Science.gov

Sample records for including resistive mhd

  1. Magnetic reconnection in Hall-MHD including electron inertia

    NASA Astrophysics Data System (ADS)

    Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.

    2013-12-01

    Magnetic reconnection is an important energy conversion process in highly conducting plasmas, such as those present in the solar corona or in planetary magnetospheres. Within the framework of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. Within the more general framework of two-fluid MHD for a fully ionized hydrogen plasma, we retain the effects of the Hall current and electron inertia. We performed 2.5D Hall MHD simulations including electron inertia using a pseudo-spectral code which yields exact conservation (to round-off errors) of all the ideal invariants. We obtain finite reconnection rates even in the case of zero resistivity, thus showing the important influence of the electron inertia.

  2. Problems in nonlinear resistive MHD

    SciTech Connect

    Turnbull, A.D.; Strait, E.J.; La Haye, R.J.; Chu, M.S.; Miller, R.L.

    1998-12-31

    Two experimentally relevant problems can relatively easily be tackled by nonlinear MHD codes. Both problems require plasma rotation in addition to the nonlinear mode coupling and full geometry already incorporated into the codes, but no additional physics seems to be crucial. These problems discussed here are: (1) nonlinear coupling and interaction of multiple MHD modes near the B limit and (2) nonlinear coupling of the m/n = 1/1 sawtooth mode with higher n gongs and development of seed islands outside q = 1.

  3. Visco-Resistive MHD Modeling Benchmark of Forced Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Beidler, M. T.; Hegna, C. C.; Sovinec, C. R.; Callen, J. D.; Ferraro, N. M.

    2016-10-01

    The presence of externally-applied 3D magnetic fields can affect important phenomena in tokamaks, including mode locking, disruptions, and edge localized modes. External fields penetrate into the plasma and can lead to forced magnetic reconnection (FMR), and hence magnetic islands, on resonant surfaces if the local plasma rotation relative to the external field is slow. Preliminary visco-resistive MHD simulations of FMR in a slab geometry are consistent with theory. Specifically, linear simulations exhibit proper scaling of the penetrated field with resistivity, viscosity, and flow, and nonlinear simulations exhibit a bifurcation from a flow-screened to a field-penetrated, magnetic island state as the external field is increased, due to the 3D electromagnetic force. These results will be compared to simulations of FMR in a circular cross-section, cylindrical geometry by way of a benchmark between the NIMROD and M3D-C1 extended-MHD codes. Because neither this geometry nor the MHD model has the physics of poloidal flow damping, the theory of will be expanded to include poloidal flow effects. The resulting theory will be tested with linear and nonlinear simulations that vary the resistivity, viscosity, flow, and external field. Supported by OFES DoE Grants DE-FG02-92ER54139, DE-FG02-86ER53218, DE-AC02-09CH11466, and the SciDAC Center for Extended MHD Modeling.

  4. Kinetic effects of energetic particles on resistive MHD stability.

    PubMed

    Takahashi, R; Brennan, D P; Kim, C C

    2009-04-03

    We show that the kinetic effects of energetic particles can play a crucial role in the stability of the m/n=2/1 tearing mode in tokamaks (e.g., JET, JT-60U, and DIII-D), where the fraction of energetic particle beta(frac) is high. Using model equilibria based on DIII-D experimental reconstructions, the nonideal MHD linear stability of cases unstable to the 2/1 mode is investigated including a deltaf particle-in-cell model for the energetic particles coupled to the nonlinear 3D resistive MHD code NIMROD [C. C. Kim et al., Phys. Plasmas 15, 072507 (2008)10.1063/1.2949704]. It is observed that energetic particles have significant damping and stabilizing effects at experimentally relevant beta, beta(frac), and S, and excite a real frequency of the 2/1 mode. Extrapolation of the results is discussed for implications to JET and ITER, where the effects are projected to be significant.

  5. MHD modeling of magnetotail instability for localized resistivity

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim

    1994-01-01

    We present results of a three-dimensional magnetohydrodynamic (MHD) simulation of magnetotail evolution initiated by a sudden occurrence or increase of spatially localized resistivity as the major expected concequence of some localized microinstability. Because of the absence of a quantitative model, possible variations of resistivity levels with current density, or the reduction thereof, are not incorporated in the present investigation. The emphasis of the study is on an investigation of the changes to the overall evolution brought about by this localization, in particular, on the disruption and diversion of the cross-tail current and the nonlinear evolution of the magnetotail instability. The immediate consequences of the occurrence of the localized resistance and the resulting electric field are a reduction and diversion of the electric current around the region of high resistivity, associated with an increase of B(sub z) ('dipolarization') at the earthward edge and a decrease of B(sub z) at the tailward edge of this region. These effects, however, are localized and do not involve a reduction of the total cross-tail current and hence do not lead to the global development of a 'substorm current wedge,' which includes not only the reduction of the cross-tail current but also the buildup of a global field-aligned current system of 'regional 1' type (toward the Earth on the dawnside and away on the duskside of the tail). Such signatures develop at a later time, as consequences of a three-dimensional tearing instability, which is triggered by the occurrence of the resistivity. These features are found in combination with plasmoid formation and ejection, quite similar to results of earlier simulations with uniform resistivity. Differences are found in the timescale of the evolution, which tends to be shorter for localized resistivity, and in the propagation of the dipolarization effects in the equatorial plane. Whereas for uniform resistivity the temporal increase in

  6. Towards a Scalable Fully-Implicit Fully-coupled Resistive MHD Formulation with Stabilized FE Methods

    SciTech Connect

    Shadid, J N; Pawlowski, R P; Banks, J W; Chacon, L; Lin, P T; Tuminaro, R S

    2009-06-03

    This paper presents an initial study that is intended to explore the development of a scalable fully-implicit stabilized unstructured finite element (FE) capability for low-Mach-number resistive MHD. The discussion considers the development of the stabilized FE formulation and the underlying fully-coupled preconditioned Newton-Krylov nonlinear iterative solver. To enable robust, scalable and efficient solution of the large-scale sparse linear systems generated by the Newton linearization, fully-coupled algebraic multilevel preconditioners are employed. Verification results demonstrate the expected order-of-acuracy for the stabilized FE discretization of a 2D vector potential form for the steady and transient solution of the resistive MHD system. In addition, this study puts forth a set of challenging prototype problems that include the solution of an MHD Faraday conduction pump, a hydromagnetic Rayleigh-Bernard linear stability calculation, and a magnetic island coalescence problem. Initial results that explore the scaling of the solution methods are presented on up to 4096 processors for problems with up to 64M unknowns on a CrayXT3/4. Additionally, a large-scale proof-of-capability calculation for 1 billion unknowns for the MHD Faraday pump problem on 24,000 cores is presented.

  7. Flow stabilization of the ideal MHD resistive wall mode^1

    NASA Astrophysics Data System (ADS)

    Smith, S. P.; Jardin, S. C.; Freidberg, J. P.; Guazzotto, L.

    2009-05-01

    We demonstrate for the first time in a numerical calculation that for a typical circular cylindrical equilibrium, the ideal MHD resistive wall mode (RWM) can be completely stabilized by bulk equilibrium plasma flow, V, for a window of wall locations without introducing additional dissipation into the system. The stabilization is due to a resonance between the RWM and the Doppler shifted ideal MHD sound continuum. Our numerical approach introduces^2 u=φξ+ iV .∇ξ and the perturbed wall current^3 as variables, such that the eigenvalue, φ, only appears linearly in the linearized stability equations, which allows for the use of standard eigenvalue solvers. The wall current is related to the plasma displacement at the boundary by a Green's function. With the introduction of the resistive wall, we find that it is essential that the finite element grid be highly localized around the resonance radius where the parallel displacement, ξ, becomes singular. We present numerical convergence studies demonstrating that this singular behavior can be approached in a limiting sense. We also report on progress toward extending this calculation to an axisymmetric toroidal geometry. ^1Work supported by a DOE FES fellowship through ORISE and ORAU. ^2L.Guazzotto, J.P Freidberg, and R. Betti, Phys.Plasmas 15, 072503 (2008). ^3S.P. Smith and S. C. Jardin, Phys. Plasmas 15, 080701 (2008).

  8. A Gas-kinetic Scheme for the Two-Fluid MHD Equations with Resistivity

    NASA Astrophysics Data System (ADS)

    Anderson, Steven; Girimaji, Sharath; da Silva, Eduardo; Siebert, Diogo; Salazar, Juan

    2016-11-01

    The two-fluid MHD equations are a simplified model of plasma flow wherein a mixture of two species (electrons and ions) is considered. In this model, unlike single-fluid MHD, quasi-neutrality is not enforced, Ohm's Law is not used, and the fluids are not in thermal equilibrium - thus both fluids assume their own density, velocity, and temperature. Here we present a numerical scheme to solve the two-fluid MHD equations based on an extension of the gas-kinetic method. In contrast to previous implementations of the gas-kinetic scheme for MHD, the solution of the non-equilibrium distribution function for each gas at the cell interface is extended to include the effect of the electromagnetic forces as well as the inter-species collisions (resistivity). Closure of the fluid equations with the electromagnetic fields is obtained through Maxwell's equations, and physically correct divergences are enforced via correction potentials. Maxwell's equations are integrated via a simple Lax-Friedrichs type flux-splitting. To separate integration of the source and flux terms in the governing equations we use Strang splitting. Some numerical results are presented to demonstrate accuracy of the scheme and we discuss advantages and potential applications of the scheme. This research was supported by National Science Foundation Grant Number DGE-1252521 and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) of Brazil.

  9. Scalable implicit incompressible resistive MHD with stabilized FE and fully-coupled Newton–Krylov-AMG

    SciTech Connect

    Shadid, J. N.; Pawlowski, R. P.; Cyr, E. C.; Tuminaro, R. S.; Chacon, L.; Weber, P. D.

    2016-02-10

    Here, we discuss that the computational solution of the governing balance equations for mass, momentum, heat transfer and magnetic induction for resistive magnetohydrodynamics (MHD) systems can be extremely challenging. These difficulties arise from both the strong nonlinear, nonsymmetric coupling of fluid and electromagnetic phenomena, as well as the significant range of time- and length-scales that the interactions of these physical mechanisms produce. This paper explores the development of a scalable, fully-implicit stabilized unstructured finite element (FE) capability for 3D incompressible resistive MHD. The discussion considers the development of a stabilized FE formulation in context of the variational multiscale (VMS) method, and describes the scalable implicit time integration and direct-to-steady-state solution capability. The nonlinear solver strategy employs Newton–Krylov methods, which are preconditioned using fully-coupled algebraic multilevel preconditioners. These preconditioners are shown to enable a robust, scalable and efficient solution approach for the large-scale sparse linear systems generated by the Newton linearization. Verification results demonstrate the expected order-of-accuracy for the stabilized FE discretization. The approach is tested on a variety of prototype problems, that include MHD duct flows, an unstable hydromagnetic Kelvin–Helmholtz shear layer, and a 3D island coalescence problem used to model magnetic reconnection. Initial results that explore the scaling of the solution methods are also presented on up to 128K processors for problems with up to 1.8B unknowns on a CrayXK7.

  10. Role of Loss of Equilibrium and Magnetic Reconnection in Coronal Eruptions: Resistive and Hall MHD simulations

    NASA Astrophysics Data System (ADS)

    Yang, H.; Bhattacharjee, A.; Forbes, T. G.

    2008-12-01

    It has long been suggested that eruptive phenomena such as coronal mass ejections, prominence eruptions, and large flares might be caused by a loss of equilibrium in a coronal flux rope (Van Tend and Kuperus, 1978). Forbes et al. (1994) developed an analytical two-dimensional model in which eruptions occur due to a catastrophic loss of equilibrium and relaxation to a lower-energy state containing a thin current sheet. Magnetic reconnection then intervenes dynamically, leading to the release of magnetic energy and expulsion of a plasmoid. We have carried out high-Lundquist-number simulations to test the loss-of equilibrium mechanism, and demonstrated that it does indeed occur in the quasi-ideal limit. We have studied the subsequent dynamical evolution of the system in resistive and Hall MHD models for single as well as multiple arcades. The typical parallel electric fields are super-Dreicer, which makes it necessary to include collisionless effects via a generalized Ohm's law. It is shown that the nature of the local dissipation mechanism has a significant effect on the global geometry and dynamics of the magnetic configuration. The presence of Hall currents is shown to alter the length of the current sheet and the jets emerging from the reconnection site, directed towards the chromosphere. Furthermore, Hall MHD effects break certain symmetries of resistive MHD dynamics, and we explore their observational consequences.

