magnetohydrodynamic flow theory. An account of the fundamental concepts and current status of the magnetohydrodynamic and gas dynamic theories for solar wind flow past planetary bodies is provided. This includes a critical examination of: (1) the fundamental assumptions of the theories; (2) the various simplifying approximations introduced to obtain tractable mathematical problems; (3) the limitations they impose on the results; and (4) the relationship between the results of the simpler gas dynamic-frozen field theory and the more accurate but less completely worked out magnetohydrodynamic theory. Representative results of the various theories are presented and compared.
SunBlock '99: Young Scientists Investigate the Sun
NASA Astrophysics Data System (ADS)
Walsh, R. W.; Pike, C. D.; Mason, H.; Young, P.; Ireland, J.; Galsgaard, K.
1999-10-01
SunBlock `99 is a Web-based Public Understanding of Science and educational project which seeks to present the very latest solar research as seen through the eyes of young British scientists. These ``solar guides'' discuss not only their scientific interests, but also their extra-curricular activities and the reasons they chose scientific careers; in other words the human face of scientific research. The SunBlock '99 pages gather a range of solar images and movies from current solar space observatories and discuss the underlying physics and its relationship to the school curriculum. The instructional level is pitched at UK secondary school children (aged 13-16 years). It is intended that the material should not only provide a visually appealing introduction to the study of the Sun, but that it should help bridge the often wide gap between classroom science lessons and the research scientist `out in the field'. SunBlock '99 is managed by a team from the Rutherford Appleton Laboratory and the Universities of St Andrews and Cambridge, together with educational consultants. The production has, in part, been sponsored by PPARC and the Millennium Mathematics Project. Web site addresss: http://www.sunblock99.org.uk
NASA Technical Reports Server (NTRS)
Adams, M. L.; Six, N. Frank (Technical Monitor)
2002-01-01
We have in our celestial backyard, a prime example of a variable star. The Sun, long thought to be "perfect" and unvarying, began to reveal its cycles in the early 1600s as Galileo Galilei and Christoph Scheiner used a telescope to study sunspots. For the past four hundred years, scientists have accumulated data, showing a magnetic cycle that repeats, on average, every eleven (or twenty-two) years. In addition, modern satellites have shown that the energy output at radio and x-ray wavelengths also varies with this cycle. This talk will showcase the Sun as a star and discuss how solar studies may be used to understand other stars.
NASA Technical Reports Server (NTRS)
Whitmire, D. P.; Doyle, L. R.; Reynolds, R. T.; Whitman, P. G.
1993-01-01
Global mean temperatures near 273 K on early Mars are difficult to explain in the context of standards solar evolution models. Even assuming maximum CO2 greenhouse warming, the required flux is approximately 15 percent too low. Here we consider two astrophysical models that could increase the flux by this amount. The first model is a nonstandard solar model in which the early Sun had a mass somewhat greater than today's mass (1.02-1.06 solar mass). The second model is based on a standard evolutionary solar model, but the ecliptic flux is increased due to focusing by an (expected) heavily spotted early Sun.
NICIL: Non-Ideal magnetohydrodynamics Coefficients and Ionisation Library
NASA Astrophysics Data System (ADS)
Wurster, James
2016-08-01
NICIL (Non-Ideal magnetohydrodynamics Coefficients and Ionisation Library) calculates the ionization values and the coefficients of the non-ideal magnetohydrodynamics terms of Ohmic resistivity, the Hall effect, and ambipolar diffusion. Written as a standalone Fortran90 module that can be implemented in existing codes, NICIL is fully parameterizable, allowing the user to choose which processes to include and decide the values of the free parameters. The module includes both cosmic ray and thermal ionization; the former includes two ion species and three species of dust grains (positively charged, negatively charged and neutral), and the latter includes five elements which can be doubly ionized.
Sun protection and skin self-examination in melanoma survivors
Mujumdar, Urvi J.; Hay, Jennifer L.; Monroe-Hinds, Yvette C.; Hummer, Amanda J.; Begg, Colin B.; Wilcox, Homer B.; Oliveria, Susan A.; Berwick, Marianne
2009-01-01
Patients diagnosed with melanoma are at risk for developing recurrent and second primary disease. Skin self-examination (SSE) and sun protection are standard clinical recommendations to minimize risk. In this study we examined performance of these behaviors in individuals with melanoma drawn from the general population. Potential participants (N=148) with a first primary melanoma diagnosed in 2000 were identified through a population-based cancer registry in New Jersey, USA. One hundred and fifteen individuals participated in a 30-minute telephone interview concerning behavioral adherence with SSE and sun protection, self-efficacy for performing these behaviors, and perceived risk of developing another skin cancer. We utilized logistic regression to estimate potential associations of demographic, medical, and psychosocial factors with SSE and sun protection, respectively. Seventeen percent of subjects reported performing comprehensive SSE at least once every two months and 23% engaged in regular sun protection. Utilization of SSE was related to the presence of moles (OR= 4.2, 95% CI: 1.1-15) and higher SSE self-efficacy (OR= 14.4, 95% CI: 1.9-112). Regular sun protection was related to older age (>60 years; OR= 3.3, 95% CI: 1.3-8.7), being female (OR= 2.8, 95% CI: 1.1-7.3) and higher sun protection self-efficacy (OR= 5.0, 95% CI: 1.4-18). These factors remained significant in multivariate models. In this group of primary melanoma survivors, the rates of SSE and sun protection are comparable to, but do not exceed, general population estimates. This study provides justification for further research to address barriers to prevention and control behaviors in melanoma survivors. PMID:19142859
A magnetohydrodynamic theory of coronal loop transients
NASA Technical Reports Server (NTRS)
Yeh, T.
1982-01-01
The physical and geometrical characteristics of solar coronal loop transients are described in an MHD model based on Archimedes' MHD buoyancy force. The theory was developed from interpretation of coronagraphic data, particularly from Skylab. The brightness of a loop is taken to indicate the electron density, and successive pictures reveal the electron enhancement in different columns. The forces which lift the loop off the sun surface are analyzed as an MHD buoyancy force affecting every mass element by imparting an inertial force necessary for heliocentrifugal motion. Thermal forces are responsible for transferring the ambient stress to the interior of the loop to begin the process. The kinematic and hydrostatic buoyancy overcome the gravitational force, and a flux rope can then curve upward, spiralling like a corkscrew with varying cross section around the unwinding solar magnetic field lines.
Perturbing macroscopic magnetohydrodynamic stability for toroidal plasmas
NASA Astrophysics Data System (ADS)
Comer, Kathryn J.
We have introduced a new perturbative technique to rapidly explore the dependence of long wavelength ideal magnetohydrodynamic (MHD) instabilities on equilibrium profiles, shaping properties, and wall parameters. Traditionally, these relations are studied with numerical parameter scans using computationally intensive stability codes. Our perturbative technique first finds the equilibrium and stability using traditional methods. Subsequent small changes in the original equilibrium parameters change the stability. We quickly find the new stability with an expansion of the energy principle, rather than with another run of the stability codes. We first semi-analytically apply the technique to the screw pinch after eliminating compressional Alfven wave effects. The screw pinch results validate the approach, but also indicate that allowable perturbations to equilibria with certain features may be restricted. Next, we extend the approach to toroidal geometry using experimental equilibria and a simple constructed equilibrium, with the ideal MHD stability code GATO. Stability properties are successfully predicted from perturbed toroidal equilibria when only the vacuum beyond the plasma is perturbed (through wall parameter variations), rather than the plasma itself. Small plasma equilibrium perturbations to both experimental and simple equilibria result in very large errors to the predicted stability, and valid results are found only over a narrow range of most perturbations. Despite the large errors produced when changing plasma parameters, the wall perturbations revealed two useful applications of this technique. Because the calculations are non-iterative matrix multiplications, the convergence issues that can disrupt a full MHD stability code are absent. Marginal stability, therefore, is much easier to find with the perturbative technique. Also, the perturbed results can be input as the initial guess for the eigenvalue for a full stability code, and improve subsequent
Magnetic control of magnetohydrodynamic instabilities in tokamaks
NASA Astrophysics Data System (ADS)
Strait, E. J.
2015-02-01
Externally applied, non-axisymmetric magnetic fields form the basis of several relatively simple and direct methods to control magnetohydrodynamic (MHD) instabilities in a tokamak, and most present and planned tokamaks now include a set of non-axisymmetric control coils for application of fields with low toroidal mode numbers. Non-axisymmetric applied fields are routinely used to compensate small asymmetries ( δB /B ˜10-3 to 10-4 ) of the nominally axisymmetric field, which otherwise can lead to instabilities through braking of plasma rotation and through direct stimulus of tearing modes or kink modes. This compensation may be feedback-controlled, based on the magnetic response of the plasma to the external fields. Non-axisymmetric fields are used for direct magnetic stabilization of the resistive wall mode—a kink instability with a growth rate slow enough that feedback control is practical. Saturated magnetic islands are also manipulated directly with non-axisymmetric fields, in order to unlock them from the wall and spin them to aid stabilization, or position them for suppression by localized current drive. Several recent scientific advances form the foundation of these developments in the control of instabilities. Most fundamental is the understanding that stable kink modes play a crucial role in the coupling of non-axisymmetric fields to the plasma, determining which field configurations couple most strongly, how the coupling depends on plasma conditions, and whether external asymmetries are amplified by the plasma. A major advance for the physics of high-beta plasmas ( β = plasma pressure/magnetic field pressure) has been the understanding that drift-kinetic resonances can stabilize the resistive wall mode at pressures well above the ideal-MHD stability limit, but also that such discharges can be very sensitive to external asymmetries. The common physics of stable kink modes has brought significant unification to the topics of static error fields at low
Magnetic control of magnetohydrodynamic instabilities in tokamaks
Strait, E. J.
2015-02-15
Externally applied, non-axisymmetric magnetic fields form the basis of several relatively simple and direct methods to control magnetohydrodynamic (MHD) instabilities in a tokamak, and most present and planned tokamaks now include a set of non-axisymmetric control coils for application of fields with low toroidal mode numbers. Non-axisymmetric applied fields are routinely used to compensate small asymmetries (δB/B∼10{sup −3} to 10{sup −4}) of the nominally axisymmetric field, which otherwise can lead to instabilities through braking of plasma rotation and through direct stimulus of tearing modes or kink modes. This compensation may be feedback-controlled, based on the magnetic response of the plasma to the external fields. Non-axisymmetric fields are used for direct magnetic stabilization of the resistive wall mode—a kink instability with a growth rate slow enough that feedback control is practical. Saturated magnetic islands are also manipulated directly with non-axisymmetric fields, in order to unlock them from the wall and spin them to aid stabilization, or position them for suppression by localized current drive. Several recent scientific advances form the foundation of these developments in the control of instabilities. Most fundamental is the understanding that stable kink modes play a crucial role in the coupling of non-axisymmetric fields to the plasma, determining which field configurations couple most strongly, how the coupling depends on plasma conditions, and whether external asymmetries are amplified by the plasma. A major advance for the physics of high-beta plasmas (β = plasma pressure/magnetic field pressure) has been the understanding that drift-kinetic resonances can stabilize the resistive wall mode at pressures well above the ideal-MHD stability limit, but also that such discharges can be very sensitive to external asymmetries. The common physics of stable kink modes has brought significant unification to the topics of static error
Integrated Pulse Detonation Propulsion and Magnetohydrodynamic Power
NASA Technical Reports Server (NTRS)
Litchford, R. J.; Lyles, Garry M. (Technical Monitor)
2001-01-01
The prospects for realizing an integrated pulse detonation propulsion and magnetohydrodynamic (MHD) power system are examined. First, energy requirements for direct detonation initiation of various fuel-oxygen and fuel-air mixtures are deduced from available experimental data and theoretical models. Second, the pumping power requirements for effective chamber scavenging are examined through the introduction of a scavenging ratio parameter and a scavenging efficiency parameter. A series of laboratory experiments were carried out to investigate the basic engineering performance characteristics of a pulse detonation-driven MHD electric power generator. In these experiments, stoichiometric oxy-acetylene mixtures seeded with a cesium hydroxide/methanol spray were detonated at atmospheric pressure in a 1-m-long tube having an i.d. of 2.54 cm. Experiments with a plasma diagnostic channel attached to the end of the tube confirmed the attainment of detonation conditions (p(sub 2)/p(sub 1) approx. 34 and D approx. 2,400 m/sec) and enabled the direct measurement of current density and electrical conductivity (=6 S/m) behind the detonation wave front. In a second set of experiments, a 30-cm-long continuous electrode Faraday channel, having a height of 2.54 cm and a width of 2 cm, was attached to the end of the tube using an area transition duct. The Faraday channel was inserted in applied magnetic fields of 0.6 and 0.95 T. and the electrodes were connected to an active loading circuit to characterize power extraction dependence on load impedance while also simulating higher effective magnetic induction. The experiments indicated peak power extraction at a load impedance between 5 and 10 Ohm. The measured power density was in reasonable agreement with a simple electrodynamic model incorporating a correction for near-electrode potential losses. The time-resolved thrust characteristics of the system were also measured, and it was found that the MHD interaction exerted a
Integrated Pulse Detonation Propulsion and Magnetohydrodynamic Power
NASA Technical Reports Server (NTRS)
Litchford, Ron J.
2001-01-01
The prospects for realizing an integrated pulse detonation propulsion and magnetohydrodynamic (MHD) power system are examined. First, energy requirements for direct detonation initiation of various fuel-oxygen and fuel-air mixtures are deduced from available experimental data and theoretical models. Second, the pumping power requirements for effective chamber scavenging are examined through the introduction of a scavenging ratio parameter and a scavenging efficiency parameter. A series of laboratory experiments were carried out to investigate the basic engineering performance characteristics of a pulse detonation-driven MHD electric power generator. In these experiments, stoichiometric oxy-acetylene mixtures seeded with a cesium hydroxide/methanol spray were detonated at atmospheric pressure in a 1-m-long tube having an i.d. of 2.54 cm. Experiments with a plasma diagnostic channel attached to the end of the tube confirmed the attainment of detonation conditions (p2/p1 approximately 34 and D approximately 2,400 m/sec) and enabled the direct measurement of current density and electrical conductivity (approximately = 6 S/m) behind the detonation wave front, In a second set of experiments, a 30-cm-long continuous electrode Faraday channel, having a height of 2.54 cm and a width of 2 cm, was attached to the end of the tube using an area transition duct. The Faraday channel was inserted in applied magnetic fields of 0.6 and 0.95 T, and the electrodes were connected to an active loading circuit to characterize power extraction dependence on load impedance while also simulating higher effective magnetic induction. The experiments indicated peak power extraction at a load impedance between 5 and 10 Omega. The measured power density was in reasonable agreement with a simple electrodynamic model incorporating a correction for near-electrode potential losses. The time-resolved thrust characteristics of the system were also measured, and it was found that the NM interaction
Project SUN (Students Understanding Nature)
NASA Technical Reports Server (NTRS)
Curley, T.; Yanow, G.
1995-01-01
Project SUN is part of NASA's 'Mission to Planet Earth' education outreach effort. It is based on development of low cost, scientifi- cally accurate instrumentation and computer interfacing, coupled with Apple II computers as dedicated data loggers. The project is com- prised of: instruments, interfacing, software, curriculum, a detailed operating manual, and a system of training at the school sites.
Protecting Yourself from Sun Exposure
... prolonged exposure to the sun when possible. ■■ Wear sunscreen with a minimum of SPF 15. ӽӽ SPF ... 1789, titanium dioxide, zinc oxide, or avobenzone. ӽӽ Sunscreen performance is affected by wind, humidity, perspiration, and ...
Tracking Planets around the Sun
ERIC Educational Resources Information Center
Riddle, Bob
2008-01-01
In earlier columns, the celestial coordinate system of hour circles of right ascension and degrees of declination was introduced along with the use of an equatorial star chart (see SFA Star Charts in Resources). This system shows the planets' motion relative to the ecliptic, the apparent path the Sun follows during the year. An alternate system,…
Seismology and the Wounded Sun
NASA Astrophysics Data System (ADS)
Cally, Paul
2016-05-01
Active regions provide an opening in the Sun's surface that allow seismic waves to penetrate the overlying atmosphere. Some proportion then return due to reflection, with implications for "internal" seismology. This is illustrated using simulations with particular reference to "travel times" and acoustic halos.
ERIC Educational Resources Information Center
Giles-Corti, B.; English, D. R.; Costa, C.; Milne, E.; Cross, D.; Johnston, R.
2004-01-01
Kidskin was a sun-protection intervention study involving 1776 children attending 33 primary schools in Perth, Western Australia. There were three study groups: a control group, a moderate intervention group and a high intervention group. In addition to receiving a specially designed curricular intervention (1995-1998), the moderate and high…
The Sun's Crowded Delivery Room
NASA Astrophysics Data System (ADS)
Taylor, G. J.
2007-07-01
Astronomic observations with the latest and greatest telescopes are leading astronomers to embrace the idea that stars usually form in clusters, even if they end up, like our Sun, isolated from other stars. Cosmochemists using optical microscopes, electron microscopes, and mass spectrometers are finding evidence supporting the idea, along with important details about the star-forming regions and about the earliest history of the Solar System. The latest breakthrough is reported by Martin Bizzarro and his colleagues at the Geological Institute and Geological Museum in Denmark, at the University of Texas, and at Clemson University in South Carolina. They made high-precision measurements of iron and nickel isotopes. The results show that the oldest planetesimals to form in the solar system did not contain any iron-60, which decays to nickel-60 with a half-life of only 1.5 million years, yet somewhat younger materials did contain it. In contrast, aluminum-26, with a half-life of 740,000 years, was relatively uniformly distributed. This suggests to Bizzarro and his colleagues that iron-60 was added to the cloud of gas and dust surrounding the primitive Sun (the protoplanetary disk) about 1 million years after the Solar System formed. This could happen if the Sun's nursery contained massive stars (perhaps 30 times the mass of the Sun). Such stars last only about 4 million years. They are extremely active, blowing away their outer layers in the last million years of existence. The dispersed material would have included aluminum-26 and might have caused collapse of interstellar gas and dust to cause formation of the Sun and its protoplanetary disk. A million years later the massive star exploded, ejecting iron-60 from its interior. Bizzarro and colleagues argue that this huge event of destruction and creation is recorded in the meteorites.
Decay rates of the magnetohydrodynamic model for quantum plasmas
NASA Astrophysics Data System (ADS)
Pu, Xueke; Xu, Xiuli
2017-02-01
In this paper, we consider the quantum magnetohydrodynamic model for quantum plasmas. We prove the optimal decay rates for the solution to the constant state in the whole space in the Lp-norm with 2≤ p≤ 6 and its first derivatives in L2-norm. The proof is based on the optimal decay of the linearized equation and nonlinear energy estimates.
A stochastic approach to the solution of magnetohydrodynamic equations
Floriani, E.; Vilela Mendes, R.
2013-06-01
The construction of stochastic solutions is a powerful method to obtain localized solutions in configuration or Fourier space and for parallel computation with domain decomposition. Here a stochastic solution is obtained for the magnetohydrodynamics equations. Some details are given concerning the numerical implementation of the solution which is illustrated by an example of generation of long-range magnetic fields by a velocity source.
Instability of the magnetohydrodynamics system at vanishing Reynolds number
NASA Astrophysics Data System (ADS)
Bouya, Ismaël
2013-12-01
The aim of this note is to study the dynamo properties of the magnetohydrodynamics system at vanishing R m . Improving the analysis in Gérard-Varet (SIAM J Math Anal 37(3):815-840, 2006), we shall establish a generic Lyapunov instability result.
Has the Sun Significantly Impacted Recent Voyager Observations?
NASA Astrophysics Data System (ADS)
Intriligator, D. S.; Sun, W.; Detman, T. R.; Dryer, Ph. D., M.; Deehr, C. S.; Intriligator, J.; Webber, W. R.
2013-12-01
Using our models HAFSS (HAF Source Surface) and HHMS-PI (Hybrid Heliospheric Modeling System with Pickup Protons) we have been analyzing some of the recent (e.g., July 2012, etc.) solar events to determine if the effects of the events might be seen in the outer heliosphere, heliosheath, etc. Our analyses provide insights into the phenomena in these regions. Both models are three-dimensional (3D) time dependent simulations that use solar observations as input. HAFSS is a kinematic model. HHMS-PI is a numerical magnetohydrodynamic solar wind (SW) simulation model. Both HHMS-PI and HAFSS are ideally suited for these analyses since starting from the Sun they model the slowly evolving background SW and the impulsive, time-dependent events associated with solar activity (e.g., coronal mass ejections (CMEs). HHMS-PI/HAFSS make it possible to track interplanetary shocks as they propagate, interact, and evolve en route to various spacecraft (s/c) where they are observed. Our models have been used to reproduce s/c data from ACE to Ulysses, Cassini, and Voyagers 1 and 2. Our published results in refereed scientific journals showed that: a.) Our models naturally reproduce dynamic 3D spatially asymmetric effects observed throughout the heliosphere. b.) Pre-existing SW background conditions have a strong influence on the propagation of shock waves from solar events. c.) Time-dependence is a crucial aspect of interpreting s/c data. d.) Shock interactions resulting from multiple solar events lead to complicated time-series observations at individual s/c. We believe the answer to the question in the title of this abstract is: Yes, we do think the Sun has significantly impacted recent Voyager observations.
NASA Technical Reports Server (NTRS)
2004-01-01
On Sol 20 of its journey, Mars Exploration Rover Opportunity woke up around 5:30 in the martian afternoon to watch the sunset. A series of five sets of three-color images from the rover's panoramic camera was acquired looking toward the southwest. Each set used an infrared, green and violet filter, rather than the human red-green-blue, so that the maximum panoramic camera wavelength range could be covered by the observations, enhancing the scientific value of the measurements.
A color image was made from the first post-sunset sequence of calibrated color images, with the color balance set to approximate what the sunset color would have looked like to the human eye. The color seen in this first post-sunset image was then used to colorize each image in the sequence. Approximately one-minute gaps between consecutive color images meant the Sun's position changed within each color set, so the images had to be manually shifted to compensate for this motion. In this fashion, the position and brightness of the Sun are taken from each individual image, but the color is taken from a single set of images. The images were then combined into a movie where one color set fades gracefully into the next. Analysis of the five color sets shows that there were only small color variations during the sunset, so most of the real variations are captured in the movie.
The rapid dimming of the Sun near the horizon is due to the dust in the sky. There is nearly twice as much dust as there was when the Mars Pathfinder spacecraft, which landed on Mars in 1997, imaged the sunset. This causes the Sun to be many times fainter. The sky above the Sun has the same blue tint observed by Pathfinder and also by Viking, which landed on Mars in 1976. This is because dust in the martian atmosphere scatters blue light forward toward the observer much more efficiently than it scatters red light forward. Therefore, a 'halo' of blueish sky color is always observed close to the Sun. We're only seeing
GOES Weather Satellite Watches The Sun
NASA satellites such as STEREO, SOHO, and SDO are dedicated to studying the sun. GOES is a weather satellite but also watches the sun constantly. Watch this video and learn why space weather data i...
SDO Watches Giant Filament on the Sun
A snaking, extended filament of solar material currently lies on the front of the sun-- some 1 million miles across from end to end. Filaments are clouds of solar material suspended above the sun b...
Essential Outdoor Sun Safety Tips for Winter
... the risk for damage. Both snow and strong wind can wear away sunscreen and reduce its effectiveness, ... protect your skin from the bitter cold, heavy winds and winter sun, follow these important sun protection ...
Our prodigal sun. [solar energy technology
NASA Technical Reports Server (NTRS)
1974-01-01
Characteristics of the sun are reported indicating it as a source of energy. Data from several space missions are discussed, and the solar activity cycle is presented. The corona, flares, prominences, spots, and wind of the sun are also discussed.
Our World: The Sun, A Real Star
Learn about the important relationship between Earth and the sun. Find out about the layers of the sun and how Earth's magnetosphere acts like a giant handkerchief to protect us from all kinds of s...
BOOK REVIEW: Magnetohydrodynamics of Plasma Relaxation
NASA Astrophysics Data System (ADS)
Connor, J. W.
1998-06-01
This monograph on magnetohydrodynamic (MHD) relaxation in plasmas by Ortolani and Schnack occupies a fascinating niche in the plasma physics literature. It is rare in the complex and often technically sophisticated subject of plasma physics to be able to isolate a topic and deal with it comprehensively in a mere 180 pages. Furthermore, it brings a refreshingly original and personal approach to the treatment of plasma relaxation, synthesizing the experiences of the two authors to produce a very readable account of phenomena appearing in such diverse situations as laboratory reversed field pinches (RFPs) and the solar corona. Its novelty lies in that, while it does acknowledge the seminal Taylor theory of relaxation as a general guide, it emphasizes the role of large scale numerical MHD simulations in developing a picture for the relaxation phenomena observed in experiment and nature. Nevertheless, the volume has some minor shortcomings: a tendency to repetitiveness and some omissions that prevent it being entirely self-contained. The monograph is divided into nine chapters, with the first a readable, `chatty', introduction to the physics and phenomena of relaxation discussed in the later chapters. Chapter 2 develops the tools for describing relaxation processes, namely the resistive MHD model, leading to a discussion of resistive instabilities and the stability properties of RFPs. This chapter demonstrates the authors' confessed desire to avoid mathematical detail with a rather simplified discussion of Δ' and magnetic islands; it also sets the stage for their own belief, or thesis, that numerical simulation of the non-linear consequences of the MHD model is the best approach to explaining the physics of relaxation. Nevertheless, in Chapter 3 they provide a reasonably good account and critique of one analytic approach that is available, and which is the commonly accepted picture for relaxation in pinches - the Taylor relaxation theory based on the conservation of
Caddo Sun Accounts across Time and Place
ERIC Educational Resources Information Center
Gerona, Carla
2012-01-01
Billy Day, a Tunica/Biloxi, recently described the significance of the sun for Caddoan people. Day quoted an "old Caddo relative" of his who said: "I used to go outside and hold my hands up and bless myself with the sun--'a'hat.' Well, I can't do that anymore because they say we are sun worshipers. We didn't worship the sun. We worshiped what was…
Bayesian seismology of the Sun
NASA Astrophysics Data System (ADS)
Gruberbauer, M.; Guenther, D. B.
2013-06-01
We perform a Bayesian grid-based analysis of the solar l = 0, 1, 2 and 3 p modes obtained via BiSON in order to deliver the first Bayesian asteroseismic analysis of the solar composition problem. We do not find decisive evidence to prefer either of the contending chemical compositions, although the revised solar abundances (AGSS09) are more probable in general. We do find indications for systematic problems in standard stellar evolution models, unrelated to the consequences of inadequate modelling of the outer layers on the higher order modes. The seismic observables are best fitted by solar models that are several hundred million years older than the meteoritic age of the Sun. Similarly, meteoritic age calibrated models do not adequately reproduce the observed seismic observables. Our results suggest that these problems will affect any asteroseismic inference that relies on a calibration to the Sun.
NASA Astrophysics Data System (ADS)
Cheng, Andrew F.
The Sun's action on the Earth is fundamentally responsible for maintaining the physical conditions that support life on the land, in the oceans, and in the atmosphere, and a comprehensive understanding of this action should be a central concern of scientific endeavor. The Sun's influence goes beyond providing energy to the biosphere and maintaining the Earth's climate and weather; it strongly affects the Earth's upper atmosphere and ionosphere as well as the magnetosphere, the region of space permeated by the terrestrial magnetic field and occupied by ionized gases. Flares and other solar disturbances can produce strong reactions in the Earth's ionosphere, magnetic field, and space plasma environment, often within 20 minutes of onset. As human activity extends into space, and to the Moon and planets, scientific understanding of solar-terrestrial interactions and, more generally, of the space environment's physics will assume increasing importance.