  11. Performance analysis of the MHD-steam combined cycle, including the influence of cost

    SciTech Connect

    Berry, G. F.; Dennis, C. B.

    1980-08-01

    The MHD Systems group of the ANL Engineering Division is conducting overall system studies, utilizing the computer simulation code that has been developed at ANL. This analytical investigation is exploring a range of possible performance variables, in order to determine the sensitivity of a specific plant design to variation in key system parameters and, ultimately, to establish probable system performance limits. The comprehensive computer code that has been developed for this task will analyze and simulate an MHD power plant for any number of different configurations, and will hold constraints automatically while conducting either sensitivity studies or optimization. A summary of a sensitivity analysis conducted for a combined cycle, MHD-steam power plant is presented. The influence of several of the more important systems parameters were investigated in a systematic fashion, and the results are presented in graphical form. The report is divided into four sections. Following the introduction, the second section describes in detail the results of a validation study conducted to insure that the code is functioning correctly. The third section includes a description of the ANL cost algorithm and a detailed comparison between the ANL cost results and published OCMHD cost information. it is further demonstrated in this section that good agreement is obtained for the calculated cost of electricity. The fourth section is a sensitivity study and optimization for a specific OCMHD configuration over several key plant parameters.

  12. Resistive MHD studies of high-. beta. -tokamak plasmas

    SciTech Connect

    Lynch, V.E.; Carreras, B.A.; Hicks, H.R.; Holmes, J.A.; Garcia, L.

    1981-01-01

    Numerical calculations have been performed to study the MHD activity in high-..beta.. tokamaks such as ISX-B. These initial value calculations built on earlier low ..beta.. techniques, but the ..beta.. effects create several new numerical issues. These issues are discussed and resolved. In addition to time-stepping modules, our system of computer codes includes equilibrium solvers (used to provide an initial condition) and output modules, such as a magnetic field line follower and an X-ray diagnostic code. The transition from current driven modes at low ..beta.. to predominantly pressure driven modes at high ..beta.. is described. The nonlinear studies yield X-ray emissivity plots which are compared with experiment.

  13. A Numerical Study of Resistivity and Hall Effects for a Compressible MHD Model

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjogreen, B.

    2005-01-01

    The effect of resistive, Hall, and viscous terms on the flow structure compared with compressible ideal MHD is studied numerically for a one-fluid non-ideal MHD model. The goal of the present study is to shed some light on the emerging area of non-ideal MHD modeling and simulation. Numerical experiments are performed on a hypersonic blunt body flow with future application to plasma aerodynamics flow control in reentry vehicles. Numerical experiments are also performed on a magnetized time-developing mixing layer with possible application to magnetic/turbulence mixing.

  14. Scalable implicit incompressible resistive MHD with stabilized FE and fully-coupled Newton–Krylov-AMG

    DOE PAGES

    Shadid, J. N.; Pawlowski, R. P.; Cyr, E. C.; ...

    2016-02-10

    Here, we discuss that the computational solution of the governing balance equations for mass, momentum, heat transfer and magnetic induction for resistive magnetohydrodynamics (MHD) systems can be extremely challenging. These difficulties arise from both the strong nonlinear, nonsymmetric coupling of fluid and electromagnetic phenomena, as well as the significant range of time- and length-scales that the interactions of these physical mechanisms produce. This paper explores the development of a scalable, fully-implicit stabilized unstructured finite element (FE) capability for 3D incompressible resistive MHD. The discussion considers the development of a stabilized FE formulation in context of the variational multiscale (VMS) method,more » and describes the scalable implicit time integration and direct-to-steady-state solution capability. The nonlinear solver strategy employs Newton–Krylov methods, which are preconditioned using fully-coupled algebraic multilevel preconditioners. These preconditioners are shown to enable a robust, scalable and efficient solution approach for the large-scale sparse linear systems generated by the Newton linearization. Verification results demonstrate the expected order-of-accuracy for the stabilized FE discretization. The approach is tested on a variety of prototype problems, that include MHD duct flows, an unstable hydromagnetic Kelvin–Helmholtz shear layer, and a 3D island coalescence problem used to model magnetic reconnection. Initial results that explore the scaling of the solution methods are also presented on up to 128K processors for problems with up to 1.8B unknowns on a CrayXK7.« less

  15. The effects of differential flow between rational surfaces on toroidal resistive MHD modes

    NASA Astrophysics Data System (ADS)

    Brennan, Dylan; Halfmoon, Michael; Rhodes, Dov; Cole, Andrew; Okabayashi, Michio; Paz-Soldan, Carlos; Finn, John

    2016-10-01

    Differential flow between resonant surfaces can strongly affect the coupling and penetration of resonant components of resistive modes, and yet this mechanism is not yet fully understood. This study focuses on the evolution of tearing instabilities and the penetration of imposed resonant magnetic perturbations (RMPs) in tokamak configurations relevant to DIII-D and ITER, including equilibrium flow shear. It has been observed on DIII-D that the onset of tearing instabilities leading to disruption is often coincident with a loss of differential rotation between a higher m/n tearing surface (normally the 4/3 or 3/2) and a lower m/n tearing surface (normally the 2/1). Imposing RMPs can strongly affect this coupling and the torques between the modes. We apply the nonlinear 3-D resistive magnetohydrodynamic (MHD) code NIMROD to study the mechanisms by which these couplings occur. Reduced MHD analyses are applied to study the effects of differential flow between resonant surfaces in the simulations. Interaction between resonant modes can cause significant energy transfer between them, effectively stabilizing one mode while the other grows. The flow mitigates this transfer, but also affects the individual modes. The combination of these effects determines the nonlinear outcome. Supported by US DOE Grants DE-SC0014005 and DE-SC0014119.

  16. Coalescence of magnetic islands in the low-resistivity, Hall-MHD regime.

    PubMed

    Knoll, D A; Chacón, L

    2006-04-07

    The coalescence of magnetic islands in the low-resistivity eta, Hall-MHD regime is studied. The interaction between the ion inertial length d(i) and the dynamically evolving current sheet scale length deltaJ is established. Initially, d(i) < deltaJ. If eta is such that deltaJ dynamically thins down to d(i) prior to the well-known sloshing phenomena, then sloshing is avoided. This results in eta independent peak reconnection rates. However, if d(i) is small enough that deltaJ cannot be thinned down to this scale prior to sloshing, then sloshing proceeds as in the resistive MHD model.

  17. Proceedings of the workshop on nonlinear MHD and extended MHD

    SciTech Connect

    1998-12-01

    Nonlinear MHD simulations have proven their value in interpreting experimental results over the years. As magnetic fusion experiments reach higher performance regimes, more sophisticated experimental diagnostics coupled with ever expanding computer capabilities have increased both the need for and the feasibility of nonlinear global simulations using models more realistic than regular ideal and resistive MHD. Such extended-MHD nonlinear simulations have already begun to produce useful results. These studies are expected to lead to ever more comprehensive simulation models in the future and to play a vital role in fully understanding fusion plasmas. Topics include the following: (1) current state of nonlinear MHD and extended-MHD simulations; (2) comparisons to experimental data; (3) discussions between experimentalists and theorists; (4) /equations for extended-MHD models, kinetic-based closures; and (5) paths toward more comprehensive simulation models, etc. Selected papers have been indexed separately for inclusion in the Energy Science and Technology Database.

  18. Non-linear MHD Simulation of ELMs including Pellet Triggered ones for KSTAR tokamak

    NASA Astrophysics Data System (ADS)

    Han, Hyunsun; Park, G.; Strauss, H.; Kim, J. Y.

    2011-10-01

    Three-dimensional non-linear MHD simulations have been conducted to investigate the qualitative characteristics of ELM(Edge Localized Mode)s including pellet induced ones using the M3D code. A linearized velocity perturbation of initial equilibrium is employed to trigger the ELM instability for the simulation of natural ELM, while a density blob, which represents the ionized pellet ablation and is located within the edge pedestal, is adopted in an adiabatic condition for that of pellet induced one. The initial equilibrium is constructed based on a H-mode plasma of KSTAR(Korea Superconducting Tokamak Advanced Research) device. It is found that characteristics of natural ELM simulation are in qualitative agreement with the experimental observations including that density perturbation is much larger than temperature one during ELM instability. Regarding the pellet induced ELM, it is observed that the locally increased pressure due to the fast parallel heat conduction compared to the spread of density perturbation triggers the peeling-ballooning instability resulting in ELM-like relaxation. Detailed results will be presented in the discussion of underlying mechanism and application to KSTAR tokamak.

  19. Computational modeling of neoclassical and resistive MHD tearing modes in tokamaks

    SciTech Connect

    Gianakon, Thomas A.

    1996-02-01

    Numerical studies of the linear and nonlinear evolution of magnetic tearing type modes in three-dimensional toroidal geometry are presented. In addition to traditional resistive MHD effects, where the parameter Δ' determines the stability properties, neoclassical effects have been included for the first time in such models. The inclusion of neoclassical physics introduces and additional free-energy source for the nonlinear formation of magnetic islands through the effects of a bootstrap current in Ohm`s law. The neoclassical tearing mode is demonstrated to be destabilized in plasmas which are otherwise Δ' stable, albeit once an island width threshold is exceeded. The simulations are based on a set of neoclassical reduced magnetohydrodynamic (MHD) equations in three-dimensional toroidal geometry derived from the two-fluid equations in the limit of small inverse aspect ratio ε and low plasma pressure β with neoclassical closures for the viscous force ∇• $\\vec{π}$. The poloidal magnetic flux Ψ, the toroidal vorticity ωζ, and the plasma pressure p are time advanced using the parallel projection of Ohm`s law, the toroidal projection of the curl of the momentum equation, and a pressure evolution equation with anisotropic pressure transport parallel to and across magnetic field lines. The equations are implemented in an initial value code which Fourier decomposes equilibrium and perturbation quantities in the poloidal and toroidal directions, and finite differences them radially based on a equilibrium straight magnetic field line representation. An implicit algorithm is used to advance the linear terms; the nonlinear terms are advanced explicitly. The simulations are benchmarked linearly and nonlinearly against single and multiple helicity Δ' tearing modes in toroidal geometry in the absence of neo-classical effects.

  20. A Numerical Approach to Solving the Hall MHD Equations Including Diamagnetic Drift (Preprint)

    DTIC Science & Technology

    2008-02-19

    References [1] J. Birn and et al. Geospace environmental modeling (gem) magnetic reconnection challenge. Journal of Geophysical Research, 106(A3):3715–3719...equations. Journal of Computational Physics, 179:495–538, 2002. [21] A. Otto. Geospace environment modeling (gem) magnetic reconnection challenge: Mhd

  1. Impact of resistive MHD plasma response on perturbation field sidebands

    NASA Astrophysics Data System (ADS)

    Orlov, D. M.; Evans, T. E.; Moyer, R. A.; Lyons, B. C.; Ferraro, N. M.; Park, G.-Y.

    2016-07-01

    Single fluid linear simulations of a KSTAR RMP ELM suppressed discharge with the M3D-C1 resistive magnetohydrodynamic code have been performed for the first time. The simulations show that the application of the n  =  1 perturbation using the KSTAR in-vessel control coils (IVCC), which apply modest levels of n  =  3 sidebands (~20% of the n  =  1), leads to levels of n  =  3 sideband that are comparable to the n  =  1 when plasma response is included. This is due to the reduced level of screening of the rational-surface-resonant n  =  3 component relative to the rational-surface-resonant n  =  1 component. The n  =  3 sidebands could play a similar role in ELM suppression on KSTAR as the toroidal sidebands (n  =  1, 2, 4) in DIII-D n  =  3 ELM suppression with missing I-coil segments (Paz Soldan et al 2014 Nucl. Fusion 54 073013). This result may help to explain the uniqueness of ELM suppression with n  =  1 perturbations in KSTAR since the effective perturbation is a mixed n  =  1/n  =  3 perturbation similar to n  =  3 ELM suppression in DIII-D.

  2. Linear Analysis of the m=0 Instability for a Visco-resistive Hall MHD Plasma

    SciTech Connect

    Oliver, B.V.; Genoni, T.C.; Mehlhorn, T.A.