Zirker, J B
1980-12-19
Total eclipses of the sun offer research opportunities in a variety of sciences. Some of the advances in solar physics resulting from eclipse observations are discussed. Experiments at the total eclipse of 16 February 1980 in India are also described. These included a test of general relativity, studies in coronal physics, investigations of solar prominences, diameter measurements, a search for interplanetary dust, a study of the gravity waves in the earth's atmosphere, and experiments on the biological effects on animals and humans.
NASA Astrophysics Data System (ADS)
Bokhove, H.
The High Accuracy Sun Sensor (HASS) is described, concentrating on measurement principle, the CCD detector used, the construction of the sensorhead and the operation of the sensor electronics. Tests on a development model show that the main aim of a 0.01-arcsec rms stability over a 10-minute period is closely approached. Remaining problem areas are associated with the sensor sensitivity to illumination level variations, the shielding of the detector, and the test and calibration equipment.
Sun and Other Types of Radiation
... Español Category Cancer A-Z What Causes Cancer? Sun and Other Types of Radiation Learn about the different types of radiation and how exposure might affect cancer risk. UV Radiation (Sun) Ultraviolet (UV) radiation comes from the sun and ...
SunWise[R] Meteorologist Tool Kit
ERIC Educational Resources Information Center
US Environmental Protection Agency, 2007
2007-01-01
The SunWise Program is designed to help meteorologists raise sun safety awareness by addressing the science of the sun, the risk of overexposure to its ultraviolet (UV) radiation, and what students and their families can do to protect themselves from overexposure. This Tool Kit has been designed for use all over the United States and its…
Encouraging Sun Safety for Children and Adolescents
ERIC Educational Resources Information Center
Boe, Kathy; Tillotson, Elizabeth A.
2006-01-01
The rise in the number of cases of skin cancers, both melanomas and nonmelanomas, has prompted increased awareness and educational efforts to limit sun exposure. Because 80% of lifetime sun exposure occurs before the age of 18, educating parents and adolescents to incorporate sun-protective behaviors into daily routines is particularly important.…
Sun Tracker Operates a Year Between Calibrations
NASA Technical Reports Server (NTRS)
Berdahl, C. M.
1984-01-01
Low-cost modification of Sun tracker automatically compensates equation of time and seasonal variations in declination of Sun. Output of Scotch Yoke drive mechanism adjusted through proper sizing of crank, yoke and other components and through choice of gear ratios to approximate seasonal northand south motion of Sun. Used for industrial solar-energy monitoring and in remote meteorological stations.
Sun tracker for clear or cloudy weather
NASA Technical Reports Server (NTRS)
Scott, D. R.; White, P. R.
1979-01-01
Sun tracker orients solar collector so that they absorb maximum possible sunlight without being fooled by bright clouds, holes in cloud cover, or other atmospheric conditions. Tracker follows sun within 0.25 deg arc and is accurate within + or - 5 deg when sun is hidden.
NASA Astrophysics Data System (ADS)
Martens, Petrus C.; White, Russel J.
2016-05-01
The Sun represents only one realization of the many possibilities for stellar dynamos. In order to fully understand the physics of solar and stellar magnetism we need to study in full detail the magnetic cycles of stars that are very much like the Sun . To do this we need a telescope that can resolve the disks of nearby solar type stars. Georgia State's University Center for High Resolution Astronomy (CHARA) array is a diffraction limited interferometer with a baseline of over 300 m, located on Mount Wilson. It is the highest resolution telescope in the visible and infrared currently in operation. CHARA has resolved the disks of larger stars and observed starspots. We will describe an ongoing observing program for nearby Sun-like stars to determine with great accuracy the basic parameters of these stars and the presence of starspots on their surfaces. Combined with the decades long observations of Mount Wilson and Lowell Observatories of stellar cycles the data obtained will act as a powerful constraint on solar and stellar dynamo models and simulations.
Micro Sun Sensor for Spacecraft
NASA Technical Reports Server (NTRS)
Mobasser, Sohrab; Liebe, Carl; Bae, Youngsam; Schroeder, Jeffrey; Wrigley, Chris
2004-01-01
A report describes the development of a compact micro Sun sensor for use as a part of the attitude determination subsystem aboard future miniature spacecraft and planetary robotic vehicles. The prototype unit has a mass of only 9 g, a volume of only 4.2 cm(sup 3), a power consumption of only 30 mW, and a 120 degree field of view. The unit has demonstrated an accuracy of 1 arcminute. The unit consists of a multiple pinhole camera: A micromachined mask containing a rectangular array of microscopic pinholes, machined utilizing the microectromechanical systems (MEMS), is mounted in front of an active-pixel sensor (APS) image detector. The APS consists of a 512 x 512-pixel array, on-chip 10-bit analog to digital converter (ADC), on-chip bias generation, and on-chip timing control for self-sequencing and easy programmability. The digitized output of the APS is processed to compute the centroids of the pinhole Sun images on the APS. The Sun angle, relative to a coordinate system fixed to the sensor unit, is then computed from the positions of the centroids.
NASA Technical Reports Server (NTRS)
Usmanov, Arcadi V.; Goldstein, Melvyn L.; Matthaeus, William H.
2012-01-01
To study the effects of interstellar pickup protons and turbulence on the structure and dynamics of the solar wind, we have developed a fully three-dimensional magnetohydrodynamic solar wind model that treats interstellar pickup protons as a separate fluid and incorporates the transport of turbulence and turbulent heating. The governing system of equations combines the mean-field equations for the solar wind plasma, magnetic field, and pickup protons and the turbulence transport equations for the turbulent energy, normalized cross-helicity, and correlation length. The model equations account for photoionization of interstellar hydrogen atoms and their charge exchange with solar wind protons, energy transfer from pickup protons to solar wind protons, and plasma heating by turbulent dissipation. Separate mass and energy equations are used for the solar wind and pickup protons, though a single momentum equation is employed under the assumption that the pickup protons are comoving with the solar wind protons.We compute the global structure of the solar wind plasma, magnetic field, and turbulence in the region from 0.3 to 100 AU for a source magnetic dipole on the Sun tilted by 0 deg - .90 deg and compare our results with Voyager 2 observations. The results computed with and without pickup protons are superposed to evaluate quantitatively the deceleration and heating effects of pickup protons, the overall compression of the magnetic field in the outer heliosphere caused by deceleration, and the weakening of corotating interaction regions by the thermal pressure of pickup protons.
Reconnection-driven Magnetohydrodynamic Turbulence in a Simulated Coronal-hole Jet
NASA Astrophysics Data System (ADS)
Uritsky, Vadim M.; Roberts, Merrill A.; DeVore, C. Richard; Karpen, Judith T.
2017-03-01
Extreme-ultraviolet and X-ray jets occur frequently in magnetically open coronal holes on the Sun, especially at high solar latitudes. Some of these jets are observed by white-light coronagraphs as they propagate through the outer corona toward the inner heliosphere, and it has been proposed that they give rise to microstreams and torsional Alfvén waves detected in situ in the solar wind. To predict and understand the signatures of coronal-hole jets, we have performed a detailed statistical analysis of such a jet simulated by an adaptively refined magnetohydrodynamics model. The results confirm the generation and persistence of three-dimensional, reconnection-driven magnetic turbulence in the simulation. We calculate the spatial correlations of magnetic fluctuations within the jet and find that they agree best with the Müller–Biskamp scaling model including intermittent current sheets of various sizes coupled via hydrodynamic turbulent cascade. The anisotropy of the magnetic fluctuations and the spatial orientation of the current sheets are consistent with an ensemble of nonlinear Alfvén waves. These properties also reflect the overall collimated jet structure imposed by the geometry of the reconnecting magnetic field. A comparison with Ulysses observations shows that turbulence in the jet wake is in quantitative agreement with that in the fast solar wind.
Data-constrained Coronal Mass Ejections in a Global Magnetohydrodynamics Model
NASA Astrophysics Data System (ADS)
Jin, M.; Manchester, W. B.; van der Holst, B.; Sokolov, I.; Tóth, G.; Mullinix, R. E.; Taktakishvili, A.; Chulaki, A.; Gombosi, T. I.
2017-01-01
We present a first-principles-based coronal mass ejection (CME) model suitable for both scientific and operational purposes by combining a global magnetohydrodynamics (MHD) solar wind model with a flux-rope-driven CME model. Realistic CME events are simulated self-consistently with high fidelity and forecasting capability by constraining initial flux rope parameters with observational data from GONG, SOHO/LASCO, and STEREO/COR. We automate this process so that minimum manual intervention is required in specifying the CME initial state. With the newly developed data-driven Eruptive Event Generator using Gibson–Low configuration, we present a method to derive Gibson–Low flux rope parameters through a handful of observational quantities so that the modeled CMEs can propagate with the desired CME speeds near the Sun. A test result with CMEs launched with different Carrington rotation magnetograms is shown. Our study shows a promising result for using the first-principles-based MHD global model as a forecasting tool, which is capable of predicting the CME direction of propagation, arrival time, and ICME magnetic field at 1 au (see the companion paper by Jin et al. 2016a).
THE HANLE EFFECT OF Ly{alpha} IN A MAGNETOHYDRODYNAMIC MODEL OF THE SOLAR TRANSITION REGION
Stepan, J.; Trujillo Bueno, J.; Carlsson, M.; Leenaarts, J.
2012-10-20
In order to understand the heating of the solar corona it is crucial to obtain empirical information on the magnetic field in its lower boundary (the transition region). To this end, we need to measure and model the linear polarization produced by scattering processes in strong UV lines, such as the hydrogen Ly{alpha} line. The interpretation of the observed Stokes profiles will require taking into account that the outer solar atmosphere is highly structured and dynamic, and that the height of the transition region may well vary from one place in the atmosphere to another. Here, we report on the Ly{alpha} scattering polarization signals we have calculated in a realistic model of an enhanced network region, resulting from a state-of-the-art radiation magnetohydrodynamic simulation. This model is characterized by spatially complex variations of the physical quantities at transition region heights. The results of our investigation lead us to emphasize that scattering processes in the upper solar chromosphere should indeed produce measurable linear polarization in Ly{alpha}. More importantly, we show that via the Hanle effect the model's magnetic field produces significant changes in the emergent Q/I and U/I profiles. Therefore, we argue that by measuring the polarization signals produced by scattering processes and the Hanle effect in Ly{alpha} and contrasting them with those computed in increasingly realistic atmospheric models, we should be able to decipher the magnetic, thermal, and dynamic structure of the upper chromosphere and transition region of the Sun.
Magnetohydrodynamics with Embedded Particle-in-Cell Simulation of Mercury's Magnetosphere
NASA Astrophysics Data System (ADS)
Chen, Y.; Toth, G.; Jia, X.; Gombosi, T. I.; Markidis, S.
2015-12-01
Mercury's magnetosphere is much more dynamic than other planetary magnetospheres because of Mercury's weak intrinsic magnetic field and its proximity to the Sun. Magnetic reconnection and Kelvin-Helmholtz phenomena occur in Mercury's magnetopause and magnetotail at higher frequencies than in other planetary magnetosphere. For instance, chains of flux transfer events (FTEs) on the magnetopause, have been frequentlyobserved by the the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft (Slavin et al., 2012). Because ion Larmor radius is comparable to typical spatial scales in Mercury's magnetosphere, finite Larmor radius effects need to be accounted for. In addition, it is important to take in account non-ideal dissipation mechanisms to accurately describe magnetic reconnection. A kinetic approach allows us to model these phenomena accurately. However, kinetic global simulations, even for small-size magnetospheres like Mercury's, are currently unfeasible because of the high computational cost. In this work, we carry out global simulations of Mercury's magnetosphere with the recently developed MHD-EPIC model, which is a two-way coupling of the extended magnetohydrodynamic (XMHD) code BATS-R-US with the implicit Particle-in-Cell (PIC) model iPIC3D. The PIC model can cover the regions where kinetic effects are most important, such as reconnection sites. The BATS-R-US code, on the other hand, can efficiently handle the rest of the computational domain where the MHD or Hall MHD description is sufficient. We will present our preliminary results and comparison with MESSENGER observations.
NASA Astrophysics Data System (ADS)
Mann, Ingrid; Krivov, Alexander; Kimura, Hiroshi
2000-08-01
General structure and composition of the near-solar dust cloud are investigated. Based on estimates for sources and transport of dust to the near-solar region, we derive a representative set of trajectories of dust grains by numerical integrations and obtain the spatial distribution of different dust populations within 10 solar radii ( R⊙) from the Sun. For the radial structure, we find the dust number density to be enhanced by a factor of 1 to 4 in a typical heliocentric distance zone with a width of 0.2 R⊙ in the sublimation region—the formation of a dust ring—depending on the materials and porosities considered. The excess density in the ring increases with increasing initial size for porous grains and decreases for compact ones. Non-zero eccentricities of the dust orbits decrease the enhancement. Moderate enhancements that we predict are consistent with eclipse observations, most of which have not shown any peak features in the F-corona brightness at several solar radii. We describe typical features of β-meteoroids formed by the sublimation of particles near the Sun and estimate the total mass loss due to this mechanism to range between 1 and 10 kg s -1. For the vertical structure of the dust cloud we show that grains larger than ˜10 μm in size keep in a disk with a typical thickness of tens degrees; grains with radii of several μm fill in a broader disk-like volume which is tilted off the ecliptic plane by a variable angle depending on the solar activity cycle; submicrometer-sized grains form a nearly spherical halo around the Sun with a radius of more than 10 R⊙. From our present knowledge we cannot exclude the existence of an additional spheroidal component of larger grains near the Sun, which depends on how effective long-period comets are as sources of dust. Estimates of absolute number densities and local fluxes of dust show that simple extrapolation of the interplanetary dust cloud into the solar vicinity does not describe the dust cloud
Sun Savvy Students: Free Teaching Resources from EPA's SunWise Program
ERIC Educational Resources Information Center
Hall-Jordan, Luke
2008-01-01
With summer in full swing and the sun is naturally on our minds, what better time to take advantage of a host of free materials provided by the U.S. Environmental Protection Agency's Sun Wise program. Sun Wise aims to teach students and teachers about the stratospheric ozone layer, ultraviolet (UV) radiation, and how to be safe while in the Sun.…
Seyler, C. E.; Martin, M. R.
2011-01-15
It is shown that the two-fluid model under a generalized Ohm's law formulation and the resistive magnetohydrodynamics (MHD) can both be described as relaxation systems. In the relaxation model, the under-resolved stiff source terms constrain the dynamics of a set of hyperbolic equations to give the correct asymptotic solution. When applied to the collisional two-fluid model, the relaxation of fast time scales associated with displacement current and finite electron mass allows for a natural transition from a system where Ohm's law determines the current density to a system where Ohm's law determines the electric field. This result is used to derive novel algorithms, which allow for multiscale simulation of low and high frequency extended-MHD physics. This relaxation formulation offers an efficient way to implicitly advance the Hall term and naturally simulate a plasma-vacuum interface without invoking phenomenological models. The relaxation model is implemented as an extended-MHD code, which is used to analyze pulsed power loads such as wire arrays and ablating foils. Two-dimensional simulations of pulsed power loads are compared for extended-MHD and MHD. For these simulations, it is also shown that the relaxation model properly recovers the resistive-MHD limit.
Increasing Sun Protection in Winter Outdoor Recreation
Walkosz, Barbara J.; Buller, David B.; Andersen, Peter A.; Scott, Michael D.; Dignan, Mark B.; Cutter, Gary R.; Maloy, Julie A.
2009-01-01
Background Unprotected and excessive exposure to ultraviolet radiation (UVR) is the primary risk factor for skin cancer. Design A pair-matched, group-randomized, pre-test/post-test, quasi-experimental design, with ski resorts as the unit of randomization, tested the effectiveness of Go Sun Smart, a multi-channel skin cancer prevention program. Independent samples of guests were taken at baseline (2001) and follow-up (2002); data were analyzed in 2006. Setting and Participants A total of 6516 adult guests at 26 ski resorts in the western U.S. and Canada were recruited, consented, and interviewed on chairlifts. This study was nested within an occupational intervention for ski resort workers. Intervention Ski resorts were pair-matched and randomized to receive Go Sun Smart, which consisted of print, electronic, visual, and interpersonal skin cancer prevention messages. Main Outcome Measures Sun-protection behaviors, sunburning, recall of sun-protection messages, and the association of message exposure to sun protection. Results The difference in recall of all sun-protection messages, messages on signs and posters, and the Go Sun Smart logo was significant between the intervention and control resorts. Reported use of sun-protection practices was higher by guests at intervention ski areas using more (a higher dose of) Go Sun Smart materials. Intervention-group guests who recalled a sun-safety message were more likely to practice sun safety than intervention-group guests who did not recall a message and control-group guests. Conclusions While the mere implementation of Go Sun Smart did not produce sun-safety improvements, Go Sun Smart appeared to be effective for guests who encountered and remembered it. Many factors can work against message exposure. Signage seemed to produce the greatest increase in exposure to sun-safety messages. PMID:18471586
Propagation Characteristics of Two Coronal Mass Ejections from the Sun Far into Interplanetary Space
NASA Astrophysics Data System (ADS)
Zhao, Xiaowei; Liu, Ying D.; Hu, Huidong; Wang, Rui
2017-03-01
Propagation of coronal mass ejections (CMEs) from the Sun far into interplanetary space is not well understood, due to limited observations. In this study we examine the propagation characteristics of two geo-effective CMEs, which occurred on 2005 May 6 and 13, respectively. Significant heliospheric consequences associated with the two CMEs are observed, including interplanetary CMEs (ICMEs) at the Earth and Ulysses, interplanetary shocks, a long-duration type II radio burst, and intense geomagnetic storms. We use coronagraph observations from SOHO/LASCO, frequency drift of the long-duration type II burst, in situ measurements at the Earth and Ulysses, and magnetohydrodynamic propagation of the observed solar wind disturbances at 1 au to track the CMEs from the Sun far into interplanetary space. We find that both of the CMEs underwent a major deceleration within 1 au and thereafter a gradual deceleration when they propagated from the Earth to deep interplanetary space, due to interactions with the ambient solar wind. The results also reveal that the two CMEs interacted with each other in the distant interplanetary space even though their launch times on the Sun were well separated. The intense geomagnetic storm for each case was caused by the southward magnetic fields ahead of the CME, stressing the critical role of the sheath region in geomagnetic storm generation, although for the first case there is a corotating interaction region involved.
BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN
Nelson, Nicholas J.; Toomre, Juri; Brown, Benjamin P.; Brun, Allan Sacha
2011-10-01
The current dynamo paradigm for the Sun and Sun-like stars places the generation site for strong toroidal magnetic structures deep in the solar interior. Sunspots and starspots on Sun-like stars are believed to arise when sections of these magnetic structures become buoyantly unstable and rise from the deep interior to the photosphere. Here, we present the first three-dimensional global magnetohydrodynamic (MHD) simulation in which turbulent convection, stratification, and rotation combine to yield a dynamo that self-consistently generates buoyant magnetic loops. We simulate stellar convection and dynamo action in a spherical shell with solar stratification, but rotating three times faster than the current solar rate. Strong wreaths of toroidal magnetic field are realized by dynamo action in the convection zone. By turning to a dynamic Smagorinsky model for subgrid-scale turbulence, we here attain considerably reduced diffusion in our simulation. This permits the regions of strongest magnetic field in these wreaths to rise toward the top of the convection zone via a combination of magnetic buoyancy instabilities and advection by convective giant cells. Such a global simulation yielding buoyant loops represents a significant step forward in combining numerical models of dynamo action and flux emergence.
Anisotropic energy transfers in quasi-static magnetohydrodynamic turbulence
Reddy, K. Sandeep; Kumar, Raghwendra; Verma, Mahendra K.
2014-10-15
We perform direct numerical simulations of quasi-static magnetohydrodynamic turbulence and compute various energy transfers including the ring-to-ring and conical energy transfers, and the energy fluxes of the perpendicular and parallel components of the velocity field. We show that the rings with higher polar angles transfer energy to ones with lower polar angles. For large interaction parameters, the dominant energy transfer takes place near the equator (polar angle θ≈(π)/2 ). The energy transfers are local both in wavenumbers and angles. The energy flux of the perpendicular component is predominantly from higher to lower wavenumbers (inverse cascade of energy), while that of the parallel component is from lower to higher wavenumbers (forward cascade of energy). Our results are consistent with earlier results, which indicate quasi two-dimensionalization of quasi-static magnetohydrodynamic flows at high interaction parameters.
Magnetohydrodynamics Accelerator Research into Advanced Hypersonics (MARIAH). Part 2
NASA Technical Reports Server (NTRS)
Baughman, Jack A.; Micheletti, David A.; Nelson, Gordon L.; Simmons, Gloyd A.
1997-01-01
This report documents the activities, results, conclusions and recommendations of the Magnetohydrodynamics Accelerator Research Into Advanced Hypersonics (MARIAH) Project in which the use of magnetohydrodynamics (MHD) technology is investigated for its applicability to augment hypersonic wind tunnels. The long range objective of this investigation is to advance the development of ground test facilities to support the development of hypervelocity flight vehicles. The MHD accelerator adds kinetic energy directly to the wind tunnel working fluid, thereby increasing its Mach number to hypervelocity levels. Several techniques for MHD augmentation, as well as other physical characteristics of the process are studied to enhance the overall performance of hypersonic wind tunnel design. Specific recommendations are presented to improve the effectiveness of ground test facilities. The work contained herein builds on nearly four decades of research and experimentation by the aeronautics ground test and evaluation community, both foreign and domestic.
Magnetohydrodynamics Accelerator Research Into Advanced Hypersonics (MARIAH). Part 1
NASA Technical Reports Server (NTRS)
Micheletti, David A.; Baughman, Jack A.; Nelson, Gordon L.; Simmons, Gloyd A.
1997-01-01
This report documents the activities, results, conclusions and recommendations of the Magnetohydrodynamics Accelerator Research Into Advanced Hypersonics (MARIAH) Project in which the use of magnetohydrodynamics (MHD) technology is investigated for its applicability to augment hypersonic wind tunnels. The long range objective of this investigation is to advance the development of ground test facilities to support the development of hypervelocity flight vehicles. The MHD accelerator adds kinetic energy directly to the wind tunnel working fluid, thereby increasing its Mach number to hypervelocity levels. Several techniques for MHD augmentation, as well as other physical characteristics of the process are studied to enhance the overall performance of hypersonic wind tunnel design. Specific recommendations are presented to improve the effectiveness of ground test facilities. The work contained herein builds on nearly four decades of research and experimentation by the aeronautics ground test and evaluation community, both foreign and domestic.
Dissipative, forced turbulence in two-dimensional magnetohydrodynamics
NASA Technical Reports Server (NTRS)
Fyfe, D.; Montgomery, D.; Joyce, G.
1976-01-01
The equations of motion for turbulent two-dimensional magnetohydrodynamic flows are solved in the presence of finite viscosity and resistivity, for the case in which external forces (mechanical and/or magnetic) act on the fluid. The goal is to verify the existence of a magnetohydrodynamic dynamo effect which is represented mathematically by a substantial back-transfer of mean square vector potential to the longest allowed Fourier wavelengths. External forces consisting of a random part plus a fraction of the value at the previous time step are employed, after the manner of Lilly for the Navier-Stokes case. The regime explored is that for which the mechanical and magnetic Reynolds numbers are in the region of 100 to 1000. The conclusions are that mechanical forcing terms alone cannot lead to dynamo action, but that dynamo action can result from either magnetic forcing terms or from both mechanical and magnetic forcing terms simultaneously.
General relativistic magneto-hydrodynamics with the Einstein Toolkit
NASA Astrophysics Data System (ADS)
Moesta, Philipp; Mundim, Bruno; Faber, Joshua; Noble, Scott; Bode, Tanja; Haas, Roland; Loeffler, Frank; Ott, Christian; Reisswig, Christian; Schnetter, Erik
2013-04-01
The Einstein Toolkit Consortium is developing and supporting open software for relativistic astrophysics. Its aim is to provide the core computational tools that can enable new science, broaden our community, facilitate interdisciplinary research and take advantage of petascale computers and advanced cyberinfrastructure. The Einstein Toolkit currently consists of an open set of over 100 modules for the Cactus framework, primarily for computational relativity along with associated tools for simulation management and visualization. The toolkit includes solvers for vacuum spacetimes as well as relativistic magneto-hydrodynamics. This talk will present the current capabilities of the Einstein Toolkit with a particular focus on recent improvements made to the general relativistic magneto-hydrodynamics modeling and will point to information how to leverage it for future research.
Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence
Donato, S.; Servidio, S.; Carbone, V.; Dmitruk, P.; Shay, M. A.; Matthaeus, W. H.; Cassak, P. A.
2012-09-15
The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.
Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field
NASA Technical Reports Server (NTRS)
Montgomery, D.; Turner, L.
1981-01-01
A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.
Numerical evaluation of high energy particle effects in magnetohydrodynamics
White, R.B.; Wu, Y.
1994-03-01
The interaction of high energy ions with magnetohydrodynamic modes is analyzed. A numerical code is developed which evaluates the contribution of the high energy particles to mode stability using orbit averaging of motion in either analytic or numerically generated equilibria through Hamiltonian guiding center equations. A dispersion relation is then used to evaluate the effect of the particles on the linear mode. Generic behavior of the solutions of the dispersion relation is discussed and dominant contributions of different components of the particle distribution function are identified. Numerical convergence of Monte-Carlo simulations is analyzed. The resulting code ORBIT provides an accurate means of comparing experimental results with the predictions of kinetic magnetohydrodynamics. The method can be extended to include self consistent modification of the particle orbits by the mode, and hence the full nonlinear dynamics of the coupled system.
Theory of magnetohydrodynamic instabilities excited by energetic particles in tokamaks
Chen, L. )
1994-05-01
The resonant excitations of high-[ital n] magnetohydrodynamic instabilities by the energetic ions/alpha particles in tokamaks are theoretically analyzed. Here, [ital n] is the toroidal mode number. The magnetohydrodynamic eigenmodes, typically, consist of two-scale structures; one corresponds to the singular ( inertial'') region and the other the regular (ideal) region. Due to the finite-size orbits, the energetic particle contributions in the singular region are suppressed. Analytical dispersion relations can be derived via the asymptotic matching analysis. The dispersion relations have the generic form of the fishbone'' dispersion relation [Phys. Rev. Lett. [bold 52], 1122 (1984)] and demonstrate, in particular, the existence of two types of modes; that is, the discrete gap mode and the energetic-particle continuum mode. Specific expressions are given for both the kinetic ballooning modes and the toroidal Alfven modes.