    2006-01-05

    We present a comprehensive analysis of the linear dispersion relation for the axisymmetric (m=0) compressible interchange instability of Bennett equilibria in a visco-resistive, Hall MHD plasma. The full anisotropic stress tensor with Braginskii viscous coefficients is considered. The eigenvalues are obtained numerically. For small axial mode number, Hall currents enhance the growth rates, whereas in the limit of high mode number the growth rates are suppressed, eventually resulting in wave cutoff, even in the ideal limit. For the visco-resistive plasma the unstable spectra are weakly dependent on the off-diagonal elements of the stress tensor.

  3. Ideal and resistive MHD stability of one-dimensional tokamak equilibria

    SciTech Connect

    Chance, M.S.; Furth, H.P.; Glasser, A.H.; Selberg, H.

    1981-07-01

    The MHD equilibrium and stability of a vertically elongated tokamak configuration are analyzed in the one-dimensional limit corresponding to infinite elongation. Stability against all ideal MHD modes can be obtained for beta-values arbitrarily close to unity. In the finite-resistivity stability analysis, axisymmetric (m = 0) tearing modes, centered on the null trace of the poloidal field, can be stabilized by a loosely fitting conducting shell. The presence of the toroidal field component, however, introduces the possibility of nonsymmetric tearing modes (m not equal to 0), centered away from the null trace. These modes can be stabilized only by a more tightly-fitting shell, plus reliance on finite-pressure effects on the small-major-radius side of the plasma profile. Under these conditions, stable configurations with peak beta values approaching unity are readily found.

  4. A Coupled MHD and Thermal Model Including Electrostatic Sheath for Magnetoplasmadynamic Thruster Simulation

    NASA Astrophysics Data System (ADS)

    Kawasaki, Akira; Kubota, Kenichi; Funaki, Ikkoh; Okuno, Yoshihiro

    2016-09-01

    Steady-state and self-field magnetoplasmadynamic (MPD) thruster, which utilizes high-intensity direct-current (DC) discharge, is one of the prospective candidates of future high-power electric propulsion devices. In order to accurately assess the thrust performance and the electrode temperature, input electric power and wall heat flux must correctly be evaluated where electrostatic sheaths formed in close proximity of the electrodes affect these quantities. Conventional model simulates only plasma flows occurring in MPD thrusters with the absence of electrostatic sheath consideration. Therefore, this study extends the conventional model to a coupled magnetohydrodynamic (MHD) and thermal model by incorporating the phenomena relevant to the electrostatic sheaths. The sheaths are implemented as boundary condition of the MHD model on the walls. This model simulated the operation of the 100-kW-class thruster at discharge current ranging from 6 to 10 kA with argon propellant. The extended model reproduced the discharge voltages and wall heat load which are consistent with past experimental results. In addition, the simulation results indicated that cathode sheath voltages account for approximately 5-7 V subject to approximately 20 V of discharge voltages applied between the electrodes. This work was supported by JSPS KAKENHI Grant Numbers 26289328 and 15J10821.

  5. Modeling of magnetic reconnection in the magnetotail using global MHD simulation with an effective resistivity model

    NASA Astrophysics Data System (ADS)

    Den, M.; Horiuchi, R.; Fujita, S.; Tanaka, T.

    2011-12-01

    Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Tanaka and Fujita reproduced substorm evolution process by numerical simulation with the global MHD code [1]. In the MHD framework, the dissipation model is introduced for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dissipation model employed there, gave a large effect for the dipolarization, central phenomenon in the substorm development process, though that viscosity was assumed to be a constant parameter. It is well known that magnetic reconnection is controlled by microscopic kinetic mechanism. Frozen-in condition is broken due to particle kinetic effects and collisionless reconnection is triggered when current sheet is compressed as thin as ion kinetic scales under the influence of external driving flow [2, 3]. Horiuchi and his collaborators showed that reconnection electric field generated by microscopic physics evolves inside ion meandering scale so as to balance the flux inflow rate at the inflow boundary, which is controlled by macroscopic physics [2]. That is, effective resistivity generated through this process can be expressed by balance equation between micro and macro physics. In this paper, we perform substorm simulation by using the global MHD code developed by Tanaka [3] with this effective resistivity instead of the empirical resistivity model. We obtain the AE indices from simulation data, in which substorm onset can be seen clearly, and investigate the relationship between the substorm development and the effective resistivity model. [1] T. Tanaka, A, Nakamizo, A. Yoshikawa, S. Fujita, H. Shinagawa, H. Shimazu, T. Kikuchi, and K. K. Hashimoto, J. Geophys. Res. 115 (2010) A05220,doi:10.1029/2009JA014676. [2] W. Pei, R. Horiuchi, and T. Sato, Physics of Plasmas,Vol. 8 (2001), pp. 3251-3257. [3] A. Ishizawa, and R. Horiuchi, Phys. Rev. Lett., Vol. 95, 045003 (2005). [4

  6. Heat transfer including radiation and slag particles evolution in MHD channel-I

    SciTech Connect

    Im, K H; Ahluwalia, R K

    1980-01-01

    Accurate estimates of convective and radiative heat transfer in the magnetohydrodynamic channel are provided. Calculations performed for a base load-size channel indicate that heat transfer by gas radiation almost equals that by convection for smooth walls, and amounts to 70% as much as the convective heat transfer for rough walls. Carbon dioxide, water vapor, and potassium atoms are the principal participating gases. The evolution of slag particles by homogeneous nucleation and condensation is also investigated. The particle-size spectrum so computed is later utilized to analyze the radiation enhancement by slag particles in the MHD diffuser. The impact of the slag particle spectrum on the selection of a workable and design of an efficient seed collection system is discussed.

  7. Structure of the dayside reconnection layer in resistive MHD and hybrid models

    NASA Technical Reports Server (NTRS)

    Lin, Y.; Lee, L. C.

    1993-01-01

    Numerical simulations were performed to investigate the structure of the reconnection layer at the dayside magnetopause. Two typical cases are examined in detail; both are asymmetric in magnetic field and plasma density. In case 1, the guide fields in the magnetosheath and in the magnetosphere are set at zero and thus the tangential magnetic fields on the two sides of the initial current sheet are exactly antiparallel. In case 2, the angle between the tangential magnetic fields on the two sides of the initial current sheet is 145 deg. The results obtained from a resistive MHD model and from a hybrid model are found to be different. In the MHD simulation of case 1, a 2-4 intermediate shock is found to bound the reconnection layer on the magnetosheath side, while an Alfven wave pulse bounds the reconnection layer on the magnetospheric side. In case 2, it is found that a time-dependent intermediate shock (TDIS) bounds the reconnection layer on the magnetosheath side, with a slow expansion wave propagating behind. With the MHD simulations, in the general case in which the tangential magnetic fields on the two sides of the initial current sheet are not exactly antiparallel, a rotational discontinuity across which the tangential magnetic field rotates, a large angle is found to bound the reconnection layer on the magnetosheath side.

  8. Minimally implicit Runge-Kutta methods for Resistive Relativistic MHD

    NASA Astrophysics Data System (ADS)

    Aloy, Miguel-Á.; Cordero-Carrión, Isabel

    2016-05-01

    The Relativistic Resistive Magnetohydrodynamic (RRMHD) equations are a hyperbolic system of partial differential equations used to describe the dynamics of relativistic magnetized fluids with a finite conductivity. Close to the ideal magnetohydrodynamic regime, the source term proportional to the conductivity becomes potentially stiff and cannot be handled with standard explicit time integration methods. We propose a new class of methods to deal with the stiffness fo the system, which we name Minimally Implicit Runge-Kutta methods. These methods avoid the development of numerical instabilities without increasing the computational costs in comparison with explicit methods, need no iterative extra loop in order to recover the primitive (physical) variables, the analytical inversion of the implicit operator is trivial and the several stages can actually be viewed as stages of explicit Runge-Kutta methods with an effective time-step. We test these methods with two different one-dimensional test beds in varied conductivity regimes, and show that our second-order schemes satisfy the theoretical expectations.

  9. Transient Phenomena of Disk MHD Generator due to Change of Load Resistance

    NASA Astrophysics Data System (ADS)

    Koka, Hidetoshi; Okuno, Yoshihiro; Yamasaki, Hiroyuki

    Results of experimental study on transient phenomena of the closed cycle disk MHD generator are described in this paper. The transient phenomena were caused by a step-like change of load resistance during a test time of the shock-tube driven disk MHD generator. The load resistance was changed by using an IGBT (Insulated Gate Bipolar Transistor) installed in a load circuit. When the load resistance was changed from 0.096Ω to 2.5Ω, an overshoot of the Hall output voltage and of the Hall electric field was observed, and a large fluctuation of static pressure was also observed. At the same time, a spike-like increase of cesium recombination continuum and line spectrum appeared just after the load change. Results of the quasi-one dimensional numerical simulation have indicated that the observed overshoot was caused by the following phenomena: 1) a steep reduction of the Hall current and a steep increase in both the Faraday current and the electrical conductivity, and 2) a slow reduction of gas velocity due to the enhanced retarding force. Furthermore, the measured spike-like increase of radiation intensity was ascribed to an increase of electron temperature and electron number density by a steep increase of Joule heating.

  10. Local Existence for the Non-Resistive MHD Equations in Nearly Optimal Sobolev Spaces

    NASA Astrophysics Data System (ADS)

    Fefferman, Charles L.; McCormick, David S.; Robinson, James C.; Rodrigo, Jose L.

    2017-02-01

    This paper establishes the local-in-time existence and uniqueness of solutions to the viscous, non-resistive magnetohydrodynamics (MHD) equations in {R^d}, where d = 2, 3, with initial data {B_0in H^s(R^d)} and {u_0in H^{s-1+ɛ}(R^d)} for {s > d/2} and any {0 < ɛ < 1}. The proof relies on maximal regularity estimates for the Stokes equation. The obstruction to taking {ɛ=0} is explained by the failure of solutions of the heat equation with initial data {u_0in H^{s-1}} to satisfy {uin L^1(0,T; H^{s+1})}; we provide an explicit example of this phenomenon.

  11. MHD Instabilities Occurring Near/AT the Transport Barrier, Including Loss of Confinement in H-Modes

    SciTech Connect

    L. L. Lao

    1999-09-01

    In configurations with transport barriers the improved edge and core confinement leads to large pressure gradient and large edge bootstrap current density which often drive magnetohydrodynamic (MHD) instabilities terminating the discharge or reducing the discharge performance. The edge and the core transport barriers deteriorate or are completely lost. In this presentation, recent experimental and theoretical developments concerning MHD instabilities occurring near/at the edge and the core transport barriers are summarized emphasizing the dominant instabilities and the comparison with theory.

  12. MHD Simulations of Coronal Supra-arcade Downflows Including Anisotropic Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Zurbriggen, E.; Costa, A.; Esquivel, A.; Schneiter, M.; Cécere, M.

    2016-11-01

    Coronal supra-arcade downflows (SADs) are observed as dark trails descending toward hot turbulent-fan-shaped regions. Due to the large temperature values and gradients in these fan regions, the thermal conduction (TC) should be very efficient. While several models have been proposed to explain the triggering and the evolution of SADs, none of these scenarios address a systematic consideration of TC. Thus, we accomplish this task numerically simulating the evolution of SADs within this framework. That is, SADs are conceived as voided (subdense) cavities formed by nonlinear waves triggered by downflowing bursty localized reconnection events in a perturbed hot fan. We generate a properly turbulent fan, obtained by a stirring force that permits control of the energy and vorticity input in the medium where SADs develop. We include anisotropic TC and consider plasma properties consistent with observations. Our aim is to study whether it is possible to prevent SADs from vanishing by thermal diffusion. We find that this will be the case, depending on the turbulence parameters, in particular if the magnetic field lines are able to envelope the voided cavities, thermally isolating them from the hot environment. Velocity shear perturbations that are able to generate instabilities of the Kelvin-Helmholtz type help to produce magnetic islands, extending the lifetime of SADs.

  13. Global well-posedness for the incompressible MHD equations with density-dependent viscosity and resistivity coefficients

    NASA Astrophysics Data System (ADS)

    Si, Xin; Ye, Xia

    2016-10-01

    This paper concerns an initial-boundary value problem of the inhomogeneous incompressible MHD equations in a smooth bounded domain. The viscosity and resistivity coefficients are density-dependent. The global well-posedness of strong solutions is established, provided the initial norms of velocity and magnetic field are suitably small in some sense, or the lower bound of the transport coefficients are large enough. More importantly, there is not any smallness condition on the density and its gradient.

  14. rHARM: Accretion and Ejection in Resistive GR-MHD

    NASA Astrophysics Data System (ADS)

    Qian, Qian; Fendt, Christian; Noble, Scott; Bugli, Matteo

    2017-01-01

    Turbulent magnetic diffusivity plays an important role for accretion disks and the launching of disk winds. We have implemented magnetic diffusivity and respective resistivity in the general relativistic MHD code HARM. This paper describes the theoretical background of our implementation, its numerical realization, our numerical tests, and preliminary applications. The test simulations of the new code rHARM are compared to an analytic solution of the diffusion equation and a classical shock tube problem. We have further investigated the evolution of the magnetorotational instability (MRI) in tori around black holes (BHs) for a range of magnetic diffusivities. We find an indication for a critical magnetic diffusivity (for our setup) beyond which no MRI develops in the linear regime and for which accretion of torus material to the BH is delayed. Preliminary simulations of magnetically diffusive thin accretion disks around Schwarzschild BHs that are threaded by a large-scale poloidal magnetic field show the launching of disk winds with mass fluxes of about 50% of the accretion rate. The disk magnetic diffusivity allows for efficient disk accretion that replenishes the mass reservoir of the inner disk area and thus allows for long-term simulations of wind launching for more than 5000 time units.

  15. Supersonic MHD generator system

    SciTech Connect

    Rahman, M.A.

    1983-11-29

    An improved MHD electrical power generating system of the type having a MHD topping cycle and a steam generating bottoming cycle is disclosed. The system typically includes a combustion system, a conventional MHD generator and a first diffuser radiant boiler. The improvement comprises a first supersonic MHD generator and ramjet engine configuration operatively connected in series with each other and with the conventional MHD generator. The first supersonic MHD generator and ramjet engine configuration increase the power output and improve the operating efficiency of the electrical generating system. A diffuser system is also disclosed which is in fluid communication with the supersonic MHD generator and the ramjet engine for collecting bypass plasma gas to be used for heating a second radiant boiler adapted for powering a steam turbine generator.

  16. Global existence and uniqueness theorem to 2-D incompressible non-resistive MHD system with non-equilibrium background magnetic field

    NASA Astrophysics Data System (ADS)

    Zhai, Cuili; Zhang, Ting

    2016-09-01

    In this article, we consider the global existence and uniqueness of the solution to the 2D incompressible non-resistive MHD system with non-equilibrium background magnetic field. Our result implies that a strong enough non-equilibrium background magnetic field will guarantee the stability of the nonlinear MHD system. Beside the classical energy method, the interpolation inequalities and the algebraic structure of the equations coming from the incompressibility of the fluid are crucial in our arguments.

  17. MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column

    NASA Astrophysics Data System (ADS)

    Striani, E.; Mignone, A.; Vaidya, B.; Bodo, G.; Ferrari, A.

    2016-11-01

    Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as S1/2 (where S is the Lundquist number) and yields time-scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of S (`fast reconnection' regime) due to the presence of the secondary tearing instability that takes place for S ≳ 1 × 104. We report on our 3D MHD simulations of magnetic reconnection in a magnetically confined cylindrical plasma column under either a pressure balanced or a force-free equilibrium and compare the results with 2D simulations of a circular current sheet. We find that the 3D instabilities acting on these configurations result in a fragmentation of the initial current sheet in small filaments, leading to enhanced dissipation rate that becomes independent of the Lundquist number already at S ≃ 1 × 103.

  18. Modeling of fast neutral-beam-generated ion effects on MHD-spectroscopic observations of resistive wall mode stability in DIII-D plasmas

    SciTech Connect

    Turco, F. Hanson, J. M.; Navratil, G. A.; Turnbull, A. D.

    2015-02-15

    Experiments conducted at DIII-D investigate the role of drift kinetic damping and fast neutral beam injection (NBI)-ions in the approach to the no-wall β{sub N} limit. Modelling results show that the drift kinetic effects are significant and necessary to reproduce the measured plasma response at the ideal no-wall limit. Fast neutral-beam ions and rotation play important roles and are crucial to quantitatively match the experiment. In this paper, we report on the model validation of a series of plasmas with increasing β{sub N}, where the plasma stability is probed by active magnetohydrodynamic (MHD) spectroscopy. The response of the plasma to an externally applied field is used to probe the stable side of the resistive wall mode and obtain an indication of the proximity of the equilibrium to an instability limit. We describe the comparison between the measured plasma response and that calculated by means of the drift kinetic MARS-K code [Liu et al., Phys. Plasmas 15, 112503 (2008)], which includes the toroidal rotation, the electron and ion drift-kinetic resonances, and the presence of fast particles for the modelled plasmas. The inclusion of kinetic effects allows the code to reproduce the experimental results within ∼13% for both the amplitude and phase of the plasma response, which is a significant improvement with respect to the undamped MHD-only model. The presence of fast NBI-generated ions is necessary to obtain the low response at the highest β{sub N} levels (∼90% of the ideal no-wall limit). The toroidal rotation has an impact on the results, and a sensitivity study shows that a large variation in the predicted response is caused by the details of the rotation profiles at high β{sub N}.

  19. Extended-MHD modeling of diamagnetic-drift tearing instabilities

    NASA Astrophysics Data System (ADS)

    King, Jacob; Kruger, Scott

    2012-03-01

    We use analytics and computations with the NIMROD code to examine tearing stability in large-guide-field slab cases with a nonzero equilibrium pressure gradient. A well known result from drift-reduced MHD is the diamagnetic drift associated with the pressure gradient has a stabilizing influence were the dispersion relation becomes (γ+iφ*e)^3γ(γ+iφ*i)=γrMHD^5 [1]. Here φ*i and φ*e are the ion- and electron-diamagnetic frequencies and γrMHD is the tearing growth rate with a resistive-MHD model. Preliminary computational results with an unreduced extended-MHD model do not produce the expected drift-reduced result. For moderate values of φ*i (φ*i<=3γrMHD), the computations follow the dispersion relation that would result if the ∇pe term were not included in the drift-reduced parallel Ohm's law: (γ+iφ*e)^4(γ+iφ*i)=γrMHD^5. Analytics, guided by computational diagnostics, are used to examine the significant terms in the flux evolution equation and investigate the discrepancy with the drift-reduced result.[4pt] [1] For example Coppi, PoF 7, 1501 (1964); Biskamp, NF 18, 1059 (1978).

  20. Sugarcane aphid (Hemiptera: Aphididae): Host range and sorghum resistance including cross-resistance from greenbug sources

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The graminous host range, and sources of sorghum plant resistance including cross resistance from greenbug, Schizaphis graminum (Rond.) sorghums, [Sorghum bicolor L.) Moench], were studied for the newly emerging sugarcane aphid Melanaphis sacchari, (Zehntner) in greenhouse no-choice experiments and ...

  1. MHD Stagnation point flows in the presence of resistivity and viscosity

    SciTech Connect

    Gratton, F.T.; Heyn, M.F.; Biernat, H.K.; Rijnbeek, R.P.; Gnavi, G. )

    1988-07-01

    The authors analyze the steady state situation in which two separate and counterstreaming plasmas (assumed to be incompressible) carrying antiparallel magnetic fields are separated by a resistive current layer. Exact solutions are presented which describe the stagnation point flow pattern and magnetic field behavior which result. They incorporate the effects of viscosity, which enables us to model flows with vorticity. The uniform plasma flow which is obtained at large distances from the current layer allows us to specify finite values of the asymptotic magnetic field. The exact solutions complement those of a different type obtained by B.U.O. Sonnerup and E.R. Priest (1975) which assume potential flow, i.e., zero vorticity. The results they obtain are discussed in relation to observational features at the Earth's magnetopause.

  2. Resistive tearing instability in electron MHD: application to neutron star crusts

    NASA Astrophysics Data System (ADS)

    Gourgouliatos, Konstantinos N.; Hollerbach, Rainer

    2016-12-01

    We study a resistive tearing instability developing in a system evolving through the combined effect of Hall drift in the electron magnetohydrodynamic limit and Ohmic dissipation. We explore first the exponential growth of the instability in the linear case and we find the fastest growing mode, the corresponding eigenvalues and dispersion relation. The instability growth rate scales as γ ∝ B2/3σ-1/3, where B is the magnetic field and σ the electrical conductivity. We confirm the development of the tearing resistive instability in the fully non-linear case, in a plane-parallel configuration where the magnetic field polarity reverses, through simulations of systems initiating in Hall equilibrium with some superimposed perturbation. Following a transient phase, during which there is some minor rearrangement of the magnetic field, the perturbation grows exponentially. Once the instability is fully developed, the magnetic field forms the characteristic islands and X-type reconnection points, where Ohmic decay is enhanced. We discuss the implications of this instability for the local magnetic field evolution in neutron stars' crusts, proposing that it can contribute to heating near the surface of the star, as suggested by models of magnetar post-burst cooling. In particular, we find that a current sheet a few metres thick, covering as little as 1 per cent of the total surface, can provide 1042 erg in thermal energy within a few days. We briefly discuss applications of this instability in other systems where the Hall effect operates such as protoplanetary discs and space plasmas.

  3. Salient issues of edge physics pertaining to loss of confinement: A resistive MHD analysis

    SciTech Connect

    Thayer, D.R.

    1991-01-01

    The progress that has been made during this fiscal year is significant in the area of tokamak edge plasma transport. The drift-rippling mode model of edge turbulent transport was extended. In particular, the research areas on which were concentrated include the following topics: (1) The theoretical investigation of the radiatively enhanced transport due to the effects of impurity driven radiation instabilities has been expanded to include a situation with multiple impurities (such as carbon, C{sup 4+}, and oxygen, O{sup 6+}); (2) In order to validate the use of the impurity radiation input from the tokamak bolometer experiments in the theoretical edge turbulent transport calculations, the analysis that is utilized to transform impurity brightness data to radiated power profiles has been checked for state population and Abel inversion correctness; (3) The drift-rippling model of edge turbulent transport has been extended to include ionization particle sources in addition to the impurity driven thermal instability drive; and (4) The detailed limiter and realistic edge geometric effects on the edge turbulent transport has been included in the drift-rippling model.

  4. MHD Program Plan, FY 1992

    NASA Astrophysics Data System (ADS)

    1991-10-01

    The current MHD program being implemented is a result of a consensus established in public meetings held by the Department of Energy in 1984. Essential elements of the current program include the following: (1) develop technical and environmental data for the integrated MHD topping cycle system through POC testing (1,000 hours); (2) develop technical and environmental data for the integrated MHD bottoming cycle sub system through POC testing (4,000 hours); (3) design, construct, and operate a seed regeneration POC facility (SRPF) capable of processing spent seed materials from the MHD bottoming cycle; (4) prepare conceptual designs for a site specific MHD retrofit plant; and (5) continue system studies and supporting research necessary for system testing. The current MHD program continues to be directed toward coal fired power plant applications, both stand-alone and retrofit. Development of a plant should enhance the attractiveness of MHD for applications other than electrical power. MHD may find application in electrical energy intensive industries and in the defense sector.

  5. Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

    SciTech Connect

    Hirshman, S. P.; Shafer, M. W.; Seal, S. K.; Canik, J. M.

    2016-03-03

    The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant m=2, n=-1 , resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the m=2 (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces) of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.

  6. Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

    DOE PAGES

    Hirshman, S. P.; Shafer, M. W.; Seal, S. K.; ...