Flight Qualified Micro Sun Sensor
NASA Technical Reports Server (NTRS)
Liebe, Carl Christian; Mobasser, Sohrab; Wrigley, Chris; Schroeder, Jeffrey; Bae, Youngsam; Naegle, James; Katanyoutanant, Sunant; Jerebets, Sergei; Schatzel, Donald; Lee, Choonsup
2007-01-01
A prototype small, lightweight micro Sun sensor (MSS) has been flight qualified as part of the attitude-determination system of a spacecraft or for Mars surface operations. The MSS has previously been reported at a very early stage of development in NASA Tech Briefs, Vol. 28, No. 1 (January 2004). An MSS is essentially a miniature multiple-pinhole electronic camera combined with digital processing electronics that functions analogously to a sundial. A micromachined mask containing a number of microscopic pinholes is mounted in front of an active-pixel sensor (APS). Electronic circuits for controlling the operation of the APS, readout from the pixel photodetectors, and analog-to-digital conversion are all integrated onto the same chip along with the APS. The digital processing includes computation of the centroids of the pinhole Sun images on the APS. The spacecraft computer has the task of converting the Sun centroids into Sun angles utilizing a calibration polynomial. The micromachined mask comprises a 500-micron-thick silicon wafer, onto which is deposited a 57-nm-thick chromium adhesion- promotion layer followed by a 200-nm-thick gold light-absorption layer. The pinholes, 50 microns in diameter, are formed in the gold layer by photolithography. The chromium layer is thin enough to be penetrable by an amount of Sunlight adequate to form measurable pinhole images. A spacer frame between the mask and the APS maintains a gap of .1 mm between the pinhole plane and the photodetector plane of the APS. To minimize data volume, mass, and power consumption, the digital processing of the APS readouts takes place in a single field-programmable gate array (FPGA). The particular FPGA is a radiation- tolerant unit that contains .32,000 gates. No external memory is used so the FPGA calculates the centroids in real time as pixels are read off the APS with minimal internal memory. To enable the MSS to fit into a small package, the APS, the FPGA, and other components are mounted
Magnetic reversals in a simple model of magnetohydrodynamics.
Benzi, Roberto; Pinton, Jean-François
2010-07-09
We study a simple magnetohydrodynamical approach in which hydrodynamics and MHD turbulence are coupled in a shell model, with given dynamo constraints in the large scales. We consider the case of a low Prandtl number fluid for which the inertial range of the velocity field is much wider than that of the magnetic field. Random reversals of the magnetic field are observed and it shown that the magnetic field has a nontrivial evolution--linked to the nature of the hydrodynamics turbulence.
Investigation of a liquid-metal magnetohydrodynamic power system.
NASA Technical Reports Server (NTRS)
Elliott, D. G.; Hays, L. G.; Cerini, D. J.; Bogdanoff, D. W.
1972-01-01
Liquid-metal magnetohydrodynamic power conversion is being investigated for nuclear-electric propulsion. A liquid-metal MHD converter has no moving mechanical parts and requires a heat source temperature of only 1300 K. Cycle efficiencies of 5% to 8% for single-stage converters and 10% for multistage converters appear attainable. The specific weight of a 240 kWe MHD power plant has been estimated as 30 kg/kWe with shielding for unmanned science missions.
Exact solutions of the incompressible dissipative Hall magnetohydrodynamics
Xia, Zhenwei; Yang, Weihong
2015-03-15
By using analytical method, the exact solutions of the incompressible dissipative Hall magnetohydrodynamics (MHD) equations are derived. It is found that a phase difference may occur between the velocity and magnetic field fluctuations when the kinetic and magnetic Reynolds numbers are both very large. Since velocity and magnetic field fluctuations are both circular polarized, the phase difference makes them no longer parallel or anti-parallel like that in the incompressible ideal Hall MHD.
Analytical and experimental studies of the helical magnetohydrodynamic thruster design
Gilbert, J.B. II; Lin, T.F.
1994-12-31
This paper describes the results of analytical and experimental studies of a helical magnetohydrodynamic (MHD) seawater thruster using a 8-Tesla (T) solenoid magnet. The application of this work is in marine vehicle propulsion. Analytical models are developed to predict the performance of the helical MHD thruster in a closed-loop condition. The analytical results are compared with experimental data and good agreement is obtained.
Magnetohydrodynamic energy conversion by using convexly divergent channel
NASA Astrophysics Data System (ADS)
Murakami, Tomoyuki; Okuno, Yoshihiro
2009-12-01
We describe a magnetohydrodynamic (MHD) electrical power generator equipped with a convexly divergent channel, as determined through shock-tunnel-based experiments. The quality of MHD power-generating plasma and the energy conversion efficiency in the convexly divergent channel are compared with those from previous linearly divergent channel. The divergence enhancement in the channel upstream is effective for suppressing an excessive increase in static pressure, whereby notably high isentropic efficiency is achieved.
HARM: A Numerical Scheme for General Relativistic Magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Gammie, Charles, F.; McKinney, Jonathan C.; Tóth, Gábor
2012-09-01
HARM uses a conservative, shock-capturing scheme for evolving the equations of general relativistic magnetohydrodynamics. The fluxes are calculated using the Harten, Lax, & van Leer scheme. A variant of constrained transport, proposed earlier by Tóth, is used to maintain a divergence-free magnetic field. Only the covariant form of the metric in a coordinate basis is required to specify the geometry. On smooth flows HARM converges at second order.
Brown, Michael R.
2006-11-16
Project Title: Magnetohydrodynamic Particle Acceleration Processes: SSX Experiments, Theory, and Astrophysical Applications PI: Michael R. Brown, Swarthmore College The purpose of the project was to provide theoretical and modeling support to the Swarthmore Spheromak Experiment (SSX). Accordingly, the theoretical effort was tightly integrated into the SSX experimental effort. During the grant period, Michael Brown and his experimental collaborators at Swarthmore, with assistance from W. Matthaeus as appropriate, made substantial progress in understanding the physics SSX plasmas.
Magnetohydrodynamic energy conversion by using convexly divergent channel
Murakami, Tomoyuki; Okuno, Yoshihiro
2009-12-21
We describe a magnetohydrodynamic (MHD) electrical power generator equipped with a convexly divergent channel, as determined through shock-tunnel-based experiments. The quality of MHD power-generating plasma and the energy conversion efficiency in the convexly divergent channel are compared with those from previous linearly divergent channel. The divergence enhancement in the channel upstream is effective for suppressing an excessive increase in static pressure, whereby notably high isentropic efficiency is achieved.
Helicity Injection by Knotted Antennas into Electron Magnetohydrodynamical Plasmas
NASA Astrophysics Data System (ADS)
Rousculp, C. L.; Stenzel, R. L.
1997-08-01
A fully three-dimensional computer simulation of an ideal electron magnetohydrodynamical plasma is performed. By introducing various pulsed inductive antenna sources, magnetic helicity ( H = A˙B dV) injection is studied. Confirming experimental results, a simple loop provides no net helicity injection. Linked and knotted antennas, however, do inject helicity and preferentially radiate whistler wave packets parallel or antiparallel to the ambient magnetic field. Relative efficiencies of these antennas are reported as well as their unique directional properties.
NASA Astrophysics Data System (ADS)
Burke, B. J.; Kruger, S. E.; Hegna, C. C.; Zhu, P.; Snyder, P. B.; Sovinec, C. R.; Howell, E. C.
2010-03-01
A linear benchmark between the linear ideal MHD stability codes ELITE [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)], GATO [L. Bernard et al., Comput. Phys. Commun. 24, 377 (1981)], and the extended nonlinear magnetohydrodynamic (MHD) code, NIMROD [C. R. Sovinec et al.., J. Comput. Phys. 195, 355 (2004)] is undertaken for edge-localized (MHD) instabilities. Two ballooning-unstable, shifted-circle tokamak equilibria are compared where the stability characteristics are varied by changing the equilibrium plasma profiles. The equilibria model an H-mode plasma with a pedestal pressure profile and parallel edge currents. For both equilibria, NIMROD accurately reproduces the transition to instability (the marginally unstable mode), as well as the ideal growth spectrum for a large range of toroidal modes (n =1-20). The results use the compressible MHD model and depend on a precise representation of "ideal-like" and "vacuumlike" or "halo" regions within the code. The halo region is modeled by the introduction of a Lundquist-value profile that transitions from a large to a small value at a flux surface location outside of the pedestal region. To model an ideal-like MHD response in the core and a vacuumlike response outside the transition, separate criteria on the plasma and halo Lundquist values are required. For the benchmarked equilibria the critical Lundquist values are 108 and 103 for the ideal-like and halo regions, respectively. Notably, this gives a ratio on the order of 105, which is much larger than experimentally measured values using Te values associated with the top of the pedestal and separatrix. Excellent agreement with ELITE and GATO calculations are made when sharp boundary transitions in the resistivity are used and a small amount of physical dissipation is added for conditions very near and below marginal ideal stability.
Burke, B. J.; Kruger, S. E.; Hegna, C. C.; Zhu, P.; Snyder, P. B.; Sovinec, C. R.; Howell, E. C.
2010-03-15
A linear benchmark between the linear ideal MHD stability codes ELITE [H. R. Wilson et al., Phys. Plasmas 9, 1277 (2002)], GATO [L. Bernard et al., Comput. Phys. Commun. 24, 377 (1981)], and the extended nonlinear magnetohydrodynamic (MHD) code, NIMROD [C. R. Sovinec et al.., J. Comput. Phys. 195, 355 (2004)] is undertaken for edge-localized (MHD) instabilities. Two ballooning-unstable, shifted-circle tokamak equilibria are compared where the stability characteristics are varied by changing the equilibrium plasma profiles. The equilibria model an H-mode plasma with a pedestal pressure profile and parallel edge currents. For both equilibria, NIMROD accurately reproduces the transition to instability (the marginally unstable mode), as well as the ideal growth spectrum for a large range of toroidal modes (n=1-20). The results use the compressible MHD model and depend on a precise representation of 'ideal-like' and 'vacuumlike' or 'halo' regions within the code. The halo region is modeled by the introduction of a Lundquist-value profile that transitions from a large to a small value at a flux surface location outside of the pedestal region. To model an ideal-like MHD response in the core and a vacuumlike response outside the transition, separate criteria on the plasma and halo Lundquist values are required. For the benchmarked equilibria the critical Lundquist values are 10{sup 8} and 10{sup 3} for the ideal-like and halo regions, respectively. Notably, this gives a ratio on the order of 10{sup 5}, which is much larger than experimentally measured values using T{sub e} values associated with the top of the pedestal and separatrix. Excellent agreement with ELITE and GATO calculations are made when sharp boundary transitions in the resistivity are used and a small amount of physical dissipation is added for conditions very near and below marginal ideal stability.
Magnetohydrodynamic and gasdynamic theories for planetary bow waves
NASA Technical Reports Server (NTRS)
Spreiter, J. R.; Stahara, S. S.
1984-01-01
The observed properties of bow waves and the associated plasma flows are outlined, along with those features identified that can be described by a continuum magnetohydrodynamic flow theory as opposed to a more detailed multicomponent particle and field plasma theory. The primary objectives are to provide an account of the fundamental concepts and current status of the magnetohydrodynamic and gas dynamic theories for solar wind flow past planetary bodies. This includes a critical examination of: (1) the fundamental assumptions of the theories; (2) the various simplifying approximations introduced to obtain tractable mathematical problems; (3) the limitations they impose on the results; and (4) the relationship between the results of the simpler gas dynamic-frozen field theory and the more accurate but less completely worked out magnetohydrodynamic theory. Representative results of the various theories are presented and compared. A number of deficiencies, ambiguities, and suggestions for improvements are discussed, and several significant extensions of the theory required to provide comparable results for all planets, their satellites, and comets are noted.
Solar flare leaves sun quaking
NASA Astrophysics Data System (ADS)
1998-05-01
Dr. Alexander G. Kosovichev, a senior research scientist from Stanford University, and Dr. Valentina V. Zharkova from Glasgow (United Kingdom) University found the tell-tale seismic signature in data on the Sun's surface collected by the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO) spacecraft immediately following a moderate-sized flare on July 9, 1996. "Although the flare was a moderate one, it still released an immense amount of energy," said Dr. Craig Deforest, a researcher with the SOHO project. "The energy released is equal to completely covering the Earth's continents with a yard of dynamite and detonating it all at once." SOHO is a joint project of the European Space Agency and NASA. The finding is reported in the May 28 issue of the journal Nature, and is the subject of a press conference at the spring meeting of the American Geophysical Union in Boston, Mass., May 27. The solar quake that the science team recorded looks much like ripples spreading from a rock dropped into a pool of water. But over the course of an hour, the solar waves traveled for a distance equal to 10 Earth diameters before fading into the fiery background of the Sun's photosphere. Unlike water ripples that travel outward at a constant velocity, the solar waves accelerated from an initial speed of 22,000 miles per hour to a maximum of 250,000 miles per hour before disappearing. "People have looked for evidence of seismic waves from flares before, but they didn't have a theory so they didn't know where to look," says Kosovichev. Several years ago Kosovichev and Zharkova developed a theory that can explain how a flare, which explodes in space above the Sun's surface, can generate a major seismic wave in the Sun's interior. According to the currently accepted model of solar flares, the primary explosion creates high-energy electrons (electrically charged subatomic particles). These are funneled down into a magnetic flux tube, an invisible tube of magnetic
The Sun's New Exotic Neighbour
NASA Astrophysics Data System (ADS)
2006-03-01
Using ESO's Very Large Telescope in Chile, an international team of researchers [1] discovered a brown dwarf belonging to the 24th closest stellar system to the Sun. Brown dwarfs are intermediate objects that are neither stars nor planets. This object is the third closest brown dwarf to the Earth yet discovered, and one of the coolest, having a temperature of about 750 degrees Celsius. It orbits a very small star at about 4.5 times the mean distance between the Earth and the Sun. Its mass is estimated to be somewhere between 9 and 65 times the mass of Jupiter. At a time when astronomers are peering into the most distant Universe, looking at objects as far as 13 billion light-years away, one may think that our close neighbourhood would be very well known. Not so. Astronomers still find new star-like objects in our immediate vicinity. Using ESO's VLT, they just discovered a brown dwarf companion to the red star SCR 1845-6357, the 36th closest star to the Sun. ESO PR Photo 11/06 ESO PR Photo 11a/06 New Brown Dwarf in the Solar Neighbourhood (Artist's Impression) "This newly found brown dwarf is a valuable object because its distance is well known, allowing us to determine with precision its intrinsic brightness", said team member Markus Kasper (ESO). "Moreover, from its orbital motion, we should be able in a few years to estimate its mass. These properties are vital for understanding the nature of brown dwarfs." To discover this brown dwarf, the team used the high-contrast adaptive optics NACO Simultaneous Differential Imager (SDI [2]) on ESO's Very Large Telescope, an instrument specifically developed to search for extrasolar planets. The SDI camera enhances the ability of the VLT and its adaptive optics system to detect faint companions that would normally be lost in the glare of the primary star. In particular, the SDI camera provides additional, often very useful spectral information which can be used to determine a rough temperature for the object without follow
SLOW MAGNETOACOUSTIC WAVES OBSERVED ABOVE A QUIET-SUN REGION IN A DARK CAVITY
Liu Jiajia; Zhou Zhenjun; Wang Yuming; Liu Rui; Liao Chijian; Shen Chenglong; Zheng Huinan; Miao Bin; Su Zhenpeng; Wang, S.; Wang Bin E-mail: ymwang@ustc.edu.cn
2012-10-20
Waves play a crucial role in diagnosing the plasma properties of various structures in the solar corona and coronal heating. Slow magnetoacoustic (MA) waves are one of the important types of magnetohydrodynamic waves. In past decades, numerous slow MA waves were detected above active regions and coronal holes, but were rarely found elsewhere. Here, we investigate a 'tornado'-like structure consisting of quasi-periodic streaks within a dark cavity at about 40-110 Mm above a quiet-Sun region on 2011 September 25. Our analysis reveals that these streaks are actually slow MA wave trains. The properties of these wave trains, including phase speed, compression ratio, and kinetic energy density, are similar to those of the reported slow MA waves, except that the period of these waves is about 50 s, much shorter than the typical reported values (3-5 minutes).
Matt, Sean P.; Pinsonneault, Marc H.; Greene, Thomas P. E-mail: kmac@ucar.edu E-mail: thomas.p.greene@nasa.gov
2012-08-01
We use two-dimensional axisymmetric magnetohydrodynamic simulations to compute steady-state solutions for solar-like stellar winds from rotating stars with dipolar magnetic fields. Our parameter study includes 50 simulations covering a wide range of relative magnetic field strengths and rotation rates, extending from the slow- and approaching the fast-magnetic-rotator regimes. Using the simulations to compute the angular momentum loss, we derive a semi-analytic formulation for the external torque on the star that fits all of the simulations to a precision of a few percent. This formula provides a simple method for computing the magnetic braking of Sun-like stars due to magnetized stellar winds, which properly includes the dependence on the strength of the magnetic field, mass loss rate, stellar radius, surface gravity, and spin rate, and which is valid for both slow and fast rotators.
Probing the solar magnetic field with a Sun-grazing comet.
Downs, Cooper; Linker, Jon A; Mikií, Zoran; Riley, Pete; Schrijver, Carolus J; Saint-Hilaire, Pascal
2013-06-07
On 15 and 16 December 2011, Sun-grazing comet C/2011 W3 (Lovejoy) passed deep within the solar corona, effectively probing a region that has never been visited by spacecraft. Imaged from multiple perspectives, extreme ultraviolet observations of Lovejoy's tail showed substantial changes in direction, intensity, magnitude, and persistence. To understand this unique signature, we combined a state-of-the-art magnetohydrodynamic model of the solar corona and a model for the motion of emitting cometary tail ions in an embedded plasma. The observed tail motions reveal the inhomogeneous magnetic field of the solar corona. We show how these motions constrain field and plasma properties along the trajectory, and how they can be used to meaningfully distinguish between two classes of magnetic field models.
The UBVRI And Infrared Colour Indices Of The Sun And Sun-Like Stars
NASA Astrophysics Data System (ADS)
Tanriver, Mehmet; Özeren, Ferhat Fikri
2016-12-01
The Sun is not a point source, the photometric observational techniques that are utilised for observing other stars cannot be utilised for the Sun, meaning that it is difficult to derive its colours accurately for astronomical work from direct measurements in different passbands. The solar twins are the best choices because they are the stars that are ideally the same as the Sun in all parameters, and also, their colours are highly similar to those of the Sun. From the 60 articles on the Sun and Sun-like stars in the literature from 1964 until today, the solar colour indices in the optic and infrared regions have been estimated.
Parabolized Navier-Stokes Code for Computing Magneto-Hydrodynamic Flowfields
NASA Technical Reports Server (NTRS)
Mehta, Unmeel B. (Technical Monitor); Tannehill, J. C.
2003-01-01
This report consists of two published papers, 'Computation of Magnetohydrodynamic Flows Using an Iterative PNS Algorithm' and 'Numerical Simulation of Turbulent MHD Flows Using an Iterative PNS Algorithm'.
Zonal Flows Below the Sun's Convection: Analytic Approximation
NASA Technical Reports Server (NTRS)
Wolff, Charles L.; Mayr, Hans G.
2004-01-01
We have derived a simple analytic solution showing how the Sun's global oscillations (g-modes) can drive east-west flows at low latitude deep inside the Sun. This flow is analogous to the Quasi Biennial Oscillation in the Earth s upper atmosphere. It has an observed period of 1.3 years in the solar case but its cause was not known until we published an explanation in a Letter to the Editor a few months ago. Now we give full details of the model and show how it can be used to limit the range of g-modes that can be actively driving the reversing flows. A nonlinear feedback feature of the model is that the flow itself creates the turbulent dissipation that extracts momentum from the g-modes that, in turn, drives the flow.
Metabolomic analysis of sun exposed skin.
Randhawa, Manpreet; Southall, Michael; Samaras, Samantha Tucker
2013-08-01
It is very well known that exposure of skin to sun chronically accelerates the mechanism of aging as well as making it more susceptible toward skin cancer. This aspect of aging has been studied very well through genomics and proteomics tools. In this study we have used a metabolomic approach for the first time to determine the differences in the metabolome from full thickness skin biopsies from sun exposed and sun protected sites. We have primarily investigated the energy metabolism and the oxidative pathway in sun exposed skin. Biochemical pathway analysis revealed that energy metabolism in photoexposed skin is predominantly anaerobic. The study also validated the increased oxidative stress in skin.
Sun tracking solar energy collector
NASA Technical Reports Server (NTRS)
Perkins, G. S. (Inventor)
1978-01-01
A parabolic reflector is supported so that it can track the sun. The support for this reflector comprises an azimuth frame supported on two wheels and a central pivotal point which are positioned in a substantially triangular configuration. On top of the azimuth frame, there is provided an elevation frame. The reflector rides on wheels captured within curved rails. The wheels of the azimuth frame are driven by an azimuth actuator. The reflector structure is counterbalanced about its elevation axis by a pendulum cable system which is driven by a motor. At the focal point of the parabolic reflector, a heat engine or receiver is mounted independently on the reflector. Suitable means are provided for moving the reflector about its two axes.
NASA Technical Reports Server (NTRS)
Mullan, D. J.
1974-01-01
The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.
NASA Technical Reports Server (NTRS)
Cahalan, Robert
2002-01-01
We provide an overview of the impact of the Sun on the Earth atmosphere and climate system, focused on heating of Earth's atmosphere and oceans. We emphasize the importance of the spectral measurements of SIM and SOLSTICE- that we must know how solar variations are distributed over ultraviolet, visible, and infrared wavelengths, since these have separate characteristic influences on Earth's ozone layer, clouds, and upper layers of the oceans. Emphasis is also given to understanding both direct and indirect influences of the Sun on the Earth, which involve feedbacks between Earth's stratosphere, troposphere, and oceans, each with unique time scales, dynamics, chemistry, and biology, interacting non-linearly. Especially crucial is the role of all three phases of water on Earth, water vapor being the primary greenhouse gas in the atmosphere, the importance of trace gases such as CO2 arising from their absorption in the "water vapor window" at 800 - 1250/cm (12.5 to 8 microns). Melting of polar ice is one major response to the post-industrial global warming, enhanced due to "ice-albedo" feedback. Finally, water in liquid form has a major influence due to cloud albedo feedback, and also due to the oceans' absorption of solar radiation, particularly at visible wavelengths, through the visible "liquid water window" that allows penetration of visible light deep into the mixed layer, while nearby ultraviolet and infrared wavelengths do not penetrate past the upper centimeter ocean surface skin layer. A large fraction of solar energy absorbed by the oceans goes into the latent heat of evaporation. Thus the solar heating of the atmosphere-ocean system is strongly coupled through the water cycle of evaporation, cloud formation, precipitation, surface runoff and ice formation, to Earth's energy budget and climate, each different climate component responding to variations in different solar spectral bands, at ultraviolet, visible and infrared wavelengths.
NASA Technical Reports Server (NTRS)
1981-01-01
The estimated plant capital cost for a coal fired 200 MWE electric generating plant with open cycle magnetohydrodynamics is divided into principal accounts based on Federal Energy Regulatory Commision account structure. Each principal account is defined and its estimated cost subdivided into identifiable and major equipment systems. The cost data sources for compiling the estimates, cost parameters, allotments, assumptions, and contingencies, are discussed. Uncertainties associated with developing the costs are quantified to show the confidence level acquired. Guidelines established in preparing the estimated costs are included. Based on an overall milestone schedule related to conventional power plant scheduling experience and starting procurement of MHD components during the preliminary design phase there is a 6 1/2-year construction period. The duration of the project from start to commercial operation is 79 months. The engineering phase of the project is 4 1/2 years; the construction duration following the start of the man power block is 37 months.
Buller, David B.; Berwick, Marianne; Lantz, Kathy; Buller, Mary Klein; Shane, James; Kane, Ilima; Liu, Xia
2014-01-01
Importance Mobile smart phones are rapidly emerging as an effective means of communicating with many Americans. Using mobile applications, they can access remote databases, track time and location, and integrate user input to provide tailored health information. Objective A smart phone mobile application providing personalized, real-time sun protection advice was evaluated in a randomized trial. Design The trial was conducted in 2012 and had a randomized pretest-posttest controlled design with a 10-week follow-up. Setting Data was collected from a nationwide population-based survey panel. Participants The trial enrolled a sample of n=604 non-Hispanic and Hispanic adults from the Knowledge Panel® aged 18 or older who owned an Android smart phone. Intervention The mobile application provided advice on sun protection (i.e., protection practices and risk of sunburn) and alerts (to apply/reapply sunscreen and get out of the sun), hourly UV Index, and vitamin D production based on the forecast UV Index, phone's time and location, and user input. Main Outcomes and Measures Percent of days using sun protection and time spent outdoors (days and minutes) in the midday sun and number of sunburns in the past 3 months were collected. Results Individuals in the treatment group reported more shade use but less sunscreen use than controls. Those who used the mobile app reported spending less time in the sun and using all protection behaviors combined more. Conclusions and Relevance The mobile application improved some sun protection. Use of the mobile application was lower than expected but associated with increased sun protection. Providing personalized advice when and where people are in the sun may help reduce sun exposure. PMID:25629710
THE INFRARED COLORS OF THE SUN
Casagrande, L.; Asplund, M.; Ramirez, I.; Melendez, J.
2012-12-10
Solar infrared colors provide powerful constraints on the stellar effective temperature scale, but they must be measured with both accuracy and precision in order to do so. We fulfill this requirement by using line-depth ratios to derive in a model-independent way the infrared colors of the Sun, and we use the latter to test the zero point of the Casagrande et al. effective temperature scale, confirming its accuracy. Solar colors in the widely used Two Micron All Sky Survey (2MASS) JHK{sub s} and WISE W1-4 systems are provided: (V - J){sub Sun} = 1.198, (V - H){sub Sun} = 1.484, (V - K{sub s} ){sub Sun} = 1.560, (J - H){sub Sun} = 0.286, (J - K{sub s} ){sub Sun} = 0.362, (H - K{sub s} ){sub Sun} = 0.076, (V - W1){sub Sun} = 1.608, (V - W2){sub Sun} = 1.563, (V - W3){sub Sun} = 1.552, and (V - W4){sub Sun} = 1.604. A cross-check of the effective temperatures derived implementing 2MASS or WISE magnitudes in the infrared flux method confirms that the absolute calibration of the two systems agrees within the errors, possibly suggesting a 1% offset between the two, thus validating extant near- and mid-infrared absolute calibrations. While 2MASS magnitudes are usually well suited to derive T{sub eff}, we find that a number of bright, solar-like stars exhibit anomalous WISE colors. In most cases, this effect is spurious and can be attributed to lower-quality measurements, although for a couple of objects (3% {+-} 2% of the total sample) it might be real, and may hint at the presence of warm/hot debris disks.
ERIC Educational Resources Information Center
Gritz, Ellen R.; Tripp, Mary K.; James, Aimee S.; Harrist, Ronald B.; Mueller, Nancy H.; Chamberlain, Robert M.; Parcel, Guy S.
2007-01-01
The preschool is an important yet understudied setting for sun-protection interventions. This study evaluates the effects of Sun Protection is Fun! (SPF) on preschool staff behavioral and psychosocial outcomes related to protecting children from sun exposure. Twenty preschools participated in a 2-year, group-randomized trial to evaluate SPF, a…
Non-melanoma skin cancer, sun exposure and sun protection.
Calzavara-Pinton, P; Ortel, B; Venturini, M
2015-08-01
The incidence of skin tumors including squamous cell carcinoma (SCC), and its biological precursor, the actinic keratosis, and basal cell carcinoma (BCC) often named together non-melanoma skin cancer (NMSC) is growing all over the world in people of Caucasian ancestry. A plenty of clinical and epidemiological studies have demonstrated the causal relationship with high cumulative solar dosages and number of sunburns, although the hazard may be different for different tumors according to the modalities of ultraviolet (UV) exposure. BCC is much more strongly related to measures of intermittent ultraviolet exposure (particularly those of childhood or adolescence) than to measures of cumulative exposure. In contrast, SCC is more strongly related to constant or cumulative sun exposure. Photobiological studies have clarified that sunlight and UVB radiation are complete carcinogens for AK and SCC although the relationship with UVA exposure is much less known. Also the likelihood of BCC has been related to either sunburns and high lifetime solar, UVA and UVB cumulative doses but the pathogenetic pathways of both UVB and UVA radiation for BCC development need to be clarified so far. The lack of a complete knowledge of the photocarcinogenic pathways of keratinocytes has contributed to the limited results of solar photoprotection strategies, beside the limitations of the available sunscreens and present EU regulations.
NASA Astrophysics Data System (ADS)
Pochron, Sharon T.
Do free-ranging baboons avoid traveling towards the sun? Sun avoidance, in addition to resource and predator locations, may influence troop movement and non-random use of the home range. This paper investigates how sun avoidance, as measured by facial exposure to sunlight, influences directional choices. It hypothesizes that baboons should avoid the sun in the hot, dry season and show indifference to it in the cool, lush season. This paper also hypothesizes that baboons employ sun-avoidance behaviors more while they forage or travel to resting sites than when they travel to foraging sites or engage in active social behaviors; lastly this paper hypothesizes that sun altitude, temperature, humidity, and cloud cover influence sun-avoidance behavior. Using focal-animal techniques on 21 males from free-ranging baboon troops, I collected locational data, accurate to within 1.6 m, over 15 months. I calculated the difference between baboon bearings and the sun's azimuth in angular degrees. Both linear and circular statistics indicate that baboons put significantly (P<0.01) more than 90° between their bearing and the sun's azimuth under certain conditions. Contrary to hypotheses based on the detrimental effects of insolation, baboons in the cool, lush season avoid the sun, while baboons in the hot, dry season do not. In the lush season, the extent to which baboons avoid the sun does not depend on their other behaviors. Dry-season baboons demonstrate stronger sun avoidance while resting than when engaged in other behaviors. Finally, in the dry season, temperature drives sun avoidance; humidity drives it in the lush season.
Pochron, S T
2000-09-01
Do free-ranging baboons avoid traveling towards the sun? Sun avoidance, in addition to resource and predator locations, may influence troop movement and non-random use of the home range. This paper investigates how sun avoidance, as measured by facial exposure to sunlight, influences directional choices. It hypothesizes that baboons should avoid the sun in the hot, dry season and show indifference to it in the cool, lush season. This paper also hypothesizes that baboons employ sun-avoidance behaviors more while they forage or travel to resting sites than when they travel to foraging sites or engage in active social behaviors; lastly this paper hypothesizes that sun altitude, temperature, humidity, and cloud cover influence sun-avoidance behavior. Using focal-animal techniques on 21 males from free-ranging baboon troops, I collected locational data, accurate to within 1.6 m, over 15 months. I calculated the difference between baboon bearings and the sun's azimuth in angular degrees. Both linear and circular statistics indicate that baboons put significantly (P<0.01) more than 90 degrees between their bearing and the sun's azimuth under certain conditions. Contrary to hypotheses based on the detrimental effects of insolation, baboons in the cool, lush season avoid the sun, while baboons in the hot, dry season do not. In the lush season, the extent to which baboons avoid the sun does not depend on their other behaviors. Dry-season baboons demonstrate stronger sun avoidance while resting than when engaged in other behaviors. Finally, in the dry season, temperature drives sun avoidance; humidity drives it in the lush season.
Sun protection in children: realities and challenges.
Gilaberte, Y; Carrascosa, J M
2014-04-01
One of the main goals of all skin cancer prevention campaigns is to protect children from ultraviolet radiation. However, little is known about how sun exposure risks differ between adults and children or about how these risks are best managed. Children's skin is more susceptible to sun damage for a number of reasons, including certain anatomical and functional aspects in children under 2 years of age and habits that predispose to greater sun exposure during the first 2 decades of life. Oil-based emulsions containing inorganic filters appear to be safest sunscreens for children, although the addition of certain organic filters is necessary to achieve a sun protection factor of 50. Oxybenzone, and probably also octocrylene, should be avoided in sunscreens for children. Sunscreen use should be part of an overall sun protection strategy that includes avoidance of exposure to midday sun and the use of protective clothing and hats. The above considerations justify the implementation of primary prevention campaigns focused on sun protection education for children and the continuation of basic and epidemiological research into specific sun protection strategies and sunscreens for each age group.
Harvesting the Sun's Energy with Antennas
INL
2008-05-28
Researchers at Idaho National Laboratory, along with partners at Microcontinuum Inc. (Cambridge, MA) and Patrick Pinhero of the University of Missouri, are developing a novel way to collect energy from the sun with a technology that could potentially cost pennies a yard, be imprinted on flexible materials and still draw energy after the sun has set.
Space Science in Action: Sun [Videotape].
ERIC Educational Resources Information Center
1999
This videotape recording shows students what the sun is all about--how big it is, what it is made of, how old it is, and how long it is believed it will continue to burn. Students examine the individual layers of the sun and learn about solar activities, including sunspots, solar flares, and prominences. A hands-on activity guides students in…
ERIC Educational Resources Information Center
Fry, Tom
2002-01-01
Describes easy-to-implement strategies parents can use to ensure their children's safety in the sun and avoid skin cancer, which is the most prevalent form of cancer in United States. Suggestions include: limit the amount of time spent in the sun, wear protective clothing, use sunscreening agents, and have knowledge of skin cancer and its…
EFFECT OF THE SUN UPON ANTENNA TEMPERATURE
temperature distributions over the sun at several frequencies are presented. The method by which antenna temperature is evaluated, using the Philco...calculate the variation of carrier-to-noise ratio as an antenna scans toward the sun while receiving signals from a deep-space probe and from a random-orbit satellite.
Harvesting the Sun's Energy with Antennas
INL
2016-07-12
Researchers at Idaho National Laboratory, along with partners at Microcontinuum Inc. (Cambridge, MA) and Patrick Pinhero of the University of Missouri, are developing a novel way to collect energy from the sun with a technology that could potentially cost pennies a yard, be imprinted on flexible materials and still draw energy after the sun has set.
Some Basic Aspects of Magnetohydrodynamic Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Hess, Robert V.
1959-01-01
An appraisal is made of existing solutions of magnetohydrodynamic boundary-layer equations for stagnation flow and flat-plate flow, and some new solutions are given. Since an exact solution of the equations of magnetohydrodynamics requires complicated simultaneous treatment of the equations of fluid flow and of electromagnetism, certain simplifying assumptions are generally introduced. The full implications of these assumptions have not been brought out properly in several recent papers. It is shown in the present report that for the particular law of deformation which the magnetic lines are assumed to follow in these papers a magnet situated inside the missile nose would not be able to take up any drag forces; to do so it would have to be placed in the flow away from the nose. It is also shown that for the assumption that potential flow is maintained outside the boundary layer, the deformation of the magnetic lines is restricted to small values. The literature contains serious disagreements with regard to reductions in heat-transfer rates due to magnetic action at the nose of a missile, and these disagreements are shown to be mainly due to different interpretations of reentry conditions rather than more complicated effects. In the present paper the magnetohydrodynamic boundary-layer equation is also expressed in a simple form that is especially convenient for physical interpretation. This is done by adapting methods to magnetic forces which in the past have been used for forces due to gravitational or centrifugal action. The simplified approach is used to develop some new solutions of boundary-layer flow and to reinterpret certain solutions existing in the literature. An asymptotic boundary-layer solution representing a fixed velocity profile and shear is found. Special emphasis is put on estimating skin friction and heat-transfer rates.
New Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence
NASA Astrophysics Data System (ADS)
Banerjee, Supratik; Galtier, Sebastien
2016-04-01
Hall magnetohydrodynamics is a mono-fluid plasma model appropriate for probing Final{some of the} physical processes (other than pure kinetic effects) at length scales smaller than the scales of standard MHD. In sub-ionic space plasma turbulence (e.g. the solar wind) this fluid model has been proved to be useful. Three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses three inviscid invariants which are the total energy, the magnetic helicity and the generalized helicity. In this presentation, we would like to discuss new exact relations for helicities (magnetic helicities and generalized helicities) which are derived for homogeneous stationary (not necessarily isotropic) Hall MHD turbulence (and also for its inertialess electron MHD limit) in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e. the scalar product of two different increments and are written simply as ηM = di < δ ( {b} × {j}) \\cdot δ {b} >, with ηM the average magnetic helicity flux rate, {b} the magnetic field, {j} the current and ± ηG = < δ ( {v} × {Ω} ) \\cdot δ {Ω} > , with ηM the average generalized helicity flux rate, {v} the fluid velocity and {Ω} = {b} + dI {ω} being the generalized helicity where ω is simply the fluid vorticity ( = nabla × {v}). It provides, therefore, a direct measurement of the dissipation rates for the corresponding helicities even in case of an anisotropic plasma turbulence. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations while the magnetic helicity cascade is linked to the right polarized fluctuations. The newly derived relations also show that like energy, a non-zero helicity flux can only be associated to a departure of Beltrami flow state. {Reference} S. Banerjee & S. Galtier, {Chiral Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence} (submitted).
THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF PLANET MIGRATION IN TURBULENT STRATIFIED DISKS
Uribe, A. L.; Klahr, H.; Flock, M.; Henning, Th.
2011-08-01
We performed three-dimensional magnetohydrodynamic simulations of planet migration in stratified disks using the Godunov code PLUTO, where the disk is turbulent due to the magnetorotational instability. We study the migration for planets with different planet-star mass ratios q = M{sub p} /M{sub s} . In agreement with previous studies, for the low-mass planet cases (q = 5 x 10{sup -6} and 10{sup -5}), migration is dominated by random fluctuations in the torque. For a Jupiter-mass planet (q = M{sub p} /M{sub s} = 10{sup -3} for M{sub s} = 1M{sub sun}), we find a reduction of the magnetic stress inside the orbit of the planet and around the gap region. After an initial stage where the torque on the planet is positive, it reverses and we recover migration rates similar to those found in disks where the turbulent viscosity is modeled by an {alpha} viscosity. For the intermediate-mass planets (q = 5 x 10{sup -5}, 10{sup -4}, and 2 x 10{sup -4}), we find a new and so far unexpected behavior. In some cases they experience sustained and systematic outward migration for the entire duration of the simulation. For this case, the horseshoe region is resolved and torques coming from the corotation region can remain unsaturated due to the stresses in the disk. These stresses are generated directly by the magnetic field. The magnitude of the horseshoe drag can overcome the negative Lindblad contribution when the local surface density profile is flat or increasing outward, which we see in certain locations in our simulations due to the presence of a zonal flow. The intermediate-mass planet is migrating radially outward in locations where there is a positive gradient of a pressure bump (zonal flow).
NASA Astrophysics Data System (ADS)
Usmanov, Arcadi V.; Goldstein, Melvyn L.; Matthaeus, William H.
2014-06-01
We have developed a three-fluid, three-dimensional magnetohydrodynamic solar wind model that incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating. The solar wind plasma is described as a system of co-moving solar wind protons, electrons, and interstellar pickup protons, with separate energy equations for each species. Numerical steady-state solutions of Reynolds-averaged solar wind equations coupled with turbulence transport equations for turbulence energy, cross helicity, and correlation length are obtained by the time relaxation method in the corotating with the Sun frame of reference in the region from 0.3 to 100 AU (but still inside the termination shock). The model equations include the effects of electron heat conduction, Coulomb collisions, photoionization of interstellar hydrogen atoms and their charge exchange with the solar wind protons, turbulence energy generation by pickup protons, and turbulent heating of solar wind protons and electrons. The turbulence transport model is based on the Reynolds decomposition and turbulence phenomenologies that describe the conversion of fluctuation energy into heat due to a turbulent cascade. In addition to using separate energy equations for the solar wind protons and electrons, a significant improvement over our previous work is that the turbulence model now uses an eddy viscosity approximation for the Reynolds stress tensor and the mean turbulent electric field. The approximation allows the turbulence model to account for driving of turbulence by large-scale velocity gradients. Using either a dipole approximation for the solar magnetic field or synoptic solar magnetograms from the Wilcox Solar Observatory for assigning boundary conditions at the coronal base, we apply the model to study the global structure of the solar wind and its three-dimensional properties, including embedded turbulence, heating, and acceleration throughout the heliosphere. The model results are
Usmanov, Arcadi V.; Matthaeus, William H.; Goldstein, Melvyn L.
2014-06-10
We have developed a three-fluid, three-dimensional magnetohydrodynamic solar wind model that incorporates turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating. The solar wind plasma is described as a system of co-moving solar wind protons, electrons, and interstellar pickup protons, with separate energy equations for each species. Numerical steady-state solutions of Reynolds-averaged solar wind equations coupled with turbulence transport equations for turbulence energy, cross helicity, and correlation length are obtained by the time relaxation method in the corotating with the Sun frame of reference in the region from 0.3 to 100 AU (but still inside the termination shock). The model equations include the effects of electron heat conduction, Coulomb collisions, photoionization of interstellar hydrogen atoms and their charge exchange with the solar wind protons, turbulence energy generation by pickup protons, and turbulent heating of solar wind protons and electrons. The turbulence transport model is based on the Reynolds decomposition and turbulence phenomenologies that describe the conversion of fluctuation energy into heat due to a turbulent cascade. In addition to using separate energy equations for the solar wind protons and electrons, a significant improvement over our previous work is that the turbulence model now uses an eddy viscosity approximation for the Reynolds stress tensor and the mean turbulent electric field. The approximation allows the turbulence model to account for driving of turbulence by large-scale velocity gradients. Using either a dipole approximation for the solar magnetic field or synoptic solar magnetograms from the Wilcox Solar Observatory for assigning boundary conditions at the coronal base, we apply the model to study the global structure of the solar wind and its three-dimensional properties, including embedded turbulence, heating, and acceleration throughout the heliosphere. The model results are
Numerical solutions of the three-dimensional magnetohydrodynamic alpha model.
Mininni, Pablo D; Montgomery, David C; Pouquet, Annick
2005-04-01
We present direct numerical simulations and alpha -model simulations of four familiar three-dimensional magnetohydrodynamic (MHD) turbulence effects: selective decay, dynamic alignment, inverse cascade of magnetic helicity, and the helical dynamo effect. The MHD alpha model is shown to capture the long-wavelength spectra in all these problems, allowing for a significant reduction of computer time and memory at the same kinetic and magnetic Reynolds numbers. In the helical dynamo, not only does the alpha model correctly reproduce the growth rate of magnetic energy during the kinematic regime, it also captures the nonlinear saturation level and the late generation of a large scale magnetic field by the helical turbulence.
Simakov, Andrei N; Chacón, L
2008-09-05
Dissipation-independent, or "fast", magnetic reconnection has been observed computationally in Hall magnetohydrodynamics (MHD) and predicted analytically in electron MHD. However, a quantitative analytical theory of reconnection valid for arbitrary ion inertial lengths, d{i}, has been lacking and is proposed here for the first time. The theory describes a two-dimensional reconnection diffusion region, provides expressions for reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and d{i}. It also confirms the electron MHD prediction that both open and elongated diffusion regions allow fast reconnection, and reveals strong dependence of the reconnection rates on d{i}.
Multirail electromagnetic launcher powered from a pulsed magnetohydrodynamic generator
NASA Astrophysics Data System (ADS)
Afonin, A. G.; Butov, V. G.; Panchenko, V. P.; Sinyaev, S. V.; Solonenko, V. A.; Shvetsov, G. A.; Yakushev, A. A.
2015-09-01
The operation of an electromagnetic multirail launcher of solids powered from a pulsed magnetohydrodynamic (MHD) generator is studied. The plasma flow in the channel of the pulsed MHD generator and the possibility of launching solids in a rapid-fire mode of launcher operation are considered. It is shown that this mode of launcher operation can be implemented by matching the plasma flow dynamics in the channel of the pulsed MHD generator and the launching conditions. It is also shown that powerful pulsed MHD generators can be used as a source of electrical energy for rapid-fire electromagnetic rail launchers operating in a burst mode.
Two-dimensional magnetohydrodynamic turbulence - Cylindrical, non-dissipative model
NASA Technical Reports Server (NTRS)
Montgomery, D.; Vahala, G.
1979-01-01
Incompressible magnetohydrodynamic turbulence is treated in the presence of cylindrical boundaries which are perfectly conducting and rigidly smooth. The model treated is non-dissipative and two-dimensional, the variation of all quantities in the axial direction being ignored. Equilibrium Gibbs ensemble predictions are explored assuming the constraint of constant axial current (appropriate to tokamak operation). No small-amplitude approximations are made. The expectation value of the turbulent kinetic energy is found to approach zero for the state of maximum mean-square vector potential to energy ratio. These are the only states for which large velocity fluctuations are not expected.
Hall current effects in the Lewis magnetohydrodynamic generator
NASA Technical Reports Server (NTRS)
Nichols, L. D.; Sovie, R. J.
1972-01-01
Data obtained in a magnetohydrodynamic generator are compared with theoretical values calculated by using the Dzung theory. The generator was operated with cesium-seeded argon as the working fluid. The gas temperature varied from 1800 to 2100 K, the gas pressure from 19 to 22 N/sq cm, the Mach number from 0.3 to 0.5, and the magnetic field strength from 0.2 to 1.6 T. The analysis indicates that there is incomplete seed vaporization and that Hall current shorting paths (through the working fluid to ground at both the entrance and exit of the channel) limit generator performance.
Magnetohydrodynamic turbulence: Generalized formulation and extension to compressible cases
Shivamoggi, Bhimsen K.
2008-06-15
A general framework that incorporates the Iroshnikov-Kraichnan (IK) and Goldreich-Sridhar (GS) phenomenalogies of magnetohydrodynamic (MHD) turbulence is developed. This affords a clarification of the regimes of validity of the IK and GS models and hence help resolve some controversies on this aspect. This general formulation appears to have a certain robustness as revealed here by its form invariance with respect to inclusion of compressible effects. Generalizations of the IK and GS spectra to compressible MHD turbulence are given. These two branches are shown to merge with the MHD shockwave spectrum, as to be expected, in the infinite compressibility limit.
Energy decay laws in strongly anisotropic magnetohydrodynamic turbulence.
Bigot, Barbara; Galtier, Sébastien; Politano, Hélène
2008-02-22
We investigate the influence of a uniform magnetic field B(0)=B(0)e( parallel) on energy decay laws in incompressible magnetohydrodynamic (MHD) turbulence. The nonlinear transfer reduction along B(0) is included in a model that distinguishes parallel and perpendicular directions, following a phenomenology of Kraichnan. We predict a slowing down of the energy decay due to anisotropy in the limit of strong B(0), with distinct power laws for energy decay of shear- and pseudo-Alfvén waves. Numerical results from the kinetic equations of Alfvén wave turbulence recover these predictions, and MHD numerical results clearly tend to follow them in the lowest perpendicular planes.
The Analysis of a Vortex Type Magnetohydrodynamic Induction Generator
NASA Technical Reports Server (NTRS)
Lengyel, L. L.
1962-01-01
Consideration it is given to the performance to the characteristics of an AC magnetohydrodynamic power generator, A rotating magnetic field is imposed on the vortex flow of an electrically conducting fluid, which is injected tangentially into an annulus formed by two nonconducting concentric cylinders and two nonconducting end plates. A perturbation technique is used to determine the two dimensional velocity and three dimensional electromagnetic field and current distributions. Finally, the generated power, the ohmic losses, the effective power and the electrical efficiency of the converter system are calculated.
Stability of certain families of ideal magnetohydrodynamic equilibria.
Núñez, Manuel
2003-01-01
The equations of ideal magnetohydrodynamic equilibria posses a number of symmetries that may be used to generate a family of hitherto unknown equilibria if there exists a foliation of the original one by magnetic surfaces. In addition to the possibility of producing analytic equilibria from old ones, this family is studied to find among its members those with minimal energy, those lasting longer under slightly resistive conditions, and those linearly stable. It is shown that in general none of these properties implies any other, thus clarifying the difference among these concepts.
Plasma relaxation and topological aspects in Hall magnetohydrodynamics
Shivamoggi, B. K.
2012-07-15
Parker's formulation of isotopological plasma relaxation process in magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient {alpha} in the Hall MHD Beltrami condition turns out now to be proportional to the potential vorticity. The Hall MHD Beltrami condition becomes equivalent to the potential vorticity conservation equation in two-dimensional (2D) hydrodynamics if the Hall MHD Lagrange multiplier {beta} is taken to be proportional to the potential vorticity as well. The winding pattern of the magnetic field lines in Hall MHD then appears to evolve in the same way as potential vorticity lines in 2D hydrodynamics.
Classical and semirelativistic magnetohydrodynamics with anisotropic ion pressure
NASA Astrophysics Data System (ADS)
Meng, Xing; Tóth, Gábor; Sokolov, Igor V.; Gombosi, Tamas I.
2012-05-01
We study the magnetohydrodynamics (MHD) equations with anisotropic ion pressure and isotropic electron pressure under both the classical and semirelativistic approximations in order to develop a numerical model. The dispersion relation as well as the characteristic wave speeds are derived. In addition to the exact wave speed solutions, we also provide efficient approximate formulas for the semirelativistic magnetosonic speeds. The equations are discretized with the Rusanov and Harten-Lax-van Leer numerical schemes and implemented into the BATS-R-US MHD code. We perform a set of verification tests.
Magnetohydrodynamic waves and coronal seismology: an overview of recent results.
De Moortel, Ineke; Nakariakov, Valery M
2012-07-13
Recent observations have revealed that magnetohydrodynamic (MHD) waves and oscillations are ubiquitous in the solar atmosphere, with a wide range of periods. We give a brief review of some aspects of MHD waves and coronal seismology that have recently been the focus of intense debate or are newly emerging. In particular, we focus on four topics: (i) the current controversy surrounding propagating intensity perturbations along coronal loops, (ii) the interpretation of propagating transverse loop oscillations, (iii) the ongoing search for coronal (torsional) Alfvén waves, and (iv) the rapidly developing topic of quasi-periodic pulsations in solar flares.
Generalized similarity in finite range solar wind magnetohydrodynamic turbulence.
Chapman, S C; Nicol, R M
2009-12-11
Extended or generalized similarity is a ubiquitous but not well understood feature of turbulence that is realized over a finite range of scales. The ULYSSES spacecraft solar polar passes at solar minimum provide in situ observations of evolving anisotropic magnetohydrodynamic turbulence in the solar wind under ideal conditions of fast quiet flow. We find a single generalized scaling function characterizes this finite range turbulence and is insensitive to plasma conditions. The recent unusually inactive solar minimum--with turbulent fluctuations down by a factor of approximately 2 in power--provides a test of this invariance.
Microwave imaging of magnetohydrodynamic instabilities in fusion plasma
NASA Astrophysics Data System (ADS)
Sabot, Roland; Elbèze, Didier; Lee, Woochang; Nam, Yoonbum; Park, Hyeon; Shen, Junsong; Yun, Gunsu; Choi, Minjun; Giacalone, Jean-Claude; Nicolas, Timothée; Bottereau, Christine; Clairet, Frédéric; Lotte, Philippe; Molina, Diego
2016-11-01
Microwave imaging diagnostics are extremely useful for observing magnetohydrodynamic (MHD) instabilities in magnetic fusion plasmas. Two imaging diagnostics will be available on the WEST tokamak. A method was developed to reconstruct electron density maps from electron density profiles measured by ultrafast reflectometry, a technique based on FM-CW radar principle. It relies on plasma rotation to perform 2D reconstruction. An Electron Cyclotron Emission Imaging (ECEI) diagnostic will image directly the temperature fluctuations. It will be equivalent to 24 stacked vertically radiometers, each probing a spot of few centimetres. These two complementary techniques will contribute to the validation of MHD models.
Helicity Injection by Knotted Antennas into Electron Magnetohydrodynamical Plasmas
Rousculp, C.L.; Stenzel, R.L.
1997-08-01
A fully three-dimensional computer simulation of an ideal electron magnetohydrodynamical plasma is performed. By introducing various pulsed inductive antenna sources, magnetic helicity (H={bold A}{center_dot}{bold B}dV) injection is studied. Confirming experimental results, a simple loop provides no net helicity injection. Linked and knotted antennas, however, do inject helicity and preferentially radiate whistler wave packets parallel or antiparallel to the ambient magnetic field. Relative efficiencies of these antennas are reported as well as their unique directional properties. {copyright} {ital 1997} {ital The American Physical Society}
Spectral method for obtaining three-dimensional magnetohydrodynamic equilibria
Hirshman, S.P.; Lee, D.K.
1985-07-01
A description is given of a new code, MOMCON (spectral moments with constraints), that obtains three-dimensional ideal magnetohydrodynamic (MHD) equilibria in a fixed toroidal domain using a Fourier expansion for the inverse coordinates (R,Z) representing nested magnetic surfaces. A set of nonlinear coupled ordinary differential equations for the spectral coefficients of (R,Z) is solved using an accelerated steepest descent method. A stream function lambda is introduced to improve the mode convergence properties of the Fourier series for R and Z. Constraint equations relating the m greater than or equal to 2 moments of R and Z are solved to define a unique poloidal angle.
Harmonic analysis tools for stochastic magnetohydrodynamics equations in Besov spaces
NASA Astrophysics Data System (ADS)
Sango, Mamadou; Tegegn, Tesfalem Abate
2016-08-01
We establish a regularity result for stochastic heat equations in probabilistic evolution spaces of Besov type and we use it to prove a global in time existence and uniqueness of solution to a stochastic magnetohydrodynamics equation. The existence result holds with a positive probability which can be made arbitrarily close to one. The work is carried out by blending harmonic analysis tools such as Littlewood-Paley decomposition, Jean-Micheal Bony paradifferential calculus and stochastic calculus. The law of large numbers is a key tool in our investigation. Our global existence result is new in three-dimensional spaces.
Mitochondrial DNA deletion percentage in sun exposed and non sun exposed skin.
Powers, Julia M; Murphy, Gillian; Ralph, Nikki; O'Gorman, Susan M; Murphy, James E J
2016-12-01
The percentages of mitochondrial genomes carrying the mtDNA(3895) and the mtDNA(4977) (common) deletion were quantified in sun exposed and non sun exposed skin biopsies, for five cohorts of patients varying either in sun exposure profile, age or skin cancer status. Non-melanoma skin cancer diagnoses are rising in Ireland and worldwide [12] but most risk prediction is based on subjective visual estimations of sun exposure history. A quantitative objective test for pre-neoplastic markers may result in better adherence to sun protective behaviours. Mitochondrial DNA (mtDNA) is known to be subject to the loss of a significant proportion of specific sections of genetic code due to exposure to ultraviolet light in sunlight. Although one such deletion has been deemed more sensitive, another, called the mtDNA(4977) or common deletion, has proved to be a more useful indicator of possible risk in this study. Quantitative molecular analysis was carried out to determine the percentage of genomes carrying the deletion using non sun exposed and sun exposed skin biopsies in cohorts of patients with high or low sun exposure profiles and two high exposure groups undergoing treatment for NMSC. Results indicate that mtDNA deletions correlate to sun exposure; in groups with high sun exposure habits a significant increase in deletion number in exposed over non sun exposed skin occurred. An increase in deletion percentage was also seen in older cohorts compared to the younger group. The mtDNA(3895) deletion was detected in small amounts in exposed skin of many patients, the mtDNA(4977) common deletion, although present to some extent in non sun exposed skin, is suggested to be the more reliable and easily detected marker. In all cohorts except the younger group with relatively lower sun exposure, the mtDNA(4977) deletion was more frequent in sun exposed skin samples compared to non-sun exposed skin.