    2016-03-03

    The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant m=2, n=-1 , resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the m=2 (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces)more » of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.« less

  7. MHD Energy Bypass Scramjet Engine

    NASA Technical Reports Server (NTRS)

    Mehta, Unmeel B.; Bogdanoff, David W.; Park, Chul; Arnold, Jim (Technical Monitor)

    2001-01-01

    Revolutionary rather than evolutionary changes in propulsion systems are most likely to decrease cost of space transportation and to provide a global range capability. Hypersonic air-breathing propulsion is a revolutionary propulsion system. The performance of scramjet engines can be improved by the AJAX energy management concept. A magneto-hydro-dynamics (MHD) generator controls the flow and extracts flow energy in the engine inlet and a MHD accelerator downstream of the combustor accelerates the nozzle flow. A progress report toward developing the MHD technology is presented herein. Recent theoretical efforts are reviewed and ongoing experimental efforts are discussed. The latter efforts also include an ongoing collaboration between NASA, the US Air Force Research Laboratory, US industry, and Russian scientific organizations. Two of the critical technologies, the ionization of the air and the MHD accelerator, are briefly discussed. Examples of limiting the combustor entrance Mach number to a low supersonic value with a MHD energy bypass scheme are presented, demonstrating an improvement in scramjet performance. The results for a simplified design of an aerospace plane show that the specific impulse of the MHD-bypass system is better than the non-MHD system and typical rocket over a narrow region of flight speeds and design parameters. Equilibrium ionization and non-equilibrium ionization are discussed. The thermodynamic condition of air at the entrance of the engine inlet determines the method of ionization. The required external power for non-equilibrium ionization is computed. There have been many experiments in which electrical power generation has successfully been achieved by magneto-hydrodynamic (MHD) means. However, relatively few experiments have been made to date for the reverse case of achieving gas acceleration by the MHD means. An experiment in a shock tunnel is described in which MHD acceleration is investigated experimentally. MHD has several

  8. Resistive reduced MHD modeling of multi-edge-localized-mode cycles in Tokamak X-point plasmas.

    PubMed

    Orain, F; Bécoulet, M; Huijsmans, G T A; Dif-Pradalier, G; Hoelzl, M; Morales, J; Garbet, X; Nardon, E; Pamela, S; Passeron, C; Latu, G; Fil, A; Cahyna, P

    2015-01-23

    The full dynamics of a multi-edge-localized-mode (ELM) cycle is modeled for the first time in realistic tokamak X-point geometry with the nonlinear reduced MHD code jorek. The diamagnetic rotation is found to be instrumental to stabilize the plasma after an ELM crash and to model the cyclic reconstruction and collapse of the plasma pressure profile. ELM relaxations are cyclically initiated each time the pedestal gradient crosses a triggering threshold. Diamagnetic drifts are also found to yield a near-symmetric ELM power deposition on the inner and outer divertor target plates, consistent with experimental measurements.

  9. MHD turbulent processes

    NASA Technical Reports Server (NTRS)

    Montgomery, David

    1988-01-01

    Three areas of study in MHD turbulence are considered. These are the turbulent relaxation of the toroidal Z pinch, density fluctuations in MHD fluids, and MHD cellular automata. A Boolean computer game that updates a cellular representation in parallel and that has macroscopic averages converging to solutions of the two-dimensional MHD equations is discussed.

  10. Modeling of fast neutral-beam-generated ion effects on MHD-spectroscopic observations of resistive wall mode stability in DIII-D plasmas [Modeling of fast neutral-beam-generated ion effects on MHD spectroscopic observations of RWM stability in DIII-D plasmas

    DOE PAGES

    Turco, Francesca; Turnbull, Alan D.; Hanson, Jeremy M.; ...

    2015-02-03

    Experiments conducted at DIII-D investigate the role of drift kinetic damping and fast neutral beam injection (NBI)-ions in the approach to the no-wall βN limit. Modelling results show that the drift kinetic effects are significant and necessary to reproduce the measured plasma response at the ideal no-wall limit. Fast neutral-beam ions and rotation play important roles and are crucial to quantitatively match the experiment. In this paper, we report on the model validation of a series of plasmas with increasing βN, where the plasma stability is probed by active magnetohydrodynamic (MHD) spectroscopy. The response of the plasma to an externallymore » applied field is used to probe the stable side of the resistive wall mode and obtain an indication of the proximity of the equilibrium to an instability limit. We describe the comparison between the measured plasma response and that calculated by means of the drift kinetic MARS-K code, which includes the toroidal rotation, the electron and ion drift-kinetic resonances, and the presence of fast particles for the modelled plasmas. The inclusion of kinetic effects allows the code to reproduce the experimental results within ~13% for both the amplitude and phase of the plasma response, which is a significant improvement with respect to the undamped MHD-only model. The presence of fast NBI-generated ions is necessary to obtain the low response at the highest βN levels (~90% of the ideal no-wall limit). Finally, the toroidal rotation has an impact on the results, and a sensitivity study shows that a large variation in the predicted response is caused by the details of the rotation profiles at high βN.« less

  11. Modeling of fast neutral-beam-generated ion effects on MHD-spectroscopic observations of resistive wall mode stability in DIII-D plasmas [Modeling of fast neutral-beam-generated ion effects on MHD spectroscopic observations of RWM stability in DIII-D plasmas

    SciTech Connect

    Turco, Francesca; Turnbull, Alan D.; Hanson, Jeremy M.; Navratil, Gerald A.

    2015-02-03

    Experiments conducted at DIII-D investigate the role of drift kinetic damping and fast neutral beam injection (NBI)-ions in the approach to the no-wall βN limit. Modelling results show that the drift kinetic effects are significant and necessary to reproduce the measured plasma response at the ideal no-wall limit. Fast neutral-beam ions and rotation play important roles and are crucial to quantitatively match the experiment. In this paper, we report on the model validation of a series of plasmas with increasing βN, where the plasma stability is probed by active magnetohydrodynamic (MHD) spectroscopy. The response of the plasma to an externally applied field is used to probe the stable side of the resistive wall mode and obtain an indication of the proximity of the equilibrium to an instability limit. We describe the comparison between the measured plasma response and that calculated by means of the drift kinetic MARS-K code, which includes the toroidal rotation, the electron and ion drift-kinetic resonances, and the presence of fast particles for the modelled plasmas. The inclusion of kinetic effects allows the code to reproduce the experimental results within ~13% for both the amplitude and phase of the plasma response, which is a significant improvement with respect to the undamped MHD-only model. The presence of fast NBI-generated ions is necessary to obtain the low response at the highest βN levels (~90% of the ideal no-wall limit). Finally, the toroidal rotation has an impact on the results, and a sensitivity study shows that a large variation in the predicted response is caused by the details of the rotation profiles at high βN.

  12. Nuclear MHD Converter

    DTIC Science & Technology

    2007-11-02

    model the Power Conversion Unit (gas reactor + nozzle and MHD channel), and the cross sections derived from Task 1.. The configuration extends ...8 1.1 Project Objectives 8 1.2 Report Organization 9 Tables and Figures 10 2 PROJECT DESCRIPTION 11 3 REFLECTOR MODELING 13 3.1 Symbols...outlet. This conclusion remains true even if the effect of dissociation and attachment are included in the numerical model . Furthermore, a

  13. Investigation of island formation due to RMPs in DIII-D plasmas with the SIESTA resistive MHD equilibrium code

    SciTech Connect

    Hirshman, S. P.; Shafer, M. W.; Seal, S. K.; Canik, J. M.

    2016-03-03

    The SIESTA magnetohydrodynamic (MHD) equilibrium code has been used to compute a sequence of ideally stable equilibria resulting from numerical variation of the helical resonant magnetic perturbation (RMP) applied to an axisymmetric DIII-D plasma equilibrium. Increasing the perturbation strength at the dominant $m=2$,$n=-1$ resonant surface leads to lower MHD energies and increases in the equilibrium island widths at the $m=2$ (and sidebands) surfaces, in agreement with theoretical expectations. Island overlap at large perturbation strengths leads to stochastic magnetic fields which correlate well with the experimentally inferred field structure. The magnitude and spatial phase (around the dominant rational surfaces) of the resonant (shielding) component of the parallel current are shown to change qualitatively with the magnetic island topology.

  14. MHD edge instabilities in toroidal plasmas

    NASA Astrophysics Data System (ADS)

    Sugiyama, Linda

    2015-11-01

    Different types of MHD edge instabilities in different toroidal magnetically confined plasmas are compared. Large scale numerical simulations show that the nonlinear evolution of an unstable edge mode in a shaped plasma with a single X-point and a surrounding open field line region has a number of common features in the full resistive MHD model for strongly unstable and weaker instabilities. These include the relation of the nonlinear mode structure and dominant toroidal harmonics to the linear eigenmode spectrum, the effects of the mode on reducing the edge pressure or density gradient, the inward penetration of a ballooning-type perturbation into the plasma interior, and the potential to drive a coherent axisymmetric poloidal rotation of the outer part of the plasma, exhibited at different strengths. The results can be compared to experiment to estimate the usefulness and validity of the MHD model for predicting edge stability and instability properties. Work supported by the U.S. DOE OFES under Awards DE-SC-0007883, DE-FG02-04ER54802, and DE-SC-0008737. Some computation carried out at NERSC.

  15. MHD Spectroscopy

    SciTech Connect

    Heeter, R F; Fasoli, A; Testa, D; Sharapov, S; Berk, H L; Breizman, B; Gondhalekar, A; Mantsinen, M

    2004-03-23

    Experiments are conducted on the JET tokamak to assess the diagnostic potential of MHD active and passive spectroscopy, for the plasma bulk and its suprathermal components, using Alfv{acute e}n Eigenmodes (AEs) excited by external antennas and by energetic particles. The measurements of AE frequencies and mode numbers give information on the bulk plasma. Improved equilibrium reconstruction, in particular in terms of radial profiles of density and safety factor, is possible from the comparison between the antenna driven spectrum and that calculated theoretically. Details of the time evolution of the non-monotonic safety factor profile in advanced scenarios can be reconstructed from the frequency of ICRH-driven energetic particle modes. The plasma effective mass can be inferred from the resonant frequency of externally driven AEs in discharges with similar equilibrium profiles. The stability thresholds and the nonlinear development of the instabilities can give clues on energy and spatial distribution of the fast particle population. The presence of unstable AEs provides lower limits in the energy of ICRH generated fast ion tails. Fast ion pressure gradients and their evolution can be inferred from the stability of AEs at different plasma radial positions. Finally, the details of the AE spectrum in the nonlinear stage can be used to obtain information about the fast particle velocity space diffusion.

  16. Output from MHD Models

    NASA Astrophysics Data System (ADS)

    Vlahakis, Nektarios

    2010-03-01

    Outflows emanating from the environment of stellar or galactic objects are a widespread phenomenon in astrophysics. Their morphology ranges from nearly spherically symmetric winds to highly collimated jets. In some cases, e.g., in jets associated with young stellar objects, the bulk outflow speeds are nonrelativistic, while in others, e.g., in jets associated with active galactic nuclei or gamma-ray bursts, it can even be highly relativistic. The main driving mechanism of collimated outflows is likely related to magnetic fields. These fields are able to tap the rotational energy of the compact object or disk, accelerate, and collimate matter ejecta. To zeroth order these outflows can be described by the highly intractable theory of magnetohydrodynamics (MHD). Even in systems where the assumptions of zero resistivity (ideal MHD), steady state, axisymmetry, one fluid description, and polytropic equation of state are applicable, the problem remains difficult. In this case the problem reduces to only two equations, corresponding to the two components of the momentum equation along the flow and in the direction perpendicular to the magnetic field (transfield direction). The latter equation is the most difficult to solve, but also the most important. It answers the question on the degree of the collimation, but also crucially affects the solution of the first, the acceleration efficiency and the bulk velocity of the flow. The first and second parts of this chapter refer to nonrelativistic and relativistic flows, respectively. These Parts can be read independently. In each one, the governing equations are presented and discussed, focusing on the case of flows that are magnetically dominated near the central source. The general characteristics of the solutions in relation to the acceleration and collimation mechanisms are analyzed. As specific examples of exact solutions of the full system of the MHD equations that satisfy all the analyzed general characteristics, self

  17. MHD Power Generation

    ERIC Educational Resources Information Center

    Kantrowitz, Arthur; Rosa, Richard J.

    1975-01-01

    Explains the operation of the Magnetohydrodynamic (MHD) generator and advantages of the system over coal, oil or nuclear powered generators. Details the development of MHD generators in the United States and Soviet Union. (CP)

  18. Modeling MHD Equilibrium and Dynamics with Non-Axisymmetric Resistive Walls in LTX and HBT-EP

    NASA Astrophysics Data System (ADS)

    Hansen, C.; Levesque, J.; Bialek, J.; Boyle, D. P.; Schmitt, J.