Vibration Based Sun Gear Damage Detection
NASA Technical Reports Server (NTRS)
Hood, Adrian; LaBerge, Kelsen; Lewicki, David; Pines, Darryll
2013-01-01
Seeded fault experiments were conducted on the planetary stage of an OH-58C helicopter transmission. Two vibration based methods are discussed that isolate the dynamics of the sun gear from that of the planet gears, bearings, input spiral bevel stage, and other components in and around the gearbox. Three damaged sun gears: two spalled and one cracked, serve as the focus of this current work. A non-sequential vibration separation algorithm was developed and the resulting signals analyzed. The second method uses only the time synchronously averaged data but takes advantage of the signal/source mapping required for vibration separation. Both algorithms were successful in identifying the spall damage. Sun gear damage was confirmed by the presence of sun mesh groups. The sun tooth crack condition was inconclusive.
Signature extension for sun angle, volume 1
NASA Technical Reports Server (NTRS)
Smith, J. A. (Principal Investigator); Berry, J. K.; Heimes, F.
1975-01-01
The author has identified the following significant results. Within a restricted zenith sun angle range of 35 - 50 degrees, it was empirically observed that canopy reflectance is mainly Lambertian. Reflectance changes with crop stage were simple shifts in scale in the sun angle range. It was noted that sun angle variations depend on canopy characteristics. Effects of the vegetative canopy were most pronounced at the larger solar zenith angles (20 %). The linear sun angle correction coefficients demonstrate a dependency on both crop stage (15-20 %) and crop type (10-20 %). The use of canopy reflectance modeling allowed for the generation of a simulated data set over an extremely broad envelope of sun angles.
Sun Safe Mode Controller Design for LADEE
NASA Technical Reports Server (NTRS)
Fusco, Jesse C.; Swei, Sean S. M.; Nakamura, Robert H.
2015-01-01
This paper presents the development of sun safe controllers which are designed to keep the spacecraft power positive and thermally balanced in the event an anomaly is detected. Employed by NASA's Lunar Atmosphere and Dust Environment Explorer (LADEE), the controllers utilize the measured sun vector and the spacecraft body rates for feedback control. To improve the accuracy of sun vector estimation, the least square minimization approach is applied to process the sensor data, which is proven to be effective and accurate. To validate the controllers, the LADEE spacecraft model engaging the sun safe mode was first simulated and then compared with the actual LADEE orbital fight data. The results demonstrated the applicability of the proposed sun safe controllers.
SDO Asks: What's The Sun Doing Now?
NASA Technical Reports Server (NTRS)
Pesnell, W. D.
2007-01-01
Solar observations have tended to emphasize events like flares and CMEs, and what leads to these events. The past decade has seen an increasing emphasis on understanding the entire Sun, from the nuclear reactions at the core to the development and loss of magnetic loops in the corona. The Solar Dynamics Observatory (SDO) will return synoptic data, taken at a regular cadence and covering the entire Sun. This means you can still study events, but can also move forward to producing a quantitative model of what the Sun is doing today. The science investigations of SDO will determine how the Sun's magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere and geospace as the solar wind, energetic particles, and variations in the solar irradiance. How SDO data will transform the study of the Sun and the affect on stellar astrophysics will be discussed.
Disseminating a sun safety program to zoological parks: the effects of tailoring.
Lewis, Elizabeth; Mayer, Joni A; Slymen, Donald; Belch, George; Engelberg, Moshe; Walker, Kristina; Kwon, Harry; Elder, John
2005-09-01
Previous research found that a sun safety program for visitors at 1 zoo increased sun safety behaviors. This randomized study compared the effects of tailored dissemination materials plus 2 brief follow-up phone calls (tailored group) versus generic materials (basic group) on implementation by other zoos of the previously evaluated sun safety program. Education directors of 126 zoos completed surveys several months following initial dissemination and 1 year later. During Summer 1, 40% of tailored group zoos and 24% of basic group zoos offered visitors at least 1 sun safety activity (odds ratio=2.2, 95% confidence interval=1.0-4.8). During Summer 2, these rates were 34% and 44%, respectively (ns). The pattern of findings suggests that tailoring had no incremental long-term impact and that the generic materials produced a good level of dissemination.
Meridional Circulation in the Sun
NASA Technical Reports Server (NTRS)
Duvall, T. L., Jr.; Hanasoge, S. M.
2008-01-01
Measuring the depth variation of the meridional flows is important for understanding the solar cycle, at least according to a number of dynamo models. While attempting to extend the early observations of Giles (1999; Ph. D. thesis, Stanford Univ.) of time-distance measurements of flow, we have stumbled upon some systematic errors that can affect these measurements: 1) the additional distance traveled by radiation coming from points away from disk center causes an apparent 'shrinking' Sun, that is an apparent flow towards the disk center, 2) in measurements away from the central longitude, the rotation signal can leak into meridional flow signals, and 3) in measurements of the north-south mean travel times along the equator, a spurious error of 6 sec travel time is seen. That the signal is spurious is confirmed by observing half the time with the image rotated 180 degrees. Although this is an effect with mean travel times and not differences, it still seems useful to understand it. Attempts to understand and overcome these systematic problems will be presented. Forward modeling has been done using ray theory to test the sensitivity of travel times to various models.
NASA Technical Reports Server (NTRS)
Bahcall, J. N.
1986-01-01
The amount of dark matter in the disk of the Galaxy at the solar position is determined by comparing the observed distributions of tracer stars with the predictions obtained from different assumptions of how the unseen matter is distributed. The major uncertainties, observational and theoretical, are estimated. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the sun is about 0.1 solar mass/cu pc; the corresponding column density is about 30 solar masses/cu pc. This, so far unseen, material must be in a disk with an exponential scale height of less than 0.7 kpc. All the existing observations are consistent with the unseen disk material being in the form of stars not massive enough to burn hydrogen. It is suggested that the unseen material that is required to hold up the rotation curves of galaxies and to satisfy the virial theorem for clusters of galaxies might also be in the form of low-mass stars.
NASA Technical Reports Server (NTRS)
2006-01-01
A spectacular field of Martian sand ripples separates NASA's Mars Exploration Rover Spirit from the slopes of 'Husband Hill.' It has been 200 Martian days, or sols, since the rover started a descent from the top of the peak to the rover's current position on 'Low Ridge.' Looking back to the north on sol 813 (April 17, 2006), Spirit acquired this blue-filter (436-nanometer) view with the right panoramic camera (Pancam) while the Sun was low in the sky late in the afternoon. Because of the low-angle lighting (sunlight is coming from the left), images like this provide superb views of subtle textures in the topography both near and far. Husband Hill, where the rover was perched late last summer, rises prominently just left of center in this view. A 150-meter wide (500 foot) field of curving sand ripples named 'El Dorado' lies at the base of Husband Hill.
By collecting photos like this at different times of day, when lighting comes from different directions, scientists can distinguish surface properties such as color and reflectivity from topography and roughness. By separating these components they can map more details of the geologic terrain, providing new clues about the geologic history of Gusev Crater.
Magnetohydrodynamic Power Generation in the Laboratory Simulated Martian Entry Plasma
NASA Technical Reports Server (NTRS)
Vuskovic, L.; Popovic, S.; Drake, J.; Moses, R. W.
2005-01-01
This paper addresses the magnetohydrodynamic (MHD) conversion of the energy released during the planetary entry phase of an interplanetary vehicle trajectory. The effect of MHD conversion is multi-fold. It reduces and redirects heat transferred to the vehicle, and regenerates the dissipated energy in reusable and transportable form. A vehicle on an interplanetary mission carries about 10,000 kWh of kinetic energy per ton of its mass. This energy is dissipated into heat during the planetary atmospheric entry phase. For instance, the kinetic energy of Mars Pathfinder was about 4220 kWh. Based on the loss in velocity, Mars Pathfinder lost about 92.5% of that energy during the plasma-sustaining entry phase that is approximately 3900 kWh. An ideal MHD generator, distributed over the probe surface of Mars Pathfinder could convert more than 2000 kWh of this energy loss into electrical energy, which correspond to more than 50% of the kinetic energy loss. That means that the heat transferred to the probe surface can be reduced by at least 50% if the converted energy is adequately stored, or re-radiated, or directly used. Therefore, MHD conversion could act not only as the power generating, but also as the cooling process. In this paper we describe results of preliminary experiments with light and microwave emitters powered by model magnetohydrodynamic generators and discuss method for direct use of converted energy.
The transverse field Richtmyer-Meshkov instability in magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Wheatley, V.; Samtaney, R.; Pullin, D. I.; Gehre, R. M.
2014-01-01
The magnetohydrodynamic Richtmyer-Meshkov instability is investigated for the case where the initial magnetic field is unperturbed and aligned with the mean interface location. For this initial condition, the magnetic field lines penetrate the perturbed density interface, forbidding a tangential velocity jump and therefore the presence of a vortex sheet. Through simulation, we find that the vorticity distribution present on the interface immediately after the shock acceleration breaks up into waves traveling parallel and anti-parallel to the magnetic field, which transport the vorticity. The interference of these waves as they propagate causes the perturbation amplitude of the interface to oscillate in time. This interface behavior is accurately predicted over a broad range of parameters by an incompressible linearized model derived presently by solving the corresponding impulse driven, linearized initial value problem. Our use of an equilibrium initial condition results in interface motion produced solely by the impulsive acceleration. Nonlinear compressible simulations are used to investigate the behavior of the transverse field magnetohydrodynamic Richtmyer-Meshkov instability, and the performance of the incompressible model, over a range of shock strengths, magnetic field strengths, perturbation amplitudes and Atwood numbers.
A hybrid numerical fluid dynamics code for resistive magnetohydrodynamics
Johnson, Jeffrey
2006-04-01
Spasmos is a computational fluid dynamics code that uses two numerical methods to solve the equations of resistive magnetohydrodynamic (MHD) flows in compressible, inviscid, conducting media[1]. The code is implemented as a set of libraries for the Python programming language[2]. It represents conducting and non-conducting gases and materials with uncomplicated (analytic) equations of state. It supports calculations in 1D, 2D, and 3D geometry, though only the 1D configuation has received significant testing to date. Because it uses the Python interpreter as a front end, users can easily write test programs to model systems with a variety of different numerical and physical parameters. Currently, the code includes 1D test programs for hydrodynamics (linear acoustic waves, the Sod weak shock[3], the Noh strong shock[4], the Sedov explosion[5], magnetic diffusion (decay of a magnetic pulse[6], a driven oscillatory "wine-cellar" problem[7], magnetic equilibrium), and magnetohydrodynamics (an advected magnetic pulse[8], linear MHD waves, a magnetized shock tube[9]). Spasmos current runs only in a serial configuration. In the future, it will use MPI for parallel computation.
Nuclear-electric magnetohydrodynamic propulsion for submarine. Master's thesis
Bednarczyk, A.A.
1989-05-01
The thesis analyzes the superconducting technology for a shipboard magnetohydrodynamic propulsion system. Based on the the principles of magnetohydrodynamics (MHD), the concept of open-water efficiency was used to optimize the preliminary design of the MHD thruster. After the baseline submarine hull modeled after the Los Angeles class submarine was selected, propulsive efficiency and the top speed for four variant MHD submarines were evaluated. The design criteria were set at a 100-MWt nuclear reactor power upper limit and a requirement of 30 knots for the top speed. This required advanced reactor plants and advanced energy conversion systems. The selection of High Temperature Gas Reactor (HTGR) and Liquid-Metal Fast Breeder Reactor (LMFBR) was based on the combined merits of safety, environmental impact, high source temperature and maximum-volume power density (KW/L). With the reactor outlet temperatures of 2000 K, direct-cycle energy conversion-systems gave the best results in terms of thermal efficiency and propulsion plant power density. Two energy conversion systems selected were closed-cycle gas turbine geared to a superconducting generator, and closed-cycle liquid-metal MHD generator. Based on submarine reliability and safety, the option of using an intermediate heat exchanger was also considered. Finally, non-nuclear support systems affected by the advanced power plant and MHD propulsion, stressing submarine safety, are proposed.
Brightness Changes in Sun-like Stars
NASA Technical Reports Server (NTRS)
Henry, Stephen M.; Henry, Gregory W.
1998-01-01
Does the Sun's energy output vary with time? Are observable climatic changes on the earth caused by changes in the Sun? Can we gain greater insight into this relation-ship by studying other stars with properties similar to the Sun's? In recent years, satellite observations have shown that the solar irradiance varies in phase with the 1 l-year sunspot cycle. The Sun is brighter by about O.l% at the peak of the sunspot cycle when solar magnetic activity is at its maximum. Over longer intervals, changes in the cart h's climate and solar magnetic activity seem to be correlated. We are using automatic photoelectric telescopes to measure brightness changes in a sample of 150 Sun-like stars. Lowell Observatory astronomers have also observed about 30 of these same stars with a manual telescope in a program that began 10 years before ours. Since these two data sets were acquired with different instruments and so have significant systematic differences, we developed software to combine them accurately and, therefore, extend our observational time coverage. We show sample results of brightness variations over 14 years in several Sun-like stars with different ages. Longitudinal studies like these, combined with cross-sectional studies of the larger sample of stars, may eventually allow us to infer with confidence the Sun's long-term brightness history and its impact on the earth's climate.
Sun-synchronous satellite orbit determination
NASA Astrophysics Data System (ADS)
Ma, Der-Ming; Zhai, Shen-You
2004-02-01
The linearized dynamic equations used for on-board orbit determination of Sun-synchronous satellite are derived. Sun-synchronous orbits are orbits with the secular rate of the right ascension of the ascending node equal to the right ascension rate of the mean sun. Therefore the orbit is no more a closed circle but a tight helix about the Earth. In the paper, instead of treating the orbit as a closed circle, the actual helix orbit is taken as nominal trajectory. The details of the linearized equations of motion for the satellite in the Sun-synchronous orbit are derived. The linearized equations are obtained by perturbing the Keplerian motion with the J2 correction and the effect of sun's attraction being neglected. Combined with the GPS navigation equations, the Kalman filter formulation is given. The particular application considered is the circular Sun-synchronous orbit with the altitude of 800 km and inclination of 98.6°. The numerical example simulated by MATLAB® shows that only the pseudo-range data used in the algorithm still gives acceptable results. Based on the simulation results, we can use the on-board GPS receivers' signal only as an alternative to determine the orbit of Sun-Synchronous satellite and therefore circumvents the need for extensive ground support.
Sun signs Valdez Principles; rejoining CMA
Kirschner, E.
1993-02-17
Four year after an investors' group developed the Valdez Principles in response to the Exxon oil spill, Sun Co. (Philadelphia) has become the first major corporation to sign on to the environmental commitment. Sun also says it plans to rejoin the Chemical Manufacturers Association (CMA) in light of new emphasis on its chemical business and to recommit to the Responsible Care program. Sun negotiated the commitment's working with the Coalition for Economically Responsible Economies (CERES; New York), which devised the code of conduct, now called the CERES Principles. It requries goals of reducing environmental impact, as well as annual environmental auditing and public reporting of results. Annual environmental reporting is coming,' says Sun chairman and CEO Robert H. Campbell. CERES' report provides credibility and accountability, he says. Sun's signing is the onset of a stampede,' says New York City Comptroller Elizabeth Holtzman, who advises on investment of the city's $47-billion pension funds. CERES says that between tens of' Fortune 500 companies have shown interest in a negotiated code. The 50 other signers are smaller companies. Du Pont says it is waiting to see Sun's agreement. Campbell says the commitment complements Sun's five-year-old program, which incorporates the American Petroleum Institute program and CMA's Responsible Care initiative. I don't think anything will change that the customer will notice,' he adds.
SunPy—Python for solar physics
NASA Astrophysics Data System (ADS)
SunPy Community; Mumford, Stuart J.; Christe, Steven; Pérez-Suárez, David; Ireland, Jack; Shih, Albert Y.; Inglis, Andrew R.; Liedtke, Simon; Hewett, Russell J.; Mayer, Florian; Hughitt, Keith; Freij, Nabil; Meszaros, Tomas; Bennett, Samuel M.; Malocha, Michael; Evans, John; Agrawal, Ankit; Leonard, Andrew J.; Robitaille, Thomas P.; Mampaey, Benjamin; Campos-Rozo, Jose Iván; Kirk, Michael S.
2015-01-01
This paper presents SunPy (version 0.5), a community-developed Python package for solar physics. Python, a free, cross-platform, general-purpose, high-level programming language, has seen widespread adoption among the scientific community, resulting in the availability of a large number of software packages, from numerical computation (NumPy, SciPy) and machine learning (scikit-learn) to visualization and plotting (matplotlib). SunPy is a data-analysis environment specializing in providing the software necessary to analyse solar and heliospheric data in Python. SunPy is open-source software (BSD licence) and has an open and transparent development workflow that anyone can contribute to. SunPy provides access to solar data through integration with the Virtual Solar Observatory (VSO), the Heliophysics Event Knowledgebase (HEK), and the HELiophysics Integrated Observatory (HELIO) webservices. It currently supports image data from major solar missions (e.g., SDO, SOHO, STEREO, and IRIS), time-series data from missions such as GOES, SDO/EVE, and PROBA2/LYRA, and radio spectra from e-Callisto and STEREO/SWAVES. We describe SunPy's functionality, provide examples of solar data analysis in SunPy, and show how Python-based solar data-analysis can leverage the many existing tools already available in Python. We discuss the future goals of the project and encourage interested users to become involved in the planning and development of SunPy.
[Latest evidence about longevity of Sun Simiao].
Song, Zhen-Min
2013-01-01
Recording in the preface of Binglishufu (written by Lu Zhaolin of the Tang Dynasty) was the only direct evidence about the longevity of Sun Simiao. It recorded 'Sun Simiao said since his birth in the Xinyou Year of the Kaihuang Period, he was 93 years old'. But there were disputes over the time of Xinyou Year-581 AD or 541 AD? It is easy to pick holes in both arguments and the whole research, so the conclusion is not reliable. Recordings in Biography of Sun Simiao, which said 'the governor of the Luozhou area marveled at Sun's intelligence and called him the saint child', are also fabricated. According to literature, 'in the 3(rd) year of the Xianqing Period, Sun Simiao was invited by the emperor and lived in the deserted house of the Boyang Princess. He was more than 90 years old and did not have any visual or hearing loss … he was good to give lectures at various schools like Zhuang and Lao … in the Zhou Xuan Emperor Period Sun was tired of royal affairs and chose to be a hermit in the Taibai Mountain' (Tanghuiyao, Datang Xinyu, Tanbinlu). Sun Simiao should have been born in 560 AD. This time conformed to the time of his other events. He was 20 when a hermit and was 99 when he was invited by the Emperor Gaozong in the 3(rd) year of Xianqing.
Interplanetary Studies: Propagation of Disturbances Between the Sun and the Magnetosphere
NASA Astrophysics Data System (ADS)
Dryer, Murray
1994-09-01
This review is concerned with the interplanetary ‘transmission line’ between the Sun and the Earth's magnetosphere. It starts with comments about coronal mass ejections (CMEs) that are associated with various forms of solar activities. It then continues with some of the current views about their continuation through the heliosphere to Earth and elsewhere. The evolution of energy, mass, and momentum transfer is of prime interest since the temporal/spatial/magnitude behavior of the interplanetary electric field and transient solar wind dynamic pressure is relevant to the magnetospheric response (the presence or absence of geomagnetic storms and substorms) at Earth. Energetec particle flux predictions are discussed in the context of solar activity (flares, prominence eruptions) at various positions on the solar disk relative to Earth's central meridian. A number of multi-dimensional magnetohydrodynamic (MHD) models, applied to the solar, near-Sun, and interplanetary portions of the ‘transmission line’, are discussed. These model simulations, necessary to advancing our understanding beyond the phenomenological or morphological stages, are directed to deceptively simple questions such as the following: can one-to-one associations be made between specific forms of solar activity and magnetosphere response?
NASA Astrophysics Data System (ADS)
Intriligator, D. S.; Sun, W.; Detman, T.; Miller, W. D.; Intriligator, J.; Dryer, M.; Webber, W.; Deehr, C.; Gloeckler, G.
2016-11-01
The Sun has been observed for many years to be a dynamic influence in the heliosphere, and as the Voyager missions have continued long after achieving their original goals of observing the major planets they have provided the first in situ observations of the effects of solar activity in the heliosheath (HS), and the nearest portions of the local Interstellar Medium (LISM). Comparing these observations with models provides key insights. We employ two three-dimensional (3D) time-dependent models that simulate the propagation of shocks, other specific features, and the background solar wind throughout the heliosphere, starting with the solar background and solar event boundary conditions near the Sun at 2.5 Rs. The Hybrid Heliospheric Modeling System with Pickup Protons (HHMS-PI) is a 3D time- dependent Magnetohydrodynamic (MHD) simulation. HAFSS (HAF Solar Surface) is a 3D time-dependent kinematic simulation. Comparing our models with the observations indicates that solar effects are seen in the heliosphere, the HS, and the LISM in in-situ spacecraft measurements of plasma, magnetic field, energetic particles, cosmic rays, and plasma waves. There is quantitative agreement (at ACE, Ulysses, VI, V2) with data (e.g., solar wind, IMF, Ulysses SWICS pickup protons (PUPs)). Propagating shocks are slowed due to PUPs. The 3D locations of solar events and of various spacecraft are key to understanding the 3D propagation and timing of shocks, other specific features, and gradients throughout the heliosphere, HS, and LISM.
MAGNETIZED JETS DRIVEN BY THE SUN: THE STRUCTURE OF THE HELIOSPHERE REVISITED
Opher, M.; Drake, J. F.; Zieger, B.; Gombosi, T. I.
2015-02-20
The classic accepted view of the heliosphere is a quiescent, comet-like shape aligned in the direction of the Sun’s travel through the interstellar medium (ISM) extending for thousands of astronomical units (AUs). Here, we show, based on magnetohydrodynamic (MHD) simulations, that the tension (hoop) force of the twisted magnetic field of the Sun confines the solar wind plasma beyond the termination shock and drives jets to the north and south very much like astrophysical jets. These jets are deflected into the tail region by the motion of the Sun through the ISM similar to bent galactic jets moving through the intergalactic medium. The interstellar wind blows the two jets into the tail but is not strong enough to force the lobes into a single comet-like tail, as happens to some astrophysical jets. Instead, the interstellar wind flows around the heliosphere and into the equatorial region between the two jets. As in some astrophysical jets that are kink unstable, we show here that the heliospheric jets are turbulent (due to large-scale MHD instabilities and reconnection) and strongly mix the solar wind with the ISM beyond 400 AU. The resulting turbulence has important implications for particle acceleration in the heliosphere. The two-lobe structure is consistent with the energetic neutral atom (ENA) images of the heliotail from IBEX where two lobes are visible in the north and south and the suggestion from the Cassini ENAs that the heliosphere is “tailless.”.
NASA Astrophysics Data System (ADS)
Giacobbe, F. W.; Giacobbe, M. J.
This paper describes a computational method of estimating physical and chemical properties within the solar interior without employing calculations involving opacities. Instead of using opacities to help determine how interior solar temperatures vary with the radial distance between the centre of the sun and its 'surface', an iterative technique employing empirical adiabatic 'cooling' and a fusion energy production rate expression were employed for this purpose. Other iterative calculations were also made (nearly simultaneously) to ensure that all known solar constraint conditions were precisely satisfied (except for the photospheric 'surface' temperature) during this computational process. In addition, all calculations could be performed using a conventional PC employing an Intel Pentium CPU and a computer program coded in ANSI C. Due to the simplifications that were possible using the techniques employed during this study, as well as the advantages associated with using a programming language that produces machine code when compiled, all solar structural details could be generated very rapidly using an ordinary computer. The results of this study were compared with more conventional results obtained by others. This comparison indicated that the methods employed within this paper produced interior intensive solar properties that were in reasonable agreement with similar properties obtained by employing more sophisticated computational approaches. Although it is not claimed that the results generated during this study are any better than more conventionally obtained findings, it is thought that these results, as well as our computational methods, are interesting and potentially useful to others. In particular, it is thought that the techniques outlined in this paper may provide a useful introduction to more complicated techniques of solar modelling.
Anisotropic microstructure near the sun
NASA Astrophysics Data System (ADS)
Coles, W. A.; Grall, R. R.; Spangler, S. R.; Sakurai, T.; Harmon, J. K.
1996-07-01
Radio scattering observations provide a means of measuring a two-dimensional projection of the three-dimensional spatial spectrum of electron density, i.e., in the plane perpendicular to the line of sight. Earlier observations have shown that the microstructure at scales of the order of 10 km becomes highly field-aligned inside of 10 Rsolar [Armstrong et al., 1990]. Earlier work has also shown that density fluctuations at scales larger than 1000 km have a Kolmogorov spectrum, whereas the smaller scale structure has a flatter spectrum and is considerably enhanced above the Kolmogorov ``background'' [Coles et al., 1991]. Here we present new observations made during 1990 and 1992. These confirm the earlier work, which was restricted to one source on a few days, but they suggest that the anisotropy changes abruptly near 6 Rsolar which was not clear in the earlier data. The axial ratio measurements are shown on Figure 1 below. The new observations were made with a more uniform sampling of the spatial plane. They show that contours of constant correlation are elliptical. This is apparently inconsistent with the spatial correlation of the ISEE-3 magnetic field which shows a ``Maltese Cross'' shape [Matthaeus et al., 1990]. However this inconsistency may be only apparent: the magnetic field and density correlations need not have the same shape; the scale of the magnetic field correlations is at least 4 orders of magnitude larger; they are much further from the sun; and they are point measurements whereas ours are path-integrated. We also made two simultaneous measurements, at 10 Rsolar, of the anisotropy on scales of 200 to 4000 km. Significant anisotropy was seen on the smaller scales, but the larger scale structure was essentially isotropic. This suggests that the process responsible for the anisotropic microstructure is independent of the larger scale isotropic turbulence. It is then tempting to speculate that the damping of this anisotropic process inside of 6 Rsolar
The Sun's dusty interstellar environment
NASA Astrophysics Data System (ADS)
Sterken, Veerle
2016-07-01
The Sun's dusty interstellar environment Interstellar dust from our immediate interstellar neighborhood travels through the solar system at speeds of ca. 26 km/s: the relative speed of the solar system with respect to the local interstellar cloud. On its way, its trajectories are altered by several forces like the solar radiation pressure force and Lorentz force. The latter is due to the charged dust particles that fly through the interplanetary magnetic field. These trajectories differ per particle type and size and lead to varying fluxes and directions of the flow inside of the solar system that depend on location but also on phase in the solar cycle. Hence, these fluxes and directions depend strongly on the configuration of the inner regions and outer regions of the heliosphere. Several missions have measured this dust in the solar system directly. The Ulysses dust detector data encompasses 16 years of intestellar dust fluxes and approximate directions, Stardust captured returned to Earth a few of these particles sucessfully, and finally the Cassini dust detector allowed for compositional information to be obtained from the impacts on the instrument. In this talk, we give an overview of the current status of interstellar dust research through the measurements made inside of the solar system, and we put them in perspective to the knowledge obtained from more classical astronomical means. In special, we focus on the interaction of the dust with the interplanetary magnetic field, and on what we learn about the dust (and the fields) by comparing the available dust data to computer simulations of dust trajectories. Finally, we synthesize the different methods of observation, their results, and give a preview on new research opportunities in the coming year(s).
Cool Stars, Stellar Systems and the Sun.
NASA Astrophysics Data System (ADS)
Stempels, Eric
2009-02-01
The series of 'Cool Star' meetings concentrates on the astrophysics of low-mass stars (with masses similar to that of the Sun and lower), including the Sun. The meeting in St. Andrews, Scotland, was the 15th in this series, and focused in particular on the origin of low-mass stars and their planets, as well as the properties of their atmospheres. This volume provides a comprehensive overview of the science presented by the 350 participants of this meeting. The book is suitable for researchers and graduate students interested in the astrophysics of cool stars and the Sun.