    2016-10-01

    In experimental magnetized plasmas, currents in the first wall, vacuum vessel, and other conducting structures can have a strong influence on plasma shape and dynamics. These effects are complicated by the 3D nature of these structures, which dictate available current paths. Results from simulations to study the effect of external currents on plasmas in two different experiments will be presented: 1) The arbitrary geometry, 3D extended MHD code PSI-Tet is applied to study linear and non-linear plasma dynamics in the High Beta Tokamak (HBT-EP) focusing on toroidal asymmetries in the adjustable conducting wall. 2) Equilibrium reconstructions of the Lithium Tokamak eXperiment (LTX) in the presence of non-axisymmetric eddy currents. An axisymmetric model is used to reconstruct the plasma equilibrium, using the PSI-Tri code, along with a set of fixed eddy current distributions. Current distributions are generated using 3D time-dependent, thin-wall, eddy current simulations using VALEN or PSI-Tet. Simulations of detailed experimental geometries are enabled by use of the PSI-Tet code, which employs a high order finite element method on unstructured tetrahedral grids that are generated directly from CAD models. Further development of PSI-Tet will also be presented. Work supported by US DOE.

  19. Electric fields, weighting fields, signals and charge diffusion in detectors including resistive materials

    NASA Astrophysics Data System (ADS)

    Riegler, W.

    2016-11-01

    In this report we discuss static and time dependent electric fields in detector geometries with an arbitrary number of parallel layers of a given permittivity and weak conductivity. We derive the Green's functions i.e. the field of a point charge, as well as the weighting fields for readout pads and readout strips in these geometries. The effect of `bulk' resistivity on electric fields and signals is investigated. The spreading of charge on thin resistive layers is also discussed in detail, and the conditions for allowing the effect to be described by the diffusion equation is discussed. We apply the results to derive fields and induced signals in Resistive Plate Chambers, MICROMEGAS detectors including resistive layers for charge spreading and discharge protection as well as detectors using resistive charge division readout like the MicroCAT detector. We also discuss in detail how resistive layers affect signal shapes and increase crosstalk between readout electrodes.

  20. Magnetohydrodynamic (MHD) channel corner seal

    DOEpatents

    Spurrier, Francis R.

    1980-01-01

    A corner seal for an MHD duct includes a compressible portion which contacts the duct walls and an insulating portion which contacts the electrodes, sidewall bars and insulators. The compressible portion may be a pneumatic or hydraulic gasket or an open-cell foam rubber. The insulating portion is segmented into a plurality of pieces of the same thickness as the electrodes, insulators and sidewall bars and aligned therewith, the pieces aligned with the insulator being of a different size from the pieces aligned with the electrodes and sidewall bars to create a stepped configuration along the corners of the MHD channel.

  1. Model for resistance evolution in shape memory alloys including R-phase

    NASA Astrophysics Data System (ADS)

    Brammajyosula, Ravindra; Buravalla, Vidyashankar; Khandelwal, Ashish

    2011-03-01

    The electrical resistance behavior of a shape memory alloy (SMA) wire can be used for sensing the state of an SMA device. Hence, this study investigates the resistance evolution in SMAs. A lumped parameter model with cosine kinetics to capture the resistance variation during the phase transformation is developed. Several SMA materials show the presence of trigonal or rhombohedral (R) phase as an intermediate phase, apart from the commonly recognized austenite and martensite phases. Most of the SMA models ignore the R-phase effect in their prediction of thermomechanical response. This may be acceptable since the changes in thermomechanical response associated with the R-phase are relatively less. However, the resistivity related effects are pronounced in the presence of the R-phase and its appearance introduces non-monotonicity in the resistivity evolution. This leads to additional complexities in the use of resistance signal for sensing and control. Hence, a lumped model is developed here for resistance evolution including the R-phase effects. A phase-diagram-based model is proposed for predicting electro-thermomechanical response. Both steady state hysteretic response and transient response are modeled. The model predictions are compared with the available test data. Numerical studies have shown that the model is able to capture all the essential features of the resistance evolution in SMAs in the presence of the R-phase.

  2. Cometary MHD and chemistry

    NASA Technical Reports Server (NTRS)

    Wegmann, R.; Schmidt, H. U.; Huebner, W. F.; Boice, D. C.

    1987-01-01

    An MHD and chemical comet-coma model was developed, applying the computer program of Huebner (1985) for the detailed chemical evolution of a spherically expanding coma and the program of Schmidt and Wegman (1982) and Wegman (1987) for the MHD flow of plasma and magnetic field in a comet to the Giotto-mission data on the ion abundances measured by the HIS ion mass spectrometer. The physics and chemistry of the coma are modeled in great detail, including photoprocesses, gas-phase chemical kinetics, energy balance with a separate electron temperature, multifluid hydrodynamics with a transition to free molecular flow, fast-streaming atomic and molecular hydrogen, counter and cross streaming of the ionized species relative to the neutral species in the coma-solar wind interaction region with momentum exchange by elastic collisions, mass-loading through ion pick-up, and Lorentz forces of the advected magnetic field. The results, both inside and outside of the contact surface, are discussed and compared with the relevant HIS ion mass spectra.

  3. Explosive MHD Generators

    NASA Astrophysics Data System (ADS)

    Lebedev, E. F.; Ostashev, V. E.; Fortov, V. E.

    2004-11-01

    Explosive driven MHD generators (EMHD) occupy an intermediate position between destroyed Explosive Flux Compression Generators and solid-propellant- pulsed MHD generators. Studies revealed the negative consequences of destroying a plasma liner through Rayleigh-Taylor instability. The real efficiency of conversion of condensed HE charge chemical energy reaches ~10% if the magnetic field in a MHD channel is approximately 8-10 T. Accommodation of 20-30 linear MHD channels into a toroidal magnet seems to be optimal for EMHD generator design. This device may operate repeatedly with a frequency of up to 6.5×103pps.

  4. Chemical solver to compute molecule and grain abundances and non-ideal MHD resistivities in prestellar core-collapse calculations

    NASA Astrophysics Data System (ADS)

    Marchand, P.; Masson, J.; Chabrier, G.; Hennebelle, P.; Commerçon, B.; Vaytet, N.

    2016-07-01

    We develop a detailed chemical network relevant to calculate the conditions that are characteristic of prestellar core collapse. We solve the system of time-dependent differential equations to calculate the equilibrium abundances of molecules and dust grains, with a size distribution given by size-bins for these latter. These abundances are used to compute the different non-ideal magneto-hydrodynamics resistivities (ambipolar, Ohmic and Hall), needed to carry out simulations of protostellar collapse. For the first time in this context, we take into account the evaporation of the grains, the thermal ionisation of potassium, sodium, and hydrogen at high temperature, and the thermionic emission of grains in the chemical network, and we explore the impact of various cosmic ray ionisation rates. All these processes significantly affect the non-ideal magneto-hydrodynamics resistivities, which will modify the dynamics of the collapse. Ambipolar diffusion and Hall effect dominate at low densities, up to nH = 1012 cm-3, after which Ohmic diffusion takes over. We find that the time-scale needed to reach chemical equilibrium is always shorter than the typical dynamical (free fall) one. This allows us to build a large, multi-dimensional multi-species equilibrium abundance table over a large temperature, density and ionisation rate ranges. This table, which we make accessible to the community, is used during first and second prestellar core collapse calculations to compute the non-ideal magneto-hydrodynamics resistivities, yielding a consistent dynamical-chemical description of this process. The multi-dimensional multi-species equilibrium abundance table and a copy of the code are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A18

  5. Lattice Boltzmann Representations of MHD Turbulence

    NASA Astrophysics Data System (ADS)

    Vahala, George; Vahala, Linda; Soe, Min; Flint, Christopher

    2013-10-01

    Lattice Botlzmann algorithms are an ideally parallelized method for the solutions of macroscopic nonlinear equations of physics - like resistive MHD. In its simplest LB representation one introduces a scalar distribution for the density-velocity fields and a vector distribution for the magnetic field. An important feature is that gradients of certain macroscopic fields can be represented by local moments of the mesoscopic distribution functions. In particular, div B = 0 can be exactly enforced to machine accuracy, without any divergence cleaning. One of the problems facing the explicit LB code is numerical instabilities. Methods to permit strong turbulence simulations include: (a) moving from a single BGK to multiple collisional relaxation, (b) quasi-equilibria and central moment enhanced LB representations. The LB turbulence modeling of Ansumali et al. to Navier-Stokes turbulence will be extended to MHD in which in its noted that filtering and Chapman-Enskog limits do not commute. In the NS-case, it leads to unique Samgorinsky closure scheme, with definite filter width.

  6. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-01-01

    The overall objective of the project is to design and construct prototypical hardware for an integrated MHD topping cycle, and conduct long duration proof-of-concept tests of integrated system at the US DOE Component Development and Integration Facility in Butte, Montana. The results of the long duration tests will augment the existing engineering design data base on MHD power train reliability, availability, maintainability, and performance, and will serve as a basis for scaling up the topping cycle design to the next level of development, an early commercial scale power plant retrofit. The components of the MHD power train to be designed, fabricated, and tested include: A slagging coal combustor with a rated capacity of 50 MW thermal input, capable of operation with an Eastern (Illinois {number sign}6) or Western (Montana Rosebud) coal, a segmented supersonic nozzle, a supersonic MHD channel capable of generating at least 1.5 MW of electrical power, a segmented supersonic diffuser section to interface the channel with existing facility quench and exhaust systems, a complete set of current control circuits for local diagonal current control along the channel, and a set of current consolidation circuits to interface the channel with the existing facility inverter.

  7. MHD Technology Transfer, Integration and Review Committee

    SciTech Connect

    Not Available

    1989-10-01

    As part of the MHD Integrated Topping Cycle (ITC) project, TRW was given the responsibility to organize, charter and co-chair, with the Department of Energy (DOE), an MHD Technology Transfer, Integration and Review Committee (TTIRC). The Charter of the TTIRC, which was approved by the DOE in June 1988 and distributed to the committee members, is included as part of this Summary. As stated in the Charter, the purpose of this committee is to: (1) review all Proof-of-Concept (POC) projects and schedules in the national MHD program; to assess their compatibility with each other and the first commercial MHD retrofit plant; (2) establish and implement technology transfer formats for users of this technology; (3) identify interfaces, issues, and funding structures directly impacting the success of the commercial retrofit; (4) investigate and identify the manner in which, and by whom, the above should be resolved; and (5) investigate and assess other participation (foreign and domestic) in the US MHD Program. The DOE fiscal year 1989 MHD Program Plan Schedule is included at the end of this Summary. The MHD Technology Transfer, Integration and Review Committee's activities to date have focused primarily on the technology transfer'' aspects of its charter. It has provided a forum for the dissemination of technical and programmatic information among workers in the field of MHD and to the potential end users, the utilities, by holding semi-annual meetings. The committee publishes this semi-annual report, which presents in Sections 2 through 11 capsule summaries of technical progress for all DOE Proof-of-Concept MHD contracts and major test facilities.