THE SUN AS A VARIABLE STAR III.
observations has taught us more about the variations of solar type stars than about the sun itself. The observations of 15 stars of spectral types F and...stars 40 Leo, beta CVn and eta Boo this deviation is less than 0.004 mag. No evidence of variability in the stars which are similar to the sun has been...detected during this program. If we assume the sun acts in similar fashion to each of these stars, its variability over a fifteen-year period probably
Hispanic-themed music and Salsa dance performances helped kick off the Johnson Space Center celebration of Hispanic Heritage Month, commemorating the histories, cultures and contributions of Hispan...
Developing Leadership in a Multitype Library Consortium: Ten Years of SEFLIN Sun Seekers
ERIC Educational Resources Information Center
Curry, Elizabeth A.; Smithee, Jeannette
2009-01-01
The Southeast Florida Library and Information Network (SEFLIN) has presented the Sun Seeker Leadership Institute biennially since 1997. SEFLIN, a multitype library consortium headquartered in Boca Raton, Florida, was one of the first groups to sponsor a library leadership institute held as a monthly series of events over the period of a year. One…
ULYSSES comes full circle, before revisiting the Sun's poles
NASA Astrophysics Data System (ADS)
1998-04-01
From its unique perspective, Ulysses has provided scientists with the very first all-round map of the heliosphere, the huge bubble in space filled by the Sun's wind. The Earth swims deep inside the heliosphere, and gusts and shocks in the solar wind can harm satellites, power supplies and ommunications. They may also affect our planet's weather. A better grasp of the solar weather in the heliosphere is therefore one of the major aims of ESA's science programme. In a project of international cooperation between ESA and NASA, Ulysses was launched towards Jupiter in October 1990 by the US space shuttle Discovery. Arriving in February 1992, Ulysses stole energy from the giant planet in a slingshot manoeuvre and was propelled back towards the Sun in an elongated orbit almost at right angles to the ecliptic plane, where the Earth and other planets circle the Sun. "This month Ulysses returns to the point in space where its out-of-ecliptic journey began, but Jupiter isn't there," explains Richard Marsden, ESA's project scientist for Ulysses. "Following its own inexorable path around the Sun, Jupiter is far away on the opposite side of the Solar System. So Ulysses' course will not be changed a second time. The spacecraft is now in effect a man-made comet, forever bound into a 6-year polar orbit around the Sun." Ulysses now starts its second orbit. It will travel over the poles of the Sun in 2000-2001 just as the count of dark sunspots is expected to reach a maximum. With its operational life extended for the Ulysses Solar Maximum Mission, the spacecraft will find the heliosphere much stormier than during its first orbit. Discoveries so far Like its mythical namesake, Ulysses has already had an eventful voyage of discovery. Its unique trajectory has provided the scientific teams with a new perspective, from far out in space and especially in the previously unknown regions of the heliosphere over the Sun's poles. Passing within 9.8 degrees of the polar axis, the highly
SDO Catches Surfer Waves on the Sun
Scientists have spotted the iconic surfer's wave rolling through the atmosphere of the sun. The waves hold clues as to how energy moves through that atmosphere, known as the corona, and may help ex...
SDO Catches Comet Streaking by Sun
The Solar Dynamics Observatory's AIA instrument captured the first ever image of a comet passing directly in front of the sun in the early morning of July 6, 2011 in 171 angstrom. The comet comes i...
Nilaja Sun's "No Child...": Reflections on Success
ERIC Educational Resources Information Center
Sun, Nilaja; Alexander, Phillip; Huldeen, Branden; Russell, Ron; Friedman, Melissa
2007-01-01
This article describes Nilaja Sun's groundbreaking one-woman show about a TA, her students, and her school, and includes interviews with the author/performer, an excerpt of the work, and a discussion of the organization behind it.
Portegies Zwart, Simon F.
2009-05-01
The anomalous chemical abundances and the structure of the Edgeworth-Kuiper belt observed in the solar system constrain the initial mass and radius of the star cluster in which the Sun was born to M {approx_equal} 500-3000M {sub sun} and R {approx_equal} 1-3 pc. When the cluster dissolved, the siblings of the Sun dispersed through the galaxy, but they remained on a similar orbit around the Galactic center. Today these stars hide among the field stars, but 10-60 of them are still present within a distance of {approx}100 pc. These siblings of the Sun can be identified by accurate measurements of their chemical abundances, positions, and their velocities. Finding even a few will strongly constrain the parameters of the parental star cluster and the location in the Galaxy where we were born.
Physics of the Sun and its Atmosphere
NASA Astrophysics Data System (ADS)
Dwivedi, B. N.; Narain, U.
ch. 1. Recent advances in solar physics / B. N. Dwivedi -- ch. 2. Overview of the Sun / S. S. Hasan -- ch. 3. Seismic view of the Sun / S. M. Chitre and B. N. Dwivedi -- ch. 4. Solar magnetism / P. Venkatakrishnan and S. Gosain -- ch. 5. Waves and oscillations in the solar atmosphere / R. Erdélyi -- ch. 6. VUV spectroscopy of solar plasma / A. Mohan -- ch. 7. Active region diagnostics / H. E. Mason and D. Tripathi -- ch. 8. Hall effect and ambipolar diffusion in the lower solar atmosphere / V. Krishan -- ch. 9. On solar coronal heating mechanisms / K. Pandey and U. Narain -- ch. 10. Coronal mass ejections (CMEs) and associated phenomena / N. Srivastava -- ch. 11. The radio Sun / P. K. Manoharan -- ch. 12. The solar wind / P. K. Manoharan -- ch. 13. The Sun-Earth system: our home in space / J. L. Lean.
SDO and Hinode Views of the Sun
IRIS will advance our understanding of how the enigmatic interface region on the sun powers its dynamic million-degree atmosphere called the corona. IRIS will join the Solar Dynamics Observatory (S...
Sun-pointing programs and their accuracy
Zimmerman, J.C.
1981-05-01
Several sun-pointing programs and their accuracy are described. FORTRAN program listings are given. Program descriptions are given for both Hewlett-Packard (HP-67) and Texas Instruments (TI-59) hand-held calculators.
The Sun: Source of the Earth's Energy
NASA Technical Reports Server (NTRS)
Thompson, Barbara J.; Fisher, Richard R. (Technical Monitor)
2001-01-01
The Sun is the primary source of the Earth's energy. However, due to the complexity in the way the energy affects Earth, the various solar sources of the energy, and the variation exhibited by the Sun it is difficult to understand and predict the Earth's response to solar drivers. In addition to visible light the radiant energy of the Sun can exhibit variation in nearly all wavelengths, which can vary over nearly all timescales. Depending on the wavelength of the incident radiation the light can deposit energy in a wide variety or locations and drive processes from below Earth's surface to interplanetary space. Other sources of energy impacting Earth include energetic particles, magnetic fields, and mass and flow variations in the solar wind. Many of these variable energetic processes cannot be coupled and recent results continue to demonstrate that the complex dynamics of the Sun can have a great range of measurable impacts on Earth.
This timelapse video shows a coronal hole, as captured in ultraviolet light by NASA's Solar Dynamics Observatory on Jan. 10, 2011. Coronal holes are areas of the sun's surface that are the source o...
Solar physics: Weather of the magnetic Sun
NASA Astrophysics Data System (ADS)
Mathis, Stéphane
2017-04-01
The Sun is a magnetically active rotating star. Simultaneous observations with the STEREO and SDO space missions reveal solar analogues of planetary Rossby waves that will help forecast space weather.
Encouraging sun safety for children and adolescents.
Boe, Kathy; Tillotson, Elizabeth A
2006-06-01
The rise in the number of cases of skin cancers, both melanomas and nonmelanomas, has prompted increased awareness and educational efforts to limit sun exposure. Because 80% of lifetime sun exposure occurs before the age of 18, educating parents and adolescents to incorporate sun-protective behaviors into daily routines is particularly important. Education of parents is essential to establishing healthy behavior patterns in children. Educational interventions are recommended that encourage the following: using sunscreen, wearing hats with wide brims and clothing that blocks or absorbs ultraviolet rays, using sunglasses that block ultraviolet radiation, and seeking shade. Continued efforts are important through adolescence to maintain the established behaviors. School nurses are in a position to affect the health education curriculum, as well as school policies that promote sun safety behaviors.
RBSP: Studying the Sun's Influence on Earth
Two wide rings of high-intensity particles encircle our planet's equator. Known as the Van Allen Radiation Belts, their behavior in response to the sun directly impacts life on Earth and in orbit. ...
Huge Filament Rises From Sun's Northern Hemisphere
On August 1, 2010 following a C3-class solar flare from sunspot 1092, an enormous magnetic filament stretching across the sun's northern hemisphere erupted. This 304 angstrom video shows that filam...
ERIC Educational Resources Information Center
Abel, Ernest L.; Kruger, Michael L.
2010-01-01
The authors examined the association between birth month and longevity for major league baseball players. Players born in the month of November had the greatest longevities whereas those born in June had the shortest life spans. These differences remained after controlling for covariates such as birth year, career length, age at debut, height, and…
Flexible Photovoltaics: Mission Power from the Sun
2009-11-01
UNCLASSIFIED Flexible Photovoltaics : Mission Power from the Sun NSRDEC Project Officer: Steven Tucker Senior Engineer, EE COMM 508-233-6962 DSN 256...NOV 2009 2. REPORT TYPE 3. DATES COVERED 00-00-2009 to 00-00-2009 4. TITLE AND SUBTITLE Flexible Photovoltaics : Mission Power from the Sun...Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 UNCLASSIFIED Flexible Photovoltaics – Why? Travel Lighter, Stay Longer! Known
Digital Sun Sensor Multi-Spot Operation
Rufino, Giancarlo; Grassi, Michele
2012-01-01
The operation and test of a multi-spot digital sun sensor for precise sun-line determination is described. The image forming system consists of an opaque mask with multiple pinhole apertures producing multiple, simultaneous, spot-like images of the sun on the focal plane. The sun-line precision can be improved by averaging multiple simultaneous measures. Nevertheless, the sensor operation on a wide field of view requires acquiring and processing images in which the number of sun spots and the related intensity level are largely variable. To this end, a reliable and robust image acquisition procedure based on a variable shutter time has been considered as well as a calibration function exploiting also the knowledge of the sun-spot array size. Main focus of the present paper is the experimental validation of the wide field of view operation of the sensor by using a sensor prototype and a laboratory test facility. Results demonstrate that it is possible to keep high measurement precision also for large off-boresight angles. PMID:23443388
SunPy: Solar Physics in Python
NASA Astrophysics Data System (ADS)
Ryan, Daniel; Christe, Steven; Mumford, Stuart; Perez Suarez, David; Ireland, Jack; Shih, Albert Y.; Inglis, Andrew; Liedtke, Simon; Hewett, Russel
2015-04-01
SunPy is a community-developed open-source software library for solar physics. It is written in Python, a free, cross-platform, general-purpose, high-level programming language which is being increasingly adopted throughout the scientific community as well as further afield. This has resulted in a wide array of software packages useful for scientific computing, from numerical computation (NumPy, SciPy, etc.), to machine learning (scifitlearn), to visualization and plotting (matplotlib). SunPy aims to provide required specialised software for analysing solar and heliospheric datasets in Python. The current version is 0.5 with 0.6 expected to be released later this year. SunPy provides solar data access through integration with the Virtual Solar Observatory (VSO), the Heliophysics Event Knowledgebase (HEK), and the HELiophysics Integrated Observatory (HELIO) webservices. It supports common data types from major solar missions such as images (SDO/AIA, STEREO, PROBA2/SWAP etc.), time series (GOES/XRS, SDO/EVE, PROBA2/LYRA), and radio spectra (e-Callisto, STEREO/WAVES). SunPy’s code base is publicly available through github.com and can be contributed to by anyone. In this poster we demonstrate SunPy’s functionality and future goals of the project. We also encourage interested users to become involved in further developing SunPy.
Sea-Water Magnetohydrodynamic Propulsion for Next-Generation Undersea Vehicles
1990-02-01
1961. 2 J. B. Friauf, "Electromagnetic Ship Propulsion ," J. of Amer. Soc. of Naval Engrs., Feb., 1961, pp 139-142. 3 0. M. Phillips, "The Prospects for...Magnetohydrodynamic Ship Propulsion ," J. of Ship Research, March, 1962, pp 43-51. 4 R. A. Doragh, "Magnetohydrodynamic Ship Propulsion using...Paper # 67-432. I A. P. Baranov, "Future of Magnetohydrodynamic Ship Propulsion ," Sudostroyeniye, No. 12, 1966, pp 3-6. 8 A. Iwata, Y. Saji and S. Sato
bhlight: GENERAL RELATIVISTIC RADIATION MAGNETOHYDRODYNAMICS WITH MONTE CARLO TRANSPORT
Ryan, B. R.; Gammie, C. F.; Dolence, J. C.
2015-07-01
We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.
Diagnostic development and support of MHD (magnetohydrodynamics) test facilities
Not Available
1989-07-01
Mississippi State University (MSU) is developing diagnostic instruments for Magnetohydrodynamics (MHD) power train data acquisition and for support of MHD component development test facilities. Microprocessor-controlled optical instruments, initially developed for HRSR support, are being refined, and new systems to measure temperatures and gas-seed-slag stream characteristics are being developed. To further data acquisition and analysis capabilities, the diagnostic systems are being interfaced with MHD Energy Center computers. Technical support for the diagnostic needs of the national MHD research effort is being provided. MSU personnel will also cooperate with government agencies and private industries to improve the transformation of research and development results into processes, products and services applicable to their needs.
Hamiltonian magnetohydrodynamics: Lagrangian, Eulerian, and dynamically accessible stability—Theory
Andreussi, T.; Morrison, P. J.; Pegoraro, F.
2013-09-15
Stability conditions of magnetized plasma flows are obtained by exploiting the Hamiltonian structure of the magnetohydrodynamics (MHD) equations and, in particular, by using three kinds of energy principles. First, the Lagrangian variable energy principle is described and sufficient stability conditions are presented. Next, plasma flows are described in terms of Eulerian variables and the noncanonical Hamiltonian formulation of MHD is exploited. For symmetric equilibria, the energy-Casimir principle is expanded to second order and sufficient conditions for stability to symmetric perturbation are obtained. Then, dynamically accessible variations, i.e., variations that explicitly preserve invariants of the system, are introduced and the respective energy principle is considered. General criteria for stability are obtained, along with comparisons between the three different approaches.
Characterization of Magnetohydrodynamic (MHD) Shock Sensor using Schlieren Imaging
NASA Astrophysics Data System (ADS)
Rockwell, Owen; Hargather, Michael
2013-11-01
Schlieren imaging is used to quantitatively determine the speed and pressure duration of a shock wave traveling through air. The high-speed quantitative schlieren images are then used to characterize a new magnetohydrodynamic (MHD) shock sensor. This device uses the air density and particle velocity changes across a shock wave to determine the shock velocity via the distortion of a magnetic field. Using Faraday's law of electromagnetic induction, the shock velocity and pressure can be interpreted from a change in potential across the electrodes within the device. This principle along with the assumption that the shock wave is traveling through the undisturbed air allows for the calculation of shock velocity. Piezoelectric pressure gauges are used for comparison to measure the pressure pulse magnitude and duration.
Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence
Squire, J.; Bhattacharjee, A.
2015-11-02
Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is nomore » strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.« less
Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence
Squire, J.; Bhattacharjee, A.
2015-11-02
Here, this article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of alpha effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of alpha, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.
High-beta turbulence in two-dimensional magnetohydrodynamics
NASA Technical Reports Server (NTRS)
Fyfe, D.; Montgomery, D.
1975-01-01
Incompressible turbulent flows were investigated in the framework of ideal magnetohydrodynamics. Equilibrium canonical distributions are determined in a phase whose coordinates are the real and imaginary parts of the Fourier coefficients for the field variables. The magnetic field and fluid velocity have variable x and y components, and all field quantities are independent of z. Three constants of the motion are found which survive the truncation in Fourier space and permit the construction of canonical distributions with three independent temperatures. Spectral densities are calculated. One of the more novel physical effects is the appearance of macroscopic structures involving long wavelength, self-generated, magnetic fields ("magnetic islands"). In the presence of finite dissipation, energy cascades to higher wave numbers can be accompanied by vector potential cascades to lower wave numbers, in much the same way that in the fluid dynamic case, energy cascades to lower wave numbers accompany entropy cascades to higher wave numbers.
Hamiltonian and action formalisms for two-dimensional gyroviscous magnetohydrodynamics
Morrison, P. J. Lingam, M.; Acevedo, R.
2014-08-15
A general procedure for constructing action principles for continuum models via a generalization of Hamilton's principle of mechanics is described. Through the procedure, an action principle for a gyroviscous magnetohydrodynamics model is constructed. The model is shown to agree with a reduced version of Braginskii's fluid equations. The construction reveals the origin of the gyromap, a device used to derive previous gyrofluid models. Also, a systematic reduction procedure is presented for obtaining the Hamiltonian structure in terms of the noncanonical Poisson bracket. The construction procedure yields a class of Casimir invariants, which are then used to construct variational principles for equilibrium equations with flow and gyroviscosity. The procedure for obtaining reduced fluid models with gyroviscosity is also described.
Development of magnetohydrodynamic modes during sawteeth in tokamak plasmas
Firpo, M.-C.; Ettoumi, W.; Farengo, R.; Ferrari, H. E.; García-Martínez, P. L.; Lifschitz, A. F.
2013-07-15
A dynamical analysis applied to a reduced resistive magnetohydrodynamics model is shown to explain the chronology of the nonlinear destabilization of modes observed in tokamak sawteeth. A special emphasis is put on the nonlinear self-consistent perturbation of the axisymmetric m = n = 0 mode that manifests through the q-profile evolution. For the very low fusion-relevant resistivity values, the q-profile is shown to remain almost unchanged on the early nonlinear timescale within the central tokamak region, which supports a partial reconnection scenario. Within the resistive region, indications for a local flattening or even a local reversed-shear of the q-profile are given. The impact of this ingredient in the occurrence of the sawtooth crash is discussed.
MAGNETOHYDRODYNAMIC SIMULATION OF A SIGMOID ERUPTION OF ACTIVE REGION 11283
Jiang Chaowei; Feng Xueshang; Wu, S. T.; Hu Qiang E-mail: fengx@spaceweather.ac.cn E-mail: qh0001@uah.edu
2013-07-10
Current magnetohydrodynamic (MHD) simulations of the initiation of solar eruptions are still commonly carried out with idealized magnetic field models, whereas the realistic coronal field prior to eruptions can possibly be reconstructed from the observable photospheric field. Using a nonlinear force-free field extrapolation prior to a sigmoid eruption in AR 11283 as the initial condition in an MHD model, we successfully simulate the realistic initiation process of the eruption event, as is confirmed by a remarkable resemblance to the SDO/AIA observations. Analysis of the pre-eruption field reveals that the envelope flux of the sigmoidal core contains a coronal null and furthermore the flux rope is prone to a torus instability. Observations suggest that reconnection at the null cuts overlying tethers and likely triggers the torus instability of the flux rope, which results in the eruption. This kind of simulation demonstrates the capability of modeling the realistic solar eruptions to provide the initiation process.
Magnetohydrodynamic disc winds and line width distributions - II
NASA Astrophysics Data System (ADS)
Chajet, L. S.; Hall, P. B.
2017-02-01
We study AGN emission line profiles combining an improved version of the accretion disc-wind model of Murray & Chiang with the magnetohydrodynamic (MHD) model of Emmering et al. Here, we extend our previous work to consider central objects with different masses and/or luminosities. We have compared the dispersions in our model C IV line-width distributions to observational upper limit on that dispersion, considering both smooth and clumpy torus models. Following Fine et al., we transform that scatter in the profile line-widths into a constraint on the torus geometry and show how the half-opening angle of the obscuring structure depends on the mass of the central object and the accretion rate. We find that the results depend only mildly on the dimensionless angular momentum, one of the two integrals of motion that characterize the dynamics of the self-similar ideal MHD outflows.
Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics
Adams, Mark F.; Samtaney, Ravi; Brandt, Achi
2010-09-01
Multigrid methods can solve some classes of elliptic and parabolic equations to accuracy below the truncation error with a work-cost equivalent to a few residual calculations – so-called ‘‘textbook” multigrid efficiency. We investigate methods to solve the system of equations that arise in time dependent magnetohydrodynamics (MHD) simulations with textbook multigrid efficiency. We apply multigrid techniques such as geometric interpolation, full approximate storage, Gauss–Seidel smoothers, and defect correction for fully implicit, nonlinear, second-order finite volume discretizations of MHD. We apply these methods to a standard resistive MHD benchmark problem, the GEM reconnection problem, and add a strong magnetic guide field,more » which is a critical characteristic of magnetically confined fusion plasmas. We show that our multigrid methods can achieve near textbook efficiency on fully implicit resistive MHD simulations.« less
Monolithic multigrid methods for two-dimensional resistive magnetohydrodynamics
Adler, James H.; Benson, Thomas R.; Cyr, Eric C.; MacLachlan, Scott P.; Tuminaro, Raymond S.
2016-01-06
Magnetohydrodynamic (MHD) representations are used to model a wide range of plasma physics applications and are characterized by a nonlinear system of partial differential equations that strongly couples a charged fluid with the evolution of electromagnetic fields. The resulting linear systems that arise from discretization and linearization of the nonlinear problem are generally difficult to solve. In this paper, we investigate multigrid preconditioners for this system. We consider two well-known multigrid relaxation methods for incompressible fluid dynamics: Braess--Sarazin relaxation and Vanka relaxation. We first extend these to the context of steady-state one-fluid viscoresistive MHD. Then we compare the two relaxation procedures within a multigrid-preconditioned GMRES method employed within Newton's method. To isolate the effects of the different relaxation methods, we use structured grids, inf-sup stable finite elements, and geometric interpolation. Furthermore, we present convergence and timing results for a two-dimensional, steady-state test problem.
Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics
Adams, Mark F.; Samtaney, Ravi; Brandt, Achi
2013-12-14
Multigrid methods can solve some classes of elliptic and parabolic equations to accuracy below the truncation error with a work-cost equivalent to a few residual calculations – so-called “textbook” multigrid efficiency. We investigate methods to solve the system of equations that arise in time dependent magnetohydrodynamics (MHD) simulations with textbook multigrid efficiency. We apply multigrid techniques such as geometric interpolation, full approximate storage, Gauss-Seidel smoothers, and defect correction for fully implicit, nonlinear, second-order finite volume discretizations of MHD. We apply these methods to a standard resistive MHD benchmark problem, the GEM reconnection problem, and add a strong magnetic guide field, which is a critical characteristic of magnetically confined fusion plasmas. We show that our multigrid methods can achieve near textbook efficiency on fully implicit resistive MHD simulations.
Temporal intermittency of energy dissipation in magnetohydrodynamic turbulence.
Zhdankin, Vladimir; Uzdensky, Dmitri A; Boldyrev, Stanislav
2015-02-13
Energy dissipation in magnetohydrodynamic (MHD) turbulence is known to be highly intermittent in space, being concentrated in sheetlike coherent structures. Much less is known about intermittency in time, another fundamental aspect of turbulence which has great importance for observations of solar flares and other space or astrophysical phenomena. In this Letter, we investigate the temporal intermittency of energy dissipation in numerical simulations of MHD turbulence. We consider four-dimensional spatiotemporal structures, "flare events," responsible for a large fraction of the energy dissipation. We find that although the flare events are often highly complex, they exhibit robust power-law distributions and scaling relations. We find that the probability distribution of dissipated energy has a power-law index close to α≈1.75, similar to observations of solar flares, indicating that intense dissipative events dominate the heating of the system. We also discuss the temporal asymmetry of flare events as a signature of the turbulent cascade.
Magnetohydrodynamic actuation of droplets for millimetric planar fluidic systems
Ahmadi, A. McDermid, C. M.; Markley, L.
2016-01-04
In this work, a magnetohydrodynamic method is proposed for the actuation of droplets in small-scale planar fluidic systems, providing an alternative to commonly used methods such as electrowetting-on-dielectric. Elementary droplet-based operations, including transport, merging, and mixing, are demonstrated. The forces acting on millimetric droplets are carefully investigated, with a primary focus on the magnetic actuation force and on the unbalanced capillary forces that arise due to hysteresis. A super-hydrophobic channel is 3D printed to guide the droplets, with thin wires installed as contact electrodes and permanent magnets providing a static magnetic field. It is shown that droplet motion is enhanced by increasing the droplet size and minimizing the electrode contact surface. The effects of channel geometry on threshold voltage and minimum moveable droplet volume are characterized. Finally, the presence of electrolysis is investigated and mitigating strategies are discussed.
Three-dimensional force-free looplike magnetohydrodynamic equilibria
NASA Technical Reports Server (NTRS)
Finn, John M.; Guzdar, Parvez N.; Usikov, Daniel
1994-01-01
Computations of three-dimensional force-free magnetohydrodynamic (MHD) equilibria, del x B = lambdaB with lambda = lambda(sub 0), a constant are presented. These equilibria are determined by boundary conditions on a surface corresponding to the solar photosphere. The specific boundary conditions used correspond to looplike magnetic fields in the corona. It is found that as lambda(sub 0) is increased, the loops of flux become kinked, and for sufficiently large lambda(sub 0), develop knots. The relationship between the kinking and knotting properties of these equilibria and the presence of a kink instability and related loss of equilibrium is explored. Clearly, magnetic reconnection must be involved for an unknotted loop equilibrium to become knotted, and speculations are made about the creation of a closed hyperbolic field line (X-line) about which this reconnection creating knotted field lines is centered.
Observation of a nonaxisymmetric magnetohydrodynamic self-organized state
Cothran, C. D.; Brown, M. R.; Gray, T.; Schaffer, M. J.; Marklin, G.; Lukin, V. S.
2010-05-15
A nonaxisymmetric stable magnetohydrodynamic (MHD) equilibrium within a prolate cylindrical conducting boundary has been produced experimentally at Swarthmore Spheromak Experiment (SSX) [M. R. Brown et al., Phys. Plasmas 6, 1717 (1999)]. It has m=1 toroidal symmetry, helical distortion, and flat lambda profile. Each of these observed characteristics are in agreement with the magnetically relaxed minimum magnetic energy Taylor state. The Taylor state is computed using the methods described by A. Bondeson et al. [Phys. Fluids 24, 1682 (1981)] and by J. M. Finn et al. [Phys. Fluids 24, 1336 (1981)] and is compared in detail to the measured internal magnetic structure. The lifetime of this nonaxisymmetric compact torus (CT) is comparable to or greater than that of the axisymmetric CTs produced at SSX; thus suggesting confinement is not degraded by its nonaxisymmetry. For both one- and two-spheromak initial state plasmas, this same equilibrium consistently emerges as the final state.
Lagrangian Frequency Spectrum as a Diagnostic for Magnetohydrodynamic Turbulence Dynamics
Busse, Angela; Mueller, Wolf-Christian; Gogoberidze, Grigol
2010-12-03
For the phenomenological description of magnetohydrodynamic turbulence competing models exist, e.g., Boldyrev [Phys. Rev. Lett. 96, 115002 (2006)] and Gogoberidze [Phys. Plasmas 14, 022304 (2007)], which predict the same Eulerian inertial-range scaling of the turbulent energy spectrum although they employ fundamentally different basic interaction mechanisms. A relation is found that links the Lagrangian frequency spectrum with the autocorrelation time scale of the turbulent fluctuations {tau}{sub ac} and the associated cascade time scale {tau}{sub cas}. Thus, the Lagrangian energy spectrum can serve to identify weak ({tau}{sub ac}<<{tau}{sub cas}) and strong ({tau}{sub ac{approx}{tau}cas}) interaction mechanisms providing insight into the turbulent energy cascade. The new approach is illustrated by results from direct numerical simulations of two- and three-dimensional incompressible MHD turbulence.
Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics
Adams, Mark F.; Samtaney, Ravi; Brandt, Achi
2010-09-01
Multigrid methods can solve some classes of elliptic and parabolic equations to accuracy below the truncation error with a work-cost equivalent to a few residual calculations - so-called 'textbook' multigrid efficiency. We investigate methods to solve the system of equations that arise in time dependent magnetohydrodynamics (MHD) simulations with textbook multigrid efficiency. We apply multigrid techniques such as geometric interpolation, full approximate storage, Gauss-Seidel smoothers, and defect correction for fully implicit, nonlinear, second-order finite volume discretizations of MHD. We apply these methods to a standard resistive MHD benchmark problem, the GEM reconnection problem, and add a strong magnetic guide field, which is a critical characteristic of magnetically confined fusion plasmas. We show that our multigrid methods can achieve near textbook efficiency on fully implicit resistive MHD simulations.
Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics
Adams, Mark F.; Samtaney, Ravi; Brandt, Achi
2010-09-01
Multigrid methods can solve some classes of elliptic and parabolic equations to accuracy below the truncation error with a work-cost equivalent to a few residual calculations – so-called ‘‘textbook” multigrid efficiency. We investigate methods to solve the system of equations that arise in time dependent magnetohydrodynamics (MHD) simulations with textbook multigrid efficiency. We apply multigrid techniques such as geometric interpolation, full approximate storage, Gauss–Seidel smoothers, and defect correction for fully implicit, nonlinear, second-order finite volume discretizations of MHD. We apply these methods to a standard resistive MHD benchmark problem, the GEM reconnection problem, and add a strong magnetic guide field, which is a critical characteristic of magnetically confined fusion plasmas. We show that our multigrid methods can achieve near textbook efficiency on fully implicit resistive MHD simulations.
Implicit Methods for the Magnetohydrodynamic Description of Magnetically Confined Plasmas
Jardin, S C
2010-09-28
Implicit algorithms are essential for predicting the slow growth and saturation of global instabilities in today’s magnetically confined fusion plasma experiments. Present day algorithms for obtaining implicit solutions to the magnetohydrodynamic (MHD) equations for highly magnetized plasma have their roots in algorithms used in the 1960s and 1970s. However, today’s computers and modern linear and non-linear solver techniques make practical much more comprehensive implicit algorithms than were previously possible. Combining these advanced implicit algorithms with highly accurate spatial representations of the vector fields describing the plasma flow and magnetic fields and with improved methods of calculating anisotropic thermal conduction now makes possible simulations of fusion experiments using realistic values of plasma parameters and actual configuration geometry.
A Liquid Metal Flume for Free Surface Magnetohydrodynamic Experiments
Nornberg, M.D.; Ji, H.; Peterson, J.L.; Rhoads, J.R.
2008-08-27
We present an experiment designed to study magnetohydrodynamic effects in free-surface channel flow. The wide aspect ratio channel (the width to height ratio is about 15) is completely enclosed in an inert atmosphere to prevent oxidization of the liquid metal. A custom-designed pump reduces entrainment of oxygen, which was found to be a problem with standard centrifugal and gear pumps. Laser Doppler Velocimetry experiments characterize velocity profiles of the flow. Various flow constraints mitigate secondary circulation and end effects on the flow. Measurements of the wave propagation characteristics in the liquid metal demonstrate the surfactant effect of surface oxides and the damping of fluctuations by a cross-channel magnetic field.
Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence.
Squire, J; Bhattacharjee, A
2015-11-01
This article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of α effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of α, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.
Hamiltonian and action formalisms for two-dimensional gyroviscous magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Morrison, P. J.; Lingam, M.; Acevedo, R.
2014-08-01
A general procedure for constructing action principles for continuum models via a generalization of Hamilton's principle of mechanics is described. Through the procedure, an action principle for a gyroviscous magnetohydrodynamics model is constructed. The model is shown to agree with a reduced version of Braginskii's fluid equations. The construction reveals the origin of the gyromap, a device used to derive previous gyrofluid models. Also, a systematic reduction procedure is presented for obtaining the Hamiltonian structure in terms of the noncanonical Poisson bracket. The construction procedure yields a class of Casimir invariants, which are then used to construct variational principles for equilibrium equations with flow and gyroviscosity. The procedure for obtaining reduced fluid models with gyroviscosity is also described.
Correspondence between constrained transport and vector potential methods for magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Mocz, Philip
2017-01-01
We show that one can formulate second-order field- and flux-interpolated constrained transport/central difference (CT/CD) type methods as cell-centered magnetic vector potential schemes. We introduce four vector potential CTA/CDA schemes - three of which correspond to CT/CD methods of Tóth (2000) [1] and one of which is a new simple flux-CT-like scheme - where the centroidal vector potential is the primal update variable. These algorithms conserve a discretization of the ∇ ṡ B = 0 condition to machine precision and may be combined with shock-capturing Godunov type base schemes for magnetohydrodynamics. Recasting CT in terms of a centroidal vector potential allows for some simple generalizations of divergence-preserving methods to unstructured meshes, and potentially new directions to generalize CT schemes to higher-order.
WOMBAT: A Scalable and High-performance Astrophysical Magnetohydrodynamics Code
NASA Astrophysics Data System (ADS)
Mendygral, P. J.; Radcliffe, N.; Kandalla, K.; Porter, D.; O’Neill, B. J.; Nolting, C.; Edmon, P.; Donnert, J. M. F.; Jones, T. W.
2017-02-01
We present a new code for astrophysical magnetohydrodynamics specifically designed and optimized for high performance and scaling on modern and future supercomputers. We describe a novel hybrid OpenMP/MPI programming model that emerged from a collaboration between Cray, Inc. and the University of Minnesota. This design utilizes MPI-RMA optimized for thread scaling, which allows the code to run extremely efficiently at very high thread counts ideal for the latest generation of multi-core and many-core architectures. Such performance characteristics are needed in the era of “exascale” computing. We describe and demonstrate our high-performance design in detail with the intent that it may be used as a model for other, future astrophysical codes intended for applications demanding exceptional performance.
Inverse cascade of magnetic helicity in magnetohydrodynamic turbulence.
Müller, Wolf-Christian; Malapaka, Shiva Kumar; Busse, Angela
2012-01-01
The nonlinear dynamics of magnetic helicity HM, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media, is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high-resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of HM is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. 77, 321 (1976)]. By revisiting this theory, a universal dynamical balance relation is found that includes the effects of kinetic helicity as well as kinetic and magnetic energies on the inverse cascade of HM and explains the above-mentioned discrepancy. Consideration of the result in the context of mean-field dynamo theory suggests a nonlinear modification of the α-dynamo effect, which is important in the context of magnetic-field excitation in turbulent plasmas.
NON-LOCALITY OF HYDRODYNAMIC AND MAGNETOHYDRODYNAMIC TURBULENCE
Cho, Jungyeon
2010-12-20
We compare non-locality of interactions between different scales in hydrodynamic (HD) turbulence and magnetohydrodynamic (MHD) turbulence in a strongly magnetized medium. We use three-dimensional incompressible direct numerical simulations to evaluate non-locality of interactions. Our results show that non-locality in MHD turbulence is much more pronounced than that in HD turbulence. Roughly speaking, non-local interactions count for more than 10% of total interactions in our MHD simulation on a grid of 512{sup 3} points. However, there is no evidence that non-local interactions are important in our HD simulation with the same numerical resolution. We briefly discuss how non-locality affects the energy spectrum.
Two-and-a-half-dimensional magnetohydrodynamic turbulence
NASA Technical Reports Server (NTRS)
Montgomery, D.; Turner, L.
1982-01-01
The homogeneous turbulence for which fluctuating magnetic fields and velocity fields are independent of one spatial coordinate but still possess all three components are studied to form a generalized two-and-half dimensional geometry. The integral of the z-vector potential and the magnetic helicity are shown to be ideal invariants, and the basic dynamical variables and the equations of uniform-density incompressible magnetohydrodynamics are defined. The possibility of simultaneous inverse cascades is considered, and Kolmogoroff dimensional analysis is employed to infer omnidirectional inverse cascade spectra. Implications of a selective decay hypothesis, where a tendency exists in the initial value problem for the ideal invariants directly cascaded to higher wavenumbers to be selectively dissipated, and the possibility of a dynamo action in the considered geometry, are examined.
Once more: The continuous spectrum of ideal magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Goedbloed, J. P.
1998-09-01
A controversy on the existence of continuous spectra of ideal magnetohydrodynamics in addition to the well-known Alfvén and slow continua, dating back to a conjecture by Grad [Proc. Natl. Acad. Sci. USA 70, 3377 (1973)] and revived by Lashmore-Davies, Thyagaraja, and Cairns [Phys. Plasmas 4, 3243 (1997)], is once more resolved by demonstrating that the resolvent operator is bounded in the relevant domain: There are no additional continua. In addition, the solution of the initial value problem is constructed in terms of the three-dimensional Green's dyadic, which is free of apparent singularities and clearly exhibits the classical continua as δ functions on the diagonal. This construction provides the connection with the proper and improper normal modes and shows that the local dynamics on the magnetic surfaces is described by the classical continua.
An axisymmetric magnetohydrodynamic model for the Crab pulsar wind bubble
NASA Technical Reports Server (NTRS)
Begelman, Mitchell C.; Li, Zhi-Yun
1992-01-01
We extend Kennel and Coroniti's (1984) spherical magnetohydrodynamic models for the Crab Nebula to include the pinching effect of the toroidal magnetic field. Since the bulk nebular flow is likely to be very submagnetosonic, a quasi-static treatment is possible. We show that the pinching effect can be responsible for the observed elongation of the pulsar wind bubble, as indicated by the surface brightness contours of optical synchrotron radiation. From the observed elongation we estimate a value for sigma, the ratio of Poynting flux to plasma kinetic energy flux in the free pulsar wind, which is consistent with previous results from spherical models. Using the inferred magnetic field configuration inside the pulsar wind bubble, combined with the observed dimensions of the X-ray nebula, we are able to constrain the particle distribution function. We conclude that, for a power-law injection function, the maximum energy has to be much larger in the pulsar equatorial region than in the polar region.
Magnetohydrodynamic Modeling of Solar System Processes on Geodesic Grids
NASA Astrophysics Data System (ADS)
Florinski, V.; Guo, X.; Balsara, D. S.; Meyer, C.
2013-04-01
This report describes a new magnetohydrodynamic numerical model based on a hexagonal spherical geodesic grid. The model is designed to simulate astrophysical flows of partially ionized plasmas around a central compact object, such as a star or a planet with a magnetic field. The geodesic grid, produced by a recursive subdivision of a base platonic solid (an icosahedron), is free from control volume singularities inherent in spherical polar grids. Multiple populations of plasma and neutral particles, coupled via charge-exchange interactions, can be simulated simultaneously with this model. Our numerical scheme uses piecewise linear reconstruction on a surface of a sphere in a local two-dimensional "Cartesian" frame. The code employs Haarten-Lax-van-Leer-type approximate Riemann solvers and includes facilities to control the divergence of the magnetic field and maintain pressure positivity. Several test solutions are discussed, including a problem of an interaction between the solar wind and the local interstellar medium, and a simulation of Earth's magnetosphere.
Scaling of Compressible Magnetohydrodynamic Turbulence in the Fast Solar Wind
NASA Astrophysics Data System (ADS)
Banerjee, S.; Hadid, L. Z.; Sahraoui, F.; Galtier, S.
2016-10-01
The role of compressible fluctuations in the energy cascade of fast solar wind turbulence is studied using a reduced form of an exact law derived recently for compressible isothermal magnetohydrodynamics and in situ observations from the THEMIS B/ARTEMIS P1 spacecraft. A statistical survey of the data revealed a turbulent energy cascade over a range of two decades of scales that is broader than the previous estimates made from an exact incompressible law. A term-by-term analysis of the compressible model reveals new insight into the role played by the compressible fluctuations in the energy cascade. The compressible fluctuations are shown to amplify by two to four times the turbulent cascade rate with respect to the incompressible model in ∼ 10 % of the analyzed samples. This new estimated cascade rate is shown to provide the adequate energy dissipation required to account for the local heating of the non-adiabatic solar wind.
Three-Dimensional Numerical Modeling of Magnetohydrodynamic Augmented Propulsion Experiment
NASA Technical Reports Server (NTRS)
Turner, M. W.; Hawk, C. W.; Litchford, R. J.
2009-01-01
Over the past several years, NASA Marshall Space Flight Center has engaged in the design and development of an experimental research facility to investigate the use of diagonalized crossed-field magnetohydrodynamic (MHD) accelerators as a possible thrust augmentation device for thermal propulsion systems. In support of this effort, a three-dimensional numerical MHD model has been developed for the purpose of analyzing and optimizing accelerator performance and to aid in understanding critical underlying physical processes and nonideal effects. This Technical Memorandum fully summarizes model development efforts and presents the results of pretest performance optimization analyses. These results indicate that the MHD accelerator should utilize a 45deg diagonalization angle with the applied current evenly distributed over the first five inlet electrode pairs. When powered at 100 A, this configuration is expected to yield a 50% global efficiency with an 80% increase in axial velocity and a 50% increase in centerline total pressure.
Viscous, resistive magnetohydrodynamic stability computed by spectral techniques
Dahlburg, R. B.; Zang, T. A.; Montgomery, D.; Hussaini, M. Y.
1983-01-01
Expansions in Chebyshev polynomials are used to study the linear stability of one-dimensional magnetohydrodynamic quasiequilibria, in the presence of finite resistivity and viscosity. The method is modeled on the one used by Orszag in accurate computation of solutions of the Orr-Sommerfeld equation. Two Reynolds-like numbers involving Alfvén speeds, length scales, kinematic viscosity, and magnetic diffusivity govern the stability boundaries, which are determined by the geometric mean of the two Reynolds-like numbers. Marginal stability curves, growth rates versus Reynolds-like numbers, and growth rates versus parallel wave numbers are exhibited. A numerical result that appears general is that instability has been found to be associated with inflection points in the current profile, though no general analytical proof has emerged. It is possible that nonlinear subcritical three-dimensional instabilities may exist, similar to those in Poiseuille and Couette flow. PMID:16593375
Variational formulation for weakly nonlinear perturbations of ideal magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Hirota, M.
2011-10-01
A new equation of motion that governs weakly nonlinear phenomena in ideal magnetohydrodynamics (MHDs) is derived as a natural extension of the well-known linearized equation of motion for the displacement field. This derivation is made possible by expanding the MHD Lagrangian explicitly up to third order with respect to the displacement of plasma, which necessitates an efficient use of the Lie series expansion. The resultant equation of motion (i.e. the Euler-Lagrange equation) includes a new quadratic force term which is responsible for various mode-mode coupling due to the MHD nonlinearity. The third-order potential energy serves to quantify the coupling coefficient among resonant three modes and its cubic symmetry proves the Manley-Rowe relations. In contrast to earlier works, the coupling coefficient is expressed only by the displacement vector field, which is already familiar in the linear MHD theory, and both the fixed and free boundary cases are treated systematically.
Perpendicular diffusion of energetic particles in noisy reduced magnetohydrodynamic turbulence
Shalchi, A.; Hussein, M. E-mail: m_hussein@physics.umanitoba.ca
2014-10-10
A model for noisy reduced magnetohydrodynamic turbulence was recently proposed. This model was already used to study the random walk of magnetic field lines. In the current article we use the same model to investigate the diffusion of energetic particles across the mean magnetic field. To compute the perpendicular diffusion coefficient, two analytical theories are used, namely, the Non-Linear Guiding Center theory and the Unified Non-Linear Transport (UNLT) theory. It is shown that the two theories provide different results for the perpendicular diffusion coefficient. We also perform test-particle simulations for the aforementioned turbulence model. We show that only the UNLT theory describes perpendicular transport accurately, confirming that this is a powerful tool in diffusion theory.
Particle diffusion in strong field-guided magnetohydrodynamic turbulence
NASA Astrophysics Data System (ADS)
Tsang, Yue-Kin; Joanne Mason Collaboration
2015-11-01
We consider three-dimensional incompressible magnetohydrodynamic turbulence in the presence of a strong mean background magnetic field. We examine the Lagrangian statistics and characterize the transport properties of the system by numerically tracking a large number of passive massless particles. Previous studies demonstrated that in two dimensions, the presence of a weak background guiding field can suppress turbulent transport in the field-perpendicular direction. The situation in three dimensions is less clear. Here, we measure the single-particle diffusion along different directions with respect to the background magnetic field. By varying the background field strength, we quantify the effect of such guiding field on turbulent diffusion and interpret the results in terms of the Lagrangian velocity function. This work is supported by the UK EPSRC Grant EP/M004546/1.
MAGNETOHYDRODYNAMIC MODELING OF SOLAR SYSTEM PROCESSES ON GEODESIC GRIDS
Florinski, V.; Guo, X.; Balsara, D. S.; Meyer, C.
2013-04-01
This report describes a new magnetohydrodynamic numerical model based on a hexagonal spherical geodesic grid. The model is designed to simulate astrophysical flows of partially ionized plasmas around a central compact object, such as a star or a planet with a magnetic field. The geodesic grid, produced by a recursive subdivision of a base platonic solid (an icosahedron), is free from control volume singularities inherent in spherical polar grids. Multiple populations of plasma and neutral particles, coupled via charge-exchange interactions, can be simulated simultaneously with this model. Our numerical scheme uses piecewise linear reconstruction on a surface of a sphere in a local two-dimensional 'Cartesian' frame. The code employs Haarten-Lax-van-Leer-type approximate Riemann solvers and includes facilities to control the divergence of the magnetic field and maintain pressure positivity. Several test solutions are discussed, including a problem of an interaction between the solar wind and the local interstellar medium, and a simulation of Earth's magnetosphere.
Quantitative analytical model for magnetic reconnection in hall magnetohydrodynamics
Simakov, Andrei N
2008-01-01
Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths d{sub i} has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on d{sub i}.
Derivation of the Hall and Extended Magnetohydrodynamics Brackets
NASA Astrophysics Data System (ADS)
D'Avignon, Eric; Lingam, Manasvi; Morrison, Philip
2016-10-01
There are several plasma models intermediate in complexity between ideal magnetohydrodynamics (MHD) and two-fluid theory, with Hall and Extended MHD being two important examples. In this research we investigate several aspects of these theories, with the ultimate goal of deriving the noncanonical Poisson brackets used in their Hamiltonian formulations. We present fully Lagrangian actions for each, as opposed to the fully Eulerian, or mixed Eulerian-Lagrangian, actions that have appeared previously. As an important step in this process we exhibit each theory's two advected fluxes (in analogy to ideal MHD's advected magnetic flux), discovering also that with the correct choice of gauge they have corresponding Lie-dragged potentials resembling the electromagnetic vector potential, and associated conserved helicities. Finally, using the Euler-Lagrange map, we show how to derive the noncanonical Eulerian brackets from canonical Lagrangian ones.
Concomitant Hamiltonian and topological structures of extended magnetohydrodynamics
NASA Astrophysics Data System (ADS)
Lingam, Manasvi; Miloshevich, George; Morrison, Philip J.
2016-07-01
The paper describes the unique geometric properties of ideal magnetohydrodynamics (MHD), and demonstrates how such features are inherited by extended MHD, viz. models that incorporate two-fluid effects (the Hall term and electron inertia). The generalized helicities, and other geometric expressions for these models are presented in a topological context, emphasizing their universal facets. Some of the results presented include: the generalized Kelvin circulation theorems; the existence of two Lie-dragged 2-forms; and two concomitant helicities that can be studied via the Jones polynomial, which is widely utilized in Chern-Simons theory. The ensuing commonality is traced to the existence of an underlying Hamiltonian structure for all the extended MHD models, exemplified by the presence of a unique noncanonical Poisson bracket, and its associated energy.
bhlight: General Relativistic Radiation Magnetohydrodynamics with Monte Carlo Transport
Ryan, Benjamin R; Dolence, Joshua C.; Gammie, Charles F.
2015-06-25
We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and tomore » a slowly accreting Kerr black hole in axisymmetry.« less
bhlight: General Relativistic Radiation Magnetohydrodynamics with Monte Carlo Transport
Ryan, Benjamin R; Dolence, Joshua C.; Gammie, Charles F.
2015-06-25
We present bhlight, a numerical scheme for solving the equations of general relativistic radiation magnetohydrodynamics using a direct Monte Carlo solution of the frequency-dependent radiative transport equation. bhlight is designed to evolve black hole accretion flows at intermediate accretion rate, in the regime between the classical radiatively efficient disk and the radiatively inefficient accretion flow (RIAF), in which global radiative effects play a sub-dominant but non-negligible role in disk dynamics. We describe the governing equations, numerical method, idiosyncrasies of our implementation, and a suite of test and convergence results. We also describe example applications to radiative Bondi accretion and to a slowly accreting Kerr black hole in axisymmetry.
Theory of magnetohydrodynamic instabilities excited by energetic particles in tokamaks
Chen, L. )
1994-07-20
The resonant excitations of high-n magnetohydrodynamic (MHD) instabilities by the energetic ions/alpha particles in tokamaks are theoretically analyzed. Here, n is the toroidal mode number. Since, typically, the MHD modes consist of two-scale structures; one singular ( inertial'') region and one regular (ideal) region, the energetic particle contributions in the singular region are suppressed by the finite-size orbits. Analytical dispersion relations can then be derived via the asymptotic matching analysis. The dispersion relations have the generic form of the fishbone'' dispersion relation and demonstrate, in particular, the existence of two types of modes; that is, the MHD gap mode and the energetic-particle continuum mode. Specific expressions are given for both the kinetic ballooning modes (KBM) and the toroidal Alfven modes (TAM). It is suggested that the stability property may be qualitatively regarded as the hybrid'' of conventional MHD tokamaks and field reversed ion rings. [copyright]American Institute of Physics
NASA Astrophysics Data System (ADS)
Wu, S. T.; Wu, C.-C.; Liou, K.
2013-04-01
Before the discovery of EIT waves and coronal mass ejections (CMEs) it was already known that Moreton waves were observed to propagate across the solar disk during some solar flares. This magnetohydrodynamic wave was explained as the intersecting line between the edge of an expanding global coronal wavefront and the chromosphere (Uchida, 1968) where Uchida concluded that the Moreton wave was a fast mode MHD wave. In this presentation, we will show that the EIT wave could be a part of a CME induced wave propagating across the solar disk. To illustrate this scenario, we have employed a global 3D MHD model (Wu et al. 2001) to simulate this phenomenon for the May 12, 1997 event which was an Earth-directed CME observed by SOHO/EIT (Thompson et al. 1998). To carry out this simulation, the measured global magnetic fields obtained from the Stanford University Wilcox Solar Observatory (WSO) were used as the inputs to the simulation model. We were able to show that the scenario suggested by Uchida (1968), namely, the observed EIT wave propagating across the solar disk could be caused by the intersection line between the edge of an expanding CME induced wave front and the chromosphere. In addition to the flare source scenario, we concluded that an EIT (or EUV) wave can also be a part of a flare induced coronal wave with its foot print on the Sun's surface.
TURBULENT MAGNETOHYDRODYNAMIC RECONNECTION MEDIATED BY THE PLASMOID INSTABILITY
Huang, Yi-Min; Bhattacharjee, A.
2016-02-10
It has been established that the Sweet–Parker current layer in high Lundquist number reconnection is unstable to the super-Alfvénic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime where the Sweet–Parker current layer changes into a chain of plasmoids connected by secondary current sheets, and the averaged reconnection rate becomes nearly independent of the Lundquist number. In this work, a three-dimensional simulation with a guide field shows that the additional degree of freedom allows plasmoid instabilities to grow at oblique angles, which interact and lead to self-generated turbulent reconnection. The averaged reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfvén speed, which is similar to the two-dimensional result but is an order of magnitude lower than the fastest reconnection rate reported in recent studies of externally driven three-dimensional turbulent reconnection. Kinematic and magnetic energy fluctuations both form elongated eddies along the direction of the local magnetic field, which is a signature of anisotropic magnetohydrodynamic turbulence. Both energy fluctuations satisfy power-law spectra in the inertial range, where the magnetic energy spectral index is in the range from −2.3 to −2.1, while the kinetic energy spectral index is slightly steeper, in the range from −2.5 to −2.3. The anisotropy of turbulence eddies is found to be nearly scale-independent, in contrast with the prediction of the Goldreich–Sridhar theory for anisotropic turbulence in a homogeneous plasma permeated by a uniform magnetic field.
Bjorken flow in one-dimensional relativistic magnetohydrodynamics with magnetization
NASA Astrophysics Data System (ADS)
Pu, Shi; Roy, Victor; Rezzolla, Luciano; Rischke, Dirk H.
2016-04-01
We study the one-dimensional, longitudinally boost-invariant motion of an ideal fluid with infinite conductivity in the presence of a transverse magnetic field, i.e., in the ideal transverse magnetohydrodynamical limit. In an extension of our previous work Roy et al., [Phys. Lett. B 750, 45 (2015)], we consider the fluid to have a nonzero magnetization. First, we assume a constant magnetic susceptibility χm and consider an ultrarelativistic ideal gas equation of state. For a paramagnetic fluid (i.e., with χm>0 ), the decay of the energy density slows down since the fluid gains energy from the magnetic field. For a diamagnetic fluid (i.e., with χm<0 ), the energy density decays faster because it feeds energy into the magnetic field. Furthermore, when the magnetic field is taken to be external and to decay in proper time τ with a power law ˜τ-a, two distinct solutions can be found depending on the values of a and χm. Finally, we also solve the ideal magnetohydrodynamical equations for one-dimensional Bjorken flow with a temperature-dependent magnetic susceptibility and a realistic equation of state given by lattice-QCD data. We find that the temperature and energy density decay more slowly because of the nonvanishing magnetization. For values of the magnetic field typical for heavy-ion collisions, this effect is, however, rather small. It is only for magnetic fields about an order of magnitude larger than expected for heavy-ion collisions that the system is substantially reheated and the lifetime of the quark phase might be extended.
Turbulent Magnetohydrodynamic Reconnection Mediated by the Plasmoid Instability
NASA Astrophysics Data System (ADS)
Huang, Yi-Min; Bhattacharjee, A.
2016-02-01
It has been established that the Sweet-Parker current layer in high Lundquist number reconnection is unstable to the super-Alfvénic plasmoid instability. Past two-dimensional magnetohydrodynamic simulations have demonstrated that the plasmoid instability leads to a new regime where the Sweet-Parker current layer changes into a chain of plasmoids connected by secondary current sheets, and the averaged reconnection rate becomes nearly independent of the Lundquist number. In this work, a three-dimensional simulation with a guide field shows that the additional degree of freedom allows plasmoid instabilities to grow at oblique angles, which interact and lead to self-generated turbulent reconnection. The averaged reconnection rate in the self-generated turbulent state is of the order of a hundredth of the characteristic Alfvén speed, which is similar to the two-dimensional result but is an order of magnitude lower than the fastest reconnection rate reported in recent studies of externally driven three-dimensional turbulent reconnection. Kinematic and magnetic energy fluctuations both form elongated eddies along the direction of the local magnetic field, which is a signature of anisotropic magnetohydrodynamic turbulence. Both energy fluctuations satisfy power-law spectra in the inertial range, where the magnetic energy spectral index is in the range from -2.3 to -2.1, while the kinetic energy spectral index is slightly steeper, in the range from -2.5 to -2.3. The anisotropy of turbulence eddies is found to be nearly scale-independent, in contrast with the prediction of the Goldreich-Sridhar theory for anisotropic turbulence in a homogeneous plasma permeated by a uniform magnetic field.