  8. Chapter 3: MHD stability, operational limits and disruptions

    NASA Astrophysics Data System (ADS)

    Hender, T. C.; Wesley, J. C.; Bialek, J.; Bondeson, A.; Boozer, A. H.; Buttery, R. J.; Garofalo, A.; Goodman, T. P.; Granetz, R. S.; Gribov, Y.; Gruber, O.; Gryaznevich, M.; Giruzzi, G.; Günter, S.; Hayashi, N.; Helander, P.; Hegna, C. C.; Howell, D. F.; Humphreys, D. A.; Huysmans, G. T. A.; Hyatt, A. W.; Isayama, A.; Jardin, S. C.; Kawano, Y.; Kellman, A.; Kessel, C.; Koslowski, H. R.; La Haye, R. J.; Lazzaro, E.; Liu, Y. Q.; Lukash, V.; Manickam, J.; Medvedev, S.; Mertens, V.; Mirnov, S. V.; Nakamura, Y.; Navratil, G.; Okabayashi, M.; Ozeki, T.; Paccagnella, R.; Pautasso, G.; Porcelli, F.; Pustovitov, V. D.; Riccardo, V.; Sato, M.; Sauter, O.; Schaffer, M. J.; Shimada, M.; Sonato, P.; Strait, E. J.; Sugihara, M.; Takechi, M.; Turnbull, A. D.; Westerhof, E.; Whyte, D. G.; Yoshino, R.; Zohm, H.; ITPA MHD, the; Disruption; Magnetic Control Topical Group

    2007-06-01

    Progress in the area of MHD stability and disruptions, since the publication of the 1999 ITER Physics Basis document (1999 Nucl. Fusion 39 2137-2664), is reviewed. Recent theoretical and experimental research has made important advances in both understanding and control of MHD stability in tokamak plasmas. Sawteeth are anticipated in the ITER baseline ELMy H-mode scenario, but the tools exist to avoid or control them through localized current drive or fast ion generation. Active control of other MHD instabilities will most likely be also required in ITER. Extrapolation from existing experiments indicates that stabilization of neoclassical tearing modes by highly localized feedback-controlled current drive should be possible in ITER. Resistive wall modes are a key issue for advanced scenarios, but again, existing experiments indicate that these modes can be stabilized by a combination of plasma rotation and direct feedback control with non-axisymmetric coils. Reduction of error fields is a requirement for avoiding non-rotating magnetic island formation and for maintaining plasma rotation to help stabilize resistive wall modes. Recent experiments have shown the feasibility of reducing error fields to an acceptable level by means of non-axisymmetric coils, possibly controlled by feedback. The MHD stability limits associated with advanced scenarios are becoming well understood theoretically, and can be extended by tailoring of the pressure and current density profiles as well as by other techniques mentioned here. There have been significant advances also in the control of disruptions, most notably by injection of massive quantities of gas, leading to reduced halo current fractions and a larger fraction of the total thermal and magnetic energy dissipated by radiation. These advances in disruption control are supported by the development of means to predict impending disruption, most notably using neural networks. In addition to these advances in means to control or

  9. Finite difference time domain electroacoustic model for synthetic jet actuators including nonlinear flow resistance.

    PubMed

    Kooijman, Gerben; Ouweltjes, Okke

    2009-04-01

    A lumped element electroacoustic model for a synthetic jet actuator is presented. The model includes the nonlinear flow resistance associated with flow separation and employs a finite difference scheme in the time domain. As opposed to more common analytical frequency domain electroacoustic models, in which the nonlinear resistance can only be considered as a constant, it allows the calculation of higher harmonics, i.e., distortion components, generated as a result of this nonlinear resistance. Model calculations for the time-averaged momentum flux of the synthetic jet as well as the radiated sound power spectrum are compared to experimental results for various configurations. It is shown that a significantly improved prediction of the momentum flux-and thus flow velocity-of the jet is obtained when including the nonlinear resistance. Here, the current model performs slightly better than an analytical model. For the power spectrum of radiated sound, a reasonable agreement is obtained when assuming a plausible slight asymmetry in the nonlinear resistance. However, results suggest that loudspeaker nonlinearities play a significant role as well in the generation of the first few higher harmonics.

  10. MHD Turbulence and Magnetic Dynamos

    NASA Technical Reports Server (NTRS)

    Shebalin, John V

    2014-01-01

    Incompressible magnetohydrodynamic (MHD) turbulence and magnetic dynamos, which occur in magnetofluids with large fluid and magnetic Reynolds numbers, will be discussed. When Reynolds numbers are large and energy decays slowly, the distribution of energy with respect to length scale becomes quasi-stationary and MHD turbulence can be described statistically. In the limit of infinite Reynolds numbers, viscosity and resistivity become zero and if these values are used in the MHD equations ab initio, a model system called ideal MHD turbulence results. This model system is typically confined in simple geometries with some form of homogeneous boundary conditions, allowing for velocity and magnetic field to be represented by orthogonal function expansions. One advantage to this is that the coefficients of the expansions form a set of nonlinearly interacting variables whose behavior can be described by equilibrium statistical mechanics, i.e., by a canonical ensemble theory based on the global invariants (energy, cross helicity and magnetic helicity) of ideal MHD turbulence. Another advantage is that truncated expansions provide a finite dynamical system whose time evolution can be numerically simulated to test the predictions of the associated statistical mechanics. If ensemble predictions are the same as time averages, then the system is said to be ergodic; if not, the system is nonergodic. Although it had been implicitly assumed in the early days of ideal MHD statistical theory development that these finite dynamical systems were ergodic, numerical simulations provided sufficient evidence that they were, in fact, nonergodic. Specifically, while canonical ensemble theory predicted that expansion coefficients would be (i) zero-mean random variables with (ii) energy that decreased with length scale, it was found that although (ii) was correct, (i) was not and the expected ergodicity was broken. The exact cause of this broken ergodicity was explained, after much

  11. Magnetic reconnection in a compressible MHD plasma

    SciTech Connect

    Hesse, Michael; Zenitani, Seiji; Birn, Joachim

    2011-04-15

    Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed.

  12. Magnetic Reconnection in a Compressible MHD Plasma

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Zenitani, Seiji

    2011-01-01

    Using steady-state resistive MHD, magnetic reconnection is reinvestigated for conditions of high resistivity/low magnetic Reynolds number, when the thickness of the diffusion region is no longer small compared to its length. Implicit expressions for the reconnection rate and other reconnection parameters are derived based on the requirements of mass, momentum, and energy conservation. These expressions are solved via simple iterative procedures. Implications specifically for low Reynolds number/high resistivity are being discussed

  13. Salient issues of edge physics pertaining to loss of confinement: A resistive MHD analysis. Technical progress report, FY91

    SciTech Connect

    Thayer, D.R.

    1991-12-31

    The progress that has been made during this fiscal year is significant in the area of tokamak edge plasma transport. Important contributions on the extension of the drift-rippling mode model ({approximately} {tau}, {approximately}n, {approximately}T, {approximately}{nu}{sub {parallel}}) of edge turbulent transport. In particular, the research areas on which we have concentrated include the following topics: (1) The theoretical investigation of the radiatively enhanced transport due to the effects of impurity driven radiation instabilities has been expanded to include a situation with multiple impurities (such as carbon, C{sup 4+}, and oxygen, O{sup 6+}); (2) In order to validate the use of the impurity radiation input from the tokamak bolometer experiments in our theoretical edge turbulent transport calculations, the analysis that is utilized to transform impurity brightness data to radiated power profiles has been checked for state population and Abel inversion correctness; (3) The drift-rippling model of edge turbulent transport has been extended to include ionization particle sources in addition to the impurity driven thermal instability drive; and (4) The detailed limiter and realistic edge geometric effects on the edge turbulent transport has been included in the drift-rippling model.

  14. Salient issues of edge physics pertaining to loss of confinement: A resistive MHD analysis. FY91 technical progress report

    SciTech Connect

    Thayer, D.R.

    1991-12-31

    The progress that has been made during this fiscal year is significant in the area of tokamak edge plasma transport. The drift-rippling mode model of edge turbulent transport was extended. In particular, the research areas on which were concentrated include the following topics: (1) The theoretical investigation of the radiatively enhanced transport due to the effects of impurity driven radiation instabilities has been expanded to include a situation with multiple impurities (such as carbon, C{sup 4+}, and oxygen, O{sup 6+}); (2) In order to validate the use of the impurity radiation input from the tokamak bolometer experiments in the theoretical edge turbulent transport calculations, the analysis that is utilized to transform impurity brightness data to radiated power profiles has been checked for state population and Abel inversion correctness; (3) The drift-rippling model of edge turbulent transport has been extended to include ionization particle sources in addition to the impurity driven thermal instability drive; and (4) The detailed limiter and realistic edge geometric effects on the edge turbulent transport has been included in the drift-rippling model.

  15. HYBRID AND HALL-MHD SIMULATIONS OF COLLISIONLESS RECONNECTION: EFFECTS OF PLASMA PRESSURE TENSOR

    SciTech Connect

    L. YIN; D. WINSKE; ET AL

    2001-05-01

    In this study we performed two-dimensional hybrid (particle ions, massless fluid electrons) and Hall-MHD simulations of collisionless reconnection in a thin current sheet. Both calculations include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and in both an initial perturbation to the Harris equilibrium is applied. First, electron dynamics from the two calculations are compared, and we find overall agreement between the two calculations in both the reconnection rate and the global configuration. To address the issue of how kinetic treatment for the ions affects the reconnection dynamics, we compared the fluid-ion dynamics from the Hall-MHD calculation to the particle-ion dynamics obtained from the hybrid simulation. The comparison demonstrates that off-diagonal elements of the ion pressure tensor are important in correctly modeling the ion out-of-plane momentum transport from the X point. It is that these effects can be modeled efficiently using a particle Hall-MHD simulation method in which particle ions used in a predictor/corrector to implement the ion gyro-radius corrections. We also investigate the micro- macro-scale coupling in the magnetotail dynamics by using a new integrated approach in which particle Hall-MHD calculations are embedded inside a MHD simulation. Initial results of the simulation concerning current sheet thinning and reconnection dynamics are discussed.

  16. Open Boundary Conditions for Dissipative MHD

    SciTech Connect

    Meier, E T

    2011-11-10

    In modeling magnetic confinement, astrophysics, and plasma propulsion, representing the entire physical domain is often difficult or impossible, and artificial, or 'open' boundaries are appropriate. A novel open boundary condition (BC) for dissipative MHD, called Lacuna-based open BC (LOBC), is presented. LOBC, based on the idea of lacuna-based truncation originally presented by V.S. Ryaben'kii and S.V. Tsynkov, provide truncation with low numerical noise and minimal reflections. For hyperbolic systems, characteristic-based BC (CBC) exist for separating the solution into outgoing and incoming parts. In the hyperbolic-parabolic dissipative MHD system, such separation is not possible, and CBC are numerically unstable. LOBC are applied in dissipative MHD test problems including a translating FRC, and coaxial-electrode plasma acceleration. Solution quality is compared to solutions using CBC and zero-normal derivative BC. LOBC are a promising new open BC option for dissipative MHD.

  17. Hall MHD in the Magnetopause with OpenGGCM

    NASA Astrophysics Data System (ADS)

    Maynard, K. R. M.; Germaschewski, K.; Lin, L.; Raeder, J.

    2014-12-01

    Dayside magnetic reconnection plays a major role in the global dynamics of the magnetosphere as it interacts with the solar wind. Global MHD simulations typically use finite resistivity to mediate reconnection; however, in realistic parameters, resistive scales are significantly smaller than ion scales. Previously, 2-D studies have shown that including ion scale physics through the Hall term in the generalized Ohm's law can dramatically alter dynamics and reconnection rates when compared with resistive MHD models. In this study, we use OpenGGCM to investigate magnetopause reconnection at high Lundquist numbers with synthetic solar wind conditions. OpenGGCM has recently been extended to include a van-Leer constrained-transport numerical scheme (Stone 2008) similar to that used in the Athena code. We compare global simulations with asymmetric 2-D cases where, unlike in the magnetopause, flux tubes are not free to advect around the diffusion region. We also show how the Hall term affects the structure of flux transfer events.

  18. Drug-resistant tuberculosis in subjects included in the Second National Survey on Antituberculosis Drug Resistance in Porto Alegre, Brazil*, **

    PubMed Central

    Micheletti, Vania Celina Dezoti; Moreira, José da Silva; Ribeiro, Marta Osório; Kritski, Afranio Lineu; Braga, José Ueleres

    2014-01-01

    OBJECTIVE: To describe the prevalence of multidrug-resistant tuberculosis (MDR-TB) among tuberculosis patients in a major Brazilian city, evaluated via the Second National Survey on Antituberculosis Drug Resistance, as well as the social, demographic, and clinical characteristics of those patients. METHODS: Clinical samples were collected from tuberculosis patients seen between 2006 to 2007 at three hospitals and five primary health care clinics participating in the survey in the city of Porto Alegre, Brazil. The samples were subjected to drug susceptibility testing. The species of mycobacteria was confirmed using biochemical methods. RESULTS: Of the 299 patients included, 221 (73.9%) were men and 77 (27.3%) had a history of tuberculosis. The mean age was 36 years. Of the 252 patients who underwent HIV testing, 66 (26.2%) tested positive. The prevalence of MDR-TB in the sample as a whole was 4.7% (95% CI: 2.3-7.1), whereas it was 2.2% (95% CI: 0.3-4.2) among the new cases of tuberculosis and 12.0% (95% CI: 4.5-19.5) among the patients with a history of tuberculosis treatment. The multivariate analysis showed that a history of tuberculosis and a longer time to diagnosis were both associated with MDR-TB. CONCLUSIONS: If our results are corroborated by other studies conducted in Brazil, a history of tuberculosis treatment and a longer time to diagnosis could be used as predictors of MDR-TB. PMID:24831400

  19. 2-D MHD numerical simulations of EML plasma armatures with ablation

    NASA Astrophysics Data System (ADS)

    Boynton, G. C.; Huerta, M. A.; Thio, Y. C.