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2015-10-01
On 7 November, 2012 at 08:00 UT, an enormous tornado of plasma rose from the surface of the Sun. It twisted around and around, climbing over the span of 10 hours to a height of 50 megameters roughly four times the diameter of the Earth! Eventually, this monster tornado became unstable and erupted violently as a coronal mass ejection (CME).Now, a team of researchers has analyzed this event in an effort to better understand the evolution of giant solar tornadoes like this one.Oscillating AxisIn this study, led by Irakli Mghebrishvili and Teimuraz Zaqarashvili of Ilia State University (Georgia), images taken by the Solar Dynamics Observatorys Atmospheric Imaging Assembly were used to track the tornados motion as it grew, along with a prominence, on the solar surface.The team found that as the tornado evolved, there were several intervals during which it moved back and forth quasi-periodically. The authors think these oscillations were due to one of two effects when the tornado was at a steady height: either twisted threads of the tornado were rotating around each other, or a magnetic effect known as kink waves caused the tornado to sway back and forth.Determining which effect was at work is an important subject of future research, because the structure and magnetic configuration of the tornado has implications for the next stage of this tornados evolution: eruption.Eruption from InstabilitySDO/AIA 3-channel composite image of the tornado an hour before it erupted in a CME. A coronal cavity has opened above the tornado; the top of the cavity is indicated by an arrow. [NASA/SDO/AIA; Mghebrishvili et al. 2015]Thirty hours after its formation, the tornado (and the solar prominence associated with it) erupted as a CME, releasing enormous amounts of energy. In the images from shortly before that moment, the authors observed a cavity open in the solar corona above the tornado. This cavity gradually expanded and rose above the solar limb until the tornado and prominence
Atmospheric Science Data Center
2014-07-09
... 06/30/1991 Temporal Resolution: Monthly average Tools: Contact User Services ... Water Radiative Forcing Shortwave Radiation Surface Temperature Order Data: Contact User Services: Order Data ...
2017-01-01
Highlights activities, events, and analyses associated with the natural gas industry. Volume and price data are presented each month for natural gas production, distribution, consumption, and interstate pipeline activities. Producer related activities and underground storage data are also reported.
Robinson, June K.; Guevara, Yanina; Gaber, Rikki; Clayman, Marla L.; Kwasny, Mary J.; Friedewald, John J.; Gordon, Elisa J.
2014-01-01
A culturally sensitive educational intervention that encouraged sun protection behaviors among kidney transplant recipients was developed and the short-term efficacy was evaluated. Non-Hispanic White, Hispanic/Latino, and non-Hispanic Black patients, who received a transplant 2–24 months prior to the study, were randomized into two study groups: intervention versus standard of care. Electronic reminders tailored to the weather conditions were sent every two weeks by text message or email. Self-reported surveys and biologic measurements were obtained prior to the intervention and six weeks later. Among the 101 study participants, there was a statistically significant increase in knowledge, recognition of personal risk of developing skin cancer, willingness to change sun protection behavior, and self-reported performance of sun protection in participants receiving the intervention in comparison with those receiving standard of care (p <0.05). The pigment darkening of the sun–exposed forearm and sun damage of the forearm and sunburns/ skin irritation from the sun were significantly less in participants receiving the intervention (p <0.05). Providing sun protection education at the beginning of summer with reminders tailored to weather conditions helped KTRs adopt sun protection practices. This sun protection program for KTRs may be incorporated into the care provided by the nephrologist or transplant surgeon. PMID:25395386
The Sol project: the sun in time
NASA Astrophysics Data System (ADS)
Pinho, L. G. F.; Porto de Mello, G. F.; de Medeiros, J. R.; Do Nascimento, J. D., Jr.; da Silva, L.
2003-08-01
The solar place in the set of stellar properties of the neighborhood, such as chemical composition, magnetic activity, lithium depletion, and others, suggests that the Sun may not exactly be a representative star. A few of the solar putative peculiarities seem to involve details of its evolutionary history, and that some light might be shed onto this question by a new approach based on the analysis of a time line in the HR diagram, searching for stars that might represent past, present and future solar evolutionary loci. The SOL Project (Solar Origin and Life) aims towards the identification, among the nearby stars, of those that share in detail the solar evolutionary track, in order to put the Sun as a star in proper perspective. We aim at obtaining, spectroscopically, atmospheric parameters, Fe and Li abundances, space velocities, state of evolution, degree of chromospheric activity and rotational velocities of a stellar sample, selected from precise astrometry and photometry of the Hipparcos catalogue, as to represent the Sun in various evolutionary stages along the solar mass, solar metallicity theoretical track: the early Sun, the present Sun, the subgiant Sun and the giant Sun. Here we present a progress report of the survey: the sample selection, OPD spectroscopic observations and preliminary results of the atmospheric parameters and evolutionary status analysis. As a by-product, we also present a new effective temperature calibration, based on published Infrared Flux Method data, and calibrated explicitly for precise spectroscopic stellar metallicities, for the (B-V), (BT-VT), (R-I), (V-I), (V-R) and (V-K) color indices, and valid for cool, normal and moderately metal-poor giant stars.
Lunar Reconnaissance Orbiter (LRO) Sun Safe Mode
NASA Technical Reports Server (NTRS)
Garrick, Joseph; Roger, J.
2010-01-01
The Lunar Reconnaissance Orbiter (LRO), a spacecraft designed and built at the National Aeronautics and Space Administration s (NASA) Goddard Space Flight Center (GSFC) in Greenbelt, MD, was launched on June 18, 2009 from Cape Canaveral. It is currently in orbit about the Moon taking detailed science measurements and providing a highly accurate mapping of the suface in preparation for the future return of astronauts to a permanent moon base. Onboard the spacecraft is a complex set of algorithms designed by the attitude control engineers at GSFC to control the pointig for all operational events, including anomalies that require the spacecraft to be put into a well known attitude configuration for a sufficiently long duration to allow for the investigation and correction of the anomaly. GSFC level requirements state that each spacecraft s control system design must include a configuration for this pointing and lso be able to maintain a thermally safe and power positive attitude. This stable control algorithm for anomalous events is commonly referred to as the safe mode and consists of control logic thatwill put the spacecraft in this safe configuration defined by the spacecraft s hardware, power and environment capabilities and limitations. The LRO Sun Safe mode consists of a coarse sun-pointing set of algorithms that puts the spacecraft into this thermally safe and power positive attitude and can be achieved wihin a required amount of time from any initial attitude, provided that the system momentum is within the momentum capability of the reaction wheels. On LRO the Sun Safe mode makes use of coarse sun sensors (CSS), an inertial reference unit (IRU) and reaction wheels (RW) to slew the spacecraft to a solar inertial pointing. The CSS and reaction wheels have some level of redundancy because of their numbers. However, the IRU is a single-point-failure piece of hardware. Without the rate information provided by the IRU, the Sun Safe control algorithms could not
7 CFR 3430.1008 - Sun Grant Information Analysis Center.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 15 2013-01-01 2013-01-01 false Sun Grant Information Analysis Center. 3430.1008...-GENERAL AWARD ADMINISTRATIVE PROVISIONS Sun Grant Program § 3430.1008 Sun Grant Information Analysis Center. The Centers and Subcenter shall maintain, at the North-Central Center, a Sun Grant...
7 CFR 3430.1008 - Sun Grant Information Analysis Center.
Code of Federal Regulations, 2011 CFR
2011-01-01
... 7 Agriculture 15 2011-01-01 2011-01-01 false Sun Grant Information Analysis Center. 3430.1008...-GENERAL AWARD ADMINISTRATIVE PROVISIONS Sun Grant Program § 3430.1008 Sun Grant Information Analysis Center. The Centers and Subcenter shall maintain, at the North-Central Center, a Sun Grant...
7 CFR 3430.1008 - Sun Grant Information Analysis Center.
Code of Federal Regulations, 2012 CFR
2012-01-01
... 7 Agriculture 15 2012-01-01 2012-01-01 false Sun Grant Information Analysis Center. 3430.1008...-GENERAL AWARD ADMINISTRATIVE PROVISIONS Sun Grant Program § 3430.1008 Sun Grant Information Analysis Center. The Centers and Subcenter shall maintain, at the North-Central Center, a Sun Grant...
7 CFR 3201.97 - Sun care products.
Code of Federal Regulations, 2013 CFR
2013-01-01
... 7 Agriculture 15 2013-01-01 2013-01-01 false Sun care products. 3201.97 Section 3201.97... Designated Items § 3201.97 Sun care products. (a) Definition. Products including sunscreens, sun blocks, and suntan lotions that are topical products that absorb or reflect the sun's ultraviolet radiation...
7 CFR 3201.97 - Sun care products.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 15 2014-01-01 2014-01-01 false Sun care products. 3201.97 Section 3201.97... Designated Items § 3201.97 Sun care products. (a) Definition. Products including sunscreens, sun blocks, and suntan lotions that are topical products that absorb or reflect the sun's ultraviolet radiation...
7 CFR 3430.1008 - Sun Grant Information Analysis Center.
Code of Federal Regulations, 2014 CFR
2014-01-01
... 7 Agriculture 15 2014-01-01 2014-01-01 false Sun Grant Information Analysis Center. 3430.1008...-GENERAL AWARD ADMINISTRATIVE PROVISIONS Sun Grant Program § 3430.1008 Sun Grant Information Analysis Center. The Centers and Subcenter shall maintain, at the North-Central Center, a Sun Grant...
Concurrent Psychosocial Predictors of Sun Safety among Middle School Youth
ERIC Educational Resources Information Center
Andreeva, Valentina A.; Reynolds, Kim D.; Buller, David B.; Chou, Chih-Ping; Yaroch, Amy L.
2008-01-01
Background: Sun-induced skin damage, which increases skin cancer risk, is initiated in early life and promoted through later sun exposure patterns. If sun safety determinants are well understood and addressed during the school years, skin cancer incidence might be reduced. This study tested psychosocial influences on youth's sun safety and…
The Solar Chimes: Searching for Oscillations inside the Sun.
ERIC Educational Resources Information Center
Wentzel, Donat G.
1991-01-01
The importance of investigating the sun's interior is discussed. One method for probing the interiors of some pulsating stars is described. The relationship between the sun's solar oscillation frequencies and the sun's solar cycles is discussed. A project to place six instruments around the world to observe the sun's oscillations (GONG) is…
Subgrid-scale modeling for the study of compressible magnetohydrodynamic turbulence in space plasmas
NASA Astrophysics Data System (ADS)
Chernyshov, A. A.; Karelsky, K. V.; Petrosyan, A. S.
2014-05-01
A state-of-the-art review is given of research by computing physics methods on compressible magnetohydrodynamic turbulence in space plasmas. The presence of magnetic fields and compressibility in this case makes space plasma turbulence much less amenable to direct numerical simulations than a neutral incompressible fluid. The large eddy simulation method is discussed, which was developed as an alternative to direct modeling and which filters the initial magnetohydrodynamic equations and uses the subgrid-scale modeling of universal small-scale turbulence. A detailed analysis is made of both the method itself and different subgrid-scale parametrizations for compressible magnetohydrodynamic turbulent flows in polytropic and heat-conducting plasmas. The application of subgrid-scale modeling to study turbulence in the local interstellar medium and the scale-invariant spectra of magnetohydrodynamic turbulence are discussed.
Stability of weak solutions to equations of magnetohydrodynamics with Lebesgue initial data
NASA Astrophysics Data System (ADS)
Fan, Jishan; Jiang, Song; Nakamura, Gen
We prove the existence, the uniqueness and the Lipschitz continuous dependence on the initial data of global weak solutions to equations of magnetohydrodynamics (MHD) with the initial data in the Lebesgue spaces.
NASA Technical Reports Server (NTRS)
Coffey, Brenman; Welch, Ray; Burt, Brad
2012-01-01
Satellite pointing is vital to the success of a mission. One element of that entails describing the position of the sun relative to the frame of the satellite. Coarse Sun Sensors (CSS) are typically used to provide the information to calculate the sun's position in Safe Modes or contingency operations. In the OCO-2 configuration there are 13 CSS total, which provide redundant 4 celestial coverage. Failures of the individual CSS elements can introduce holes in the celestial coverage resulting in potential loss of sun knowledge. These failures must be analyzed to determine if the contingency plan is sufficient to assure mission success. First the static case was looked at and determined that at a maximum, 3 CSS failures can be sustained on the body and 1 on the array without causing coverage holes. Also array sensors are more important to mission success. The Sun Vector calculation has been transcribed to MATLAB code and failure scenarios are being examined to determine the maximum error given a set of failure scenarios. This activity indicated that if there is a loss of the sun, the sun-searching algorithm could be modified to use XZ rotation as that is guaranteed to find it whereas the design using the YZ rotation misses the sun if it is at the + or - Y orientation.
The Sun Sense Study: An Intervention to Improve Sun Protection in Children
ERIC Educational Resources Information Center
Glasser, Alice; Shaheen, Magda; Glenn, Beth A.; Bastani, Roshan
2010-01-01
Objectives: To assess the effect of a multicomponent intervention on parental knowledge, sun avoidance behaviors, and sun protection practices in children 3-10 years. Methods: A randomized trial at a pediatric clinic recruited 197 caregiver-child pairs (90% parents). Intervention included a brief presentation and brochure for the parent and…
After the Bell: Developing Sun Sense--Learning about Protection from the Sun's Rays
ERIC Educational Resources Information Center
Farenga, Stephen J.; Ness, Daniel
2008-01-01
The American Academy of Dermatology (2008) reports that our students will experience 80% of their lifetime exposure to the Sun by the time they are 18. Further, research has demonstrated that continued exposure to the Sun's ultraviolet rays can lead to skin aging, sunburn, immune suppression, ocular melanoma, cataracts, corneal burns, and even…
Electron beam irradiation of sun-dried apricots for quality maintenance
NASA Astrophysics Data System (ADS)
Wei, Ming; Zhou, Linyan; Song, Hongbo; Yi, Jianyong; Wu, Bin; Li, Yaru; Zhang, Le; Che, Fengbin; Wang, Zhidong; Gao, Meixu; Li, Shurong
2014-04-01
The chemical, sensory, and microbial quality parameters of electron beam (EB)-irradiated and non-irradiated sun-dried apricots were periodically evaluated to optimize the EB irradiation of sun-dried apricots for quality maintenance. The sun-dried apricots were treated with 1.0, 2.0, 3.0, 4.0, and 5.0 kGy of EB and subsequently stored at ambient temperature. EB treatment at 1.0-3.0 kGy proved to be beneficial for retaining high levels of β-carotene, ascorbic acid, titratable acidity, total sugars, and color without any significant effect on sensory properties. Doses of 1.0-3.0 kGy retained the β-carotene content of sun-dried apricots to 8.21%, 9.27%, and 10.43% compared with 6.09% in control samples after 10 months of storage. After 10 months of storage, the maximum losses of ascorbic acid were 37.8% in control samples and 35.5% in 3.0 kGy-irradiated samples. Titratable acidity and total sugars were significantly enhanced immediately after 1.0-3.0 kGy irradiation treatment, and both parameters showed no significant change after 10 months of storage. Samples subjected to EB treatment at 3.0 kGy maintained a high overall acceptability of sun-dried apricots. Decreased number of viable microorganisms to below detection limits were observed after 3.0 kGy irradiation, and compared with the control, the logarithmic reductions after 10 months of storage were 0.98 for yeast and mold count, as well as 1.71 for bacterial count.
Federal Register 2010, 2011, 2012, 2013, 2014
2012-06-08
... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF TRANSPORTATION Office of the Secretary Application of Sun Air Express, LLC, d/b/a Sun Air International for Commuter... to show cause why it should not issue an order finding Sun Air Express, LLC d/b/a Sun...
The spectrum of darkonium in the Sun
Kouvaris, Chris; Langæble, Kasper; Nielsen, Niklas Grønlund
2016-10-10
Dark matter that gets captured in the Sun may form positronium-like bound states if it self-interacts via light dark photons. In this case, dark matter can either annihilate to dark photons or recombine in bound states which subsequently also decay to dark photons. The fraction of the dark photons that leave the Sun without decaying to Standard Model particles have a characteristic energy spectrum which is a mixture of the direct annihilation process, the decays of ortho- and para- bound states and the recombination process. The ultimate decay of these dark photons to positron-electron pairs (via kinetic mixing) outside the Sun creates a distinct signal that can either identify or set strict constraints on dark photon models.
Neptune as a Mirror for the Sun
NASA Astrophysics Data System (ADS)
Kohler, Susanna
2017-01-01
How would the Kepler mission see a star like the Sun? We now know the answer to this question due to a creative approach: a new study has used the Kepler K2 mission to detect signals from the Sun reflected off of the surface of Neptune.Asteroseismology uses different oscillation modes of a star to probe its internal structure and properties. [Tosaka]Information in OscillationsKeplers most glamorous work is in discovering new planets around other stars. To successfully do this, however, the spacecraft is also quietly doing a lot of very useful work in the background, characterizing the many stars in our vicinity that planets might be found around.One of the ways Kepler gets information about these stars is from oscillations of the stars intensities. In asteroseismology, we look at oscillatory modes that are caused by convection-driven pressure changes on the inside of the star. All stars with near-surface convection oscillate like this including the Sun and by measuring the oscillations in intensity of these stars, we can make inferences about the stars properties.A Planetary MirrorWe do this by first understanding our Suns oscillations especially well (made easier by the fact that its nearby!). Then we use asteroseimic scaling relations determined empirically that relate characteristics like mass and radius of other stars to those of the Sun, based on the relation between the stars oscillation properties to the Suns.The trouble is, those oscillation properties are difficult to measure, and different instruments often measure different values. For this reason, wed like to measure the Suns oscillations with the same instrument we use to measure other stars oscillations: Kepler.Top panel: Kepler K2 49-day light curve of Neptune. Bottom panel: power density spectrum as a function of frequency (grey). Neptunes rotation frequencies and harmonics appear toward the left side (blue); the excess power due to the solar modes is visible toward the bottom right. The green curve
The spectrum of darkonium in the Sun
NASA Astrophysics Data System (ADS)
Kouvaris, Chris; Langæble, Kasper; Grønlund Nielsen, Niklas
2016-10-01
Dark matter that gets captured in the Sun may form positronium-like bound states if it self-interacts via light dark photons. In this case, dark matter can either annihilate to dark photons or recombine in bound states which subsequently also decay to dark photons. The fraction of the dark photons that leave the Sun without decaying to Standard Model particles have a characteristic energy spectrum which is a mixture of the direct annihilation process, the decays of ortho- and para- bound states and the recombination process. The ultimate decay of these dark photons to positron-electron pairs (via kinetic mixing) outside the Sun creates a distinct signal that can either identify or set strict constraints on dark photon models.
NASA Technical Reports Server (NTRS)
Eddy, J. A.
1976-01-01
An investigation is conducted concerning the behavior of the sun during the last 7000 years. The C-14 content in carbonaceous fossil material can be used as an indicator regarding the level of solar activity at the time when the carbon was assimilated in the process of photosynthesis. Living trees, such as the bristlecone pine, provide a solar activity record to about 3000 B.C. The record can be extended with the aid of well-preserved dead wood to beyond 5000 B.C. The results of an analysis of solar activity levels as a function of time on the basis of C-14 contents are presented in a graph. Attention is given to the Maunder Minimum, a history of the sun in the last 5000 years, an interpretation of the major C-14 excursions, and the sun and climate history.
Role of clothes in sun protection.
Gambichler, Thilo; Altmeyer, Peter; Hoffmann, Klauss
2002-01-01
Ultraviolet (UV) radiation is the carcinogenic factor in sunlight. Damage to skin cells from repeated UV exposure can lead to the development of skin cancer. Apart from avoidance of the sun, the most frequently used form of UV protection has been the application of sunscreens. The use of textiles as a means of sun protection has been underrated in previous educational campaigns, even though suitable clothing offers usually simple and effective broadband protection against the sun. Apart from skin cancer formation, exacerbation of photosensitive disorders and premature skin aging could be prevented by suitable UV-protective clothing. Nevertheless, several studies have recently shown that, contrary to popular opinion, some textiles provide only limited UV protection. It has been found that one-third of commercial summer clothing items provide a UV protection factor (UPF) less than 15. Given the increasing interest in sun protection, recreationally and occupationally, test methods and a rating scheme for clothing were needed that would ensure sufficient UV protection. Various textile parameters have an influence on the UPF of a finished garment. Important parameters are the fabric porosity, type, color, weight and thickness. The application of UV absorbers into the yarns significantly improves the UPF of a garment. Under the conditions of wear and use several factors can alter the UV-protective properties of a textile, e.g., stretch, wetness and laundering. The use of UV-blocking cloths can provide excellent protection against the hazards of sunlight; this is especially true for garments manufactured as UV-protective clothing. However, further educational efforts are necessary to change people's sun behavior and raise awareness for the use of adequate sun-protective clothing.
Developmental milestones record - 6 months
Normal childhood growth milestones - 6 months; Childhood growth milestones - 6 months; Growth milestones for children - 6 months ... the weight on hands (often occurs by 4 months) Able to pick up a dropped object Able ...
Developmental milestones record - 12 months
Normal childhood growth milestones - 12 months; Growth milestones for children - 12 months; Childhood growth milestones - 12 months ... care provider. PHYSICAL AND MOTOR SKILLS A 12-month-old child is expected to: Be 3 times ...
Developmental milestones record - 18 months
Growth milestones for children - 18 months; Normal childhood growth milestones - 18 months; Childhood growth milestones - 18 months ... PHYSICAL AND MOTOR SKILL MARKERS The typical 18-month-old: Has a closed soft spot on the ...
Developmental milestones record - 4 months
Normal childhood growth milestones - 4 months; Childhood growth milestones - 4 months; Growth milestones for children - 4 months ... provider. PHYSICAL AND MOTOR SKILLS The typical 4-month-old baby should: Slow in weight gain to ...
Developmental milestones record - 9 months
Growth milestones for children - 9 months; Childhood growth milestones - 9 months; Normal childhood growth milestones - 9 months ... provider. PHYSICAL CHARACTERISTICS AND MOTOR SKILLS A 9-month-old has usually reached the following milestones: Gains ...
DOE Solar Energy Technologies Office
2015-04-01
The U.S. Department of Energy (DOE) SunShot Initiative is a collaborative national effort launched in 2011 that aggressively drives innovation to make solar energy fully cost competitive with traditional energy sources before the end of the decade. The SunShot fact sheet outlines goals and successes of the program as it works with private companies, universities, non-profit organizations, state and local governments, and national laboratories to drive down the cost of solar electricity to $0.06 per kilowatt-hour, without incentives, by the year 2020.
Shining Light through the Sun by Axions
Rashba, Timur
2007-11-27
I show that the Sun can become partially transparent to high energy photons in the presence of a pseudo-scalar. I discuss the possibilities of observing this effect. Present data are limited to the observation of the solar occultation of 3C 279 by EGRET in 1991; 98% C.L. detection of a non-zero flux of gamma rays passing through the Sun is not yet conclusive. Since the same occultation happens every October, future experiments, e.g. GLAST, are expected to have better sensitivity to the discussed effect.
The sun and heliosphere at solar maximum
NASA Technical Reports Server (NTRS)
Smith, E. J.; Marsden, R. G.; Balogh, A.; Gloeckler, G.; Geiss, J.; McComas, D. J.; McKibben, R. B.; MacDowall, R. J.; Lanzerotti, L. J.; Krupp, N.; Krueger, H.; Landgraf, M.
2003-01-01
Recent Ulysses observations from the Sun's equator to the poles reveal fundamental properties of the three-dimensional heliosphere at the maximum in solar activity. The heliospheric magnetic field originates from a magnetic dipole oriented nearly perpendicular to, instead of nearly parallel to, the Sun'rotation axis. Magnetic fields, solar wind, and energetic charged particles from low-latitude sources reach all latitudes, including the polar caps. The very fast high-latitude wind and polar coronal holes disappear and reappear together. Solar wind speed continues to be inversely correlated with coronal temperature. The cosmic ray flux is reduced symmetrically at all latitudes.
Ra: The Sun for Science and Humanity
NASA Technical Reports Server (NTRS)
1996-01-01
To guide the development of the Ra Strategic Framework, we defined scientific and applications objectives. For our primary areas of scientific interest, we choose the corona, the solar wind, the Sun's effect on the Earth, and solar theory and model development. For secondary areas of scientific interest, we selected sunspots, the solar constant, the Sun's gravitational field, helioseismology and the galactic cosmic rays. We stress the importance of stereoscopic imaging, observations at high spatial, spectral, and temporal resolutions, as well as of long duration measurements. Further exploration of the Sun's polar regions is also important, as shown already by the Ulysses mission. From an applications perspective, we adopted three broad objectives that would derive complementary inputs for the Strategic Framework. These were to identify and investigate: possible application spin-offs from science missions, possible solar-terrestrial missions dedicated to a particular application, and possible future applications that require technology development. The Sun can be viewed as both a source of resources and of threats. Our principal applications focus was that of threat mitigation, by examining ways to improve solar threat monitoring and early warning systems. We compared these objectives to the mission objectives of past, current, and planned international solar missions. Past missions (1962-1980) seem to have been focused on improvement of scientific knowledge, using multiple instrument spacecraft. A ten year gap followed this period, during which the results from previous missions were analyzed and solar study programmes were prepared in international organizations. Current missions (1990-1996) focus on particular topics such as the corona, solar flares, and coronal mass ejections. In planned missions, Sun/Earth interactions and environmental effects of solar activity are becoming more important. The corona is the centre of interest of almost all planned missions
Martian Moon Eclipses Sun, in Stages
NASA Technical Reports Server (NTRS)
2004-01-01
This panel illustrates the transit of the martian moon Phobos across the Sun. It is made up of images taken by the Mars Exploration Rover Opportunity on the morning of the 45th martian day, or sol, of its mission. This observation will help refine our knowledge of the orbit and position of Phobos. Other spacecraft may be able to take better images of Phobos using this new information. This event is similar to solar eclipses seen on Earth in which our Moon passes in front of the Sun. The images were taken by the rover's panoramic camera.
Haloes around the Moon and the Sun
NASA Astrophysics Data System (ADS)
Gaina, Alex; Gaina, Danielle A.
2008-10-01
The authors observations of the Haloes around the Moon and the Sun during few last years are reported. A Historical review of the phenomenon is given since the observations by Benvenuto Cellini and Gaston Tissandier is given. A photograph (from eight available) of the Halo around the Sun observed in Chisinau on 21 May 2007 is included. The Halo from 21 May 2007 occured after a very fast increasing of the air temperature during one day by more than 15 Deg. The authors consider, that the phenomenon is due to scattering of light on Cirri clouds(7 km altitude), present on the sky during that day. They formed due to very fast heating.
ERIC Educational Resources Information Center
Web Feet K-8, 2000
2000-01-01
This annotated subject guide to Web sites and additional resources focuses on Black History month. Specifies age levels for resources that include Web sites, CD-ROMs and software, videos, books, audios, magazines; includes professional resources; and presents a relevant class activity. (LRW)
Neff, Warren E
2010-12-07
These viewgraphs are to be provided to NNSA to update the status of the B61 Life Extension Project work and activities. The viewgraphs cover such issues as budget, schedule, scope, and the like. They are part of the monthly reporting process.