    1993-01-01

    We use a 2-D) resistive MHD code to simulate an EML plasma armature. The energy equation includes Ohmic heating, radiation heat transport and the ideal gas equation of state, allowing for variable ionization using the Saha equations. We calculate rail ablation taking into account the flow of heat into the interior of the rails. Our simulations show the development of internal convective flows and secondary arcs. We use an explicit Flux Corrected Transport algorithm to advance all quantities in time.

  20. Computation of the MHD modes with rotation and kinetic effects: AEGIS

    NASA Astrophysics Data System (ADS)

    Zheng, L.-J.; Kotschenreuther, M.; Turnbull, A.; Waelbroeck, F.; van Dam, J. W.; Berk, H.

    2003-10-01

    A new linear MHD eigenvalue code called AEGIS (Adaptive EiGenfunction Independent Shooting) is being developed at the IFS. The benchmarking of AEGIS with GATO is underway and will be presented. Plasma rotation is being included, with the effect of rotation-enhanced plasma compressibility also taken into account. As a first step in including rotational effects, the ideal MHD model is being employed. Details of the numerical scheme will be described, along with preliminary numerical results. The plan to include kinetic compressiblity will be discussed. With this new code, rotational stabilization of resistive wall modes can be rigorously calculated for the first time. The algorithm also allows FLR effects to be included. Many helpful suggestions from A. Glasser are acknowledged.

  1. Analytic expression for the Fowler-Nordheim V- I characteristic including the series resistance effect

    NASA Astrophysics Data System (ADS)

    Miranda, E.; Palumbo, F.

    2011-07-01

    It is shown in this communication that the Fowler-Nordheim (FN) tunneling expression for the current-voltage ( I- V) characteristic can be analytically inverted so that an exact expression for the voltage-current ( V- I) characteristic can be obtained. The solution of the resulting implicit equation is found using the Lambert W function, i.e. the solution of the transcendental equation we w = x. The reported expressions are supported by experimental I- V curves measured in thin (≈5 nm) SiO 2 films in MOS capacitors. The analysis includes the case of a tunneling oxide with a large series resistance. For practical purposes, a closed-form expression for W based on a Padé-type approximation is also provided.

  2. MHD Equation of State with Relativistic Electrons

    NASA Astrophysics Data System (ADS)

    Gong, Zhigang; Däppen, Werner; Zejda, Ladislav

    2001-01-01

    The Mihalas-Däppen-Hummer (MHD) equation of state does not include the effect of relativistic partially degenerate electrons, although nonrelativistic partial degeneracy is taken into account. The discovery of a relativistic correction in helioseismology forces us to perform an appropriate upgrade of the MHD equation of state. We have adopted the method of J. M. Aparicio to evaluate the relativistic Fermi-Dirac functions. Our calculations confirm the validity of the approximation used, which works well for the weakly relativistic electrons under solar-center conditions. However, our results will also provide reliable thermodynamic quantities in the stronger relativistic regime as found in more massive stars. Since a particular feature of the original MHD papers was an explicit list of the adopted free energy and its first- and second-order analytical derivatives, we give the corresponding relativistic quantities in the Appendix.

  3. Disk MHD generator study

    NASA Technical Reports Server (NTRS)

    Retallick, F. D.

    1980-01-01

    Directly-fired, separately-fired, and oxygen-augmented MHD power plants incorporating a disk geometry for the MHD generator were studied. The base parameters defined for four near-optimum-performance MHD steam power systems of various types are presented. The finally selected systems consisted of (1) two directly fired cases, one at 1920 K (2996F) preheat and the other at 1650 K (2500 F) preheat, (2) a separately-fired case where the air is preheated to the same level as the higher temperature directly-fired cases, and (3) an oxygen augmented case with the same generator inlet temperature of 2839 (4650F) as the high temperature directly-fired and separately-fired cases. Supersonic Mach numbers at the generator inlet, gas inlet swirl, and constant Hall field operation were specified based on disk generator optimization. System pressures were based on optimization of MHD net power. Supercritical reheat stream plants were used in all cases. Open and closed cycle component costs are summarized and compared.

  4. Analytical estimates of turbulent MHD transport coefficients

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Hatori, T.

    1984-01-01

    Turbulent transfer rates from small-scale MHD excitations to large-scale Fourier modes are calculated algebraically, using the method of Biskamp and Welter. Three cases are considered: two-dimensional Navier-Stokes flows, two-dimensional incompressible MHD, and the weakly three-dimensional Strauss equations. In all cases, an initially large spectral gap between the small-scale and large-scale excitations is assumed, and attention focusses on the initial values of the back-transfer rates. The sign of the transfer is determined by the sign of an analytically calculable eddy viscosity and/or anomalous resistivity. We are able to confirm the results of Biskamp and Welter for the case of two-dimensional MHD, but find some differences for the case of the Strauss equations. It is argued that the Strauss equations may not exhibit an inverse cascade phenomenon for the spatially periodic case unless their initial spectra are such that the behavior is essentially that of two-dimensional MHD.

  5. Hospital Isolates of Serratia marcescens Transferring Ampicillin, Carbenicillin, and Gentamicin Resistance to Other Gram-Negative Bacteria Including Pseudomonas aeruginosa

    PubMed Central

    Olexy, Vera M.; Bird, Thomas J.; Grieble, Hans G.; Farrand, Stephen K.

    1979-01-01

    Thirteen independent isolates of Serratia marcescens associated with nosocomial urinary tract infections were obtained from the clinical microbiology laboratory at Hines Veterans Administration Hospital. The isolates were resistant to at least ampicillin, carbenicillin, gentamicin, and tobramycin. They could be divided into two groups on the basis of their antibiotypes. Group I (9 strains) showed resistance to 13 antibiotics, including 3 beta-lactams, 6 aminoglycosides, tetracycline, sulfonamide, trimethoprim, and polymyxin B. Group II (4 strains) was resistant to 11 antibiotics, including 3 beta-lactams, 5 aminoglycosides, sulfonamide, trimethoprim, and polymyxin B. Donors from both groups transferred resistance traits to Escherichia coli. Transconjugants from matings with group II donors all acquired resistance to nine antibiotics, including the three beta-lactams, five aminoglycosides, and sulfonamide. Transconjugants from matings with group I donors were of varied antibiotypes, inheriting resistance to up to 11 of the 13 antibiotics. Resistances to trimethoprim and polymyxin B were never observed to transfer. E. coli transconjugants of each group were capable of transferring multiple-antibiotic resistance to several other members of the family Enterobacteriaceae. All group II S. marcescens and E. coli donors and all group I S. marcescens donors transferred carbenicillin, streptomycin, kanamycin, gentamicin, tobramycin, and sisomicin resistance to Pseudomonas aeruginosa. The results suggest that these S. marcescens strains harbor R factors of a broader host range than previously reported. PMID:106772

  6. MHD simulations: Corotating Interaction Regions

    NASA Astrophysics Data System (ADS)

    Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kühl, P.; Heber, B.; Kissmann, R.

    2013-12-01

    Corotating Interaction Regions (CIRs) form in the solar wind when parcels of fast-speed wind interact with slow-speed wind due to the rotation of the Sun. The resulting buildup of pressure generates disturbances that, with increasing time (or distance from the Sun), may develop into a so-called forward-reverse shock-pair. During solar-quiet times CIRs can be the dominant force shaping large-scale structures in the heliosphere. Studying CIRs is therefore important because the associated shocks are capable of e.g. accelerating energetic particles or deflecting cosmic rays. The global structure of CIRs can be modeled with an MHD approach that gives the plasma quantities needed to model the transport of particles in the heliosphere (with e.g. stochastic differential equations (SDEs)). Our MHD code CRONOS employs a semi-discrete finite volume scheme with adaptive time-stepping Runge-Kutta integration. The solenoidality of the magnetic field is ensured via constrained transport and the code supports Cartesian, Cylindrical and Spherical coordinates (including coordinate singularities) with the option for non-equidistant grids. The code runs in parallel (MPI) and supports the HDF5 output data format. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations. Comparison with Pizzo (1982) for analytic boundary conditions Comparison with STEREO A for Carrington Rotation 2060

  7. The role of kinetic effects, including plasma rotation and energetic particles, in resistive wall mode stability

    SciTech Connect

    Berkery, J. W.; Sabbagh, S. A.; Reimerdes, H.; Betti, R.; Hu, B.; Bell, R. E.; Gerhardt, S. P.; Manickam, J.; Podesta, M.

    2010-08-15

    The resistive wall mode (RWM) instability in high-beta tokamaks is stabilized by energy dissipation mechanisms that depend on plasma rotation and kinetic effects. Kinetic modification of ideal stability calculated with the 'MISK' code [B. Hu et al., Phys. Plasmas 12, 057301 (2005)] is outlined. For an advanced scenario ITER [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)] plasma, the present calculation finds that alpha particles are required for RWM stability at presently expected levels of plasma rotation. Kinetic stabilization theory is tested in an experiment in the National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] that produced marginally stable plasmas with various energetic particle contents. Plasmas with the highest and lowest energetic particle content agree with calculations predicting that increased energetic particle pressure is stabilizing but does not alter the nonmonotonic dependence of stability on plasma rotation due to thermal particle resonances. Presently, the full MISK model, including thermal particles and an isotropic slowing-down distribution function for energetic particles, overpredicts stability in NSTX experiments. Minor alteration of either effect in the theory may yield agreement; several possibilities are discussed.

  8. Isolation of Clostridium difficile from dogs with digestive disorders, including stable metronidazole-resistant strains.

    PubMed

    Orden, Cristina; Blanco, Jose L; Álvarez-Pérez, Sergio; Garcia-Sancho, Mercedes; Rodriguez-Franco, Fernando; Sainz, Angel; Villaescusa, Alejandra; Harmanus, Celine; Kuijper, Ed; Garcia, Marta E

    2017-02-01

    The prevalence of Clostridium difficile in 107 dogs with diverse digestive disorders attended in a Spanish veterinary teaching hospital was assessed. The microorganism was isolated from 13 dogs (12.1%) of different disease groups. Isolates belonged to PCR ribotypes 078, 106, 154 and 430 (all of them toxigenic) and 110 (non-toxigenic), and were resistant to several antimicrobial drugs. Notably, seven isolates obtained from different dogs displayed stable resistance to metronidazole. The results of this study provide further evidence that dogs can act as a reservoir of C. difficile strains of epidemic ribotypes with resistance to multiple antibiotics.

  9. Synergy of Penicillin-Netilmicin Combinations Against Enterococci Including Strains Highly Resistant to Streptomycin or Kanamycin

    PubMed Central

    Sanders, Christine C.

    1977-01-01

    The in vitro activity of combinations of penicillin and netilimicin was determined against 20 clinical isolates of enterococci and compared with that obtained in simultaneous tests with penicillin/sisomicin, penicillin/streptomycin, and penicillin/kanamycin. Synergy between the two drugs in each combination was determined by the use of quantitative kill curves and was defined as a killing by the combination at least 100-fold greater than that produced by the most effective drug alone. Penicillin/netilmicin and penicillin/sisomicin combinations were found to be synergistic against the majority of isolates tested, including strains resistant to penicillin/streptomycin or penicillin/kanamycin combinations. This synergy with penicillin could be demonstrated at a concentration of ≤7 μg/ml for either netilmicin or sisomicin. Studies on the kinetics of killing produced by these combinations showed the rate and extent of killing to be directly dependent upon the organism's relative susceptibility to the aminoglycoside alone and the aminoglycoside concentration in the combination. Results also indicated that the interaction between penicillin and netilmicin was true synergy; i.e., rapid and complete killing was produced by combinations containing each drug at concentrations insufficient to produce any killing alone, and the killing observed could not be produced by either drug alone at a concentration equivalent to the total drug concentration in the combination. The potential clinical application of this synergistic interaction should be investigated further, especially in view of recent reports showing netilmicin to be considerably less toxic than gentamicin in experimental animals. PMID:242509

  10. MHD Flow Control

    DTIC Science & Technology

    2006-09-01

    Plasmatron // The 15th International Conference on 16 N I MHD Energy Conversion and the 6th International Workshop on MagnetoPlasma Aerodynamics, IVTAN...series. 1 2. FACILITY The principal scheme of High Frequency Plasmatron is given in Fig.88, and basic specifications in the Table 1. The high-frequency...CHAMBER OF HF- PLASMATRON Statement of the problem Detailed diagnostics of plasma jet flow is required for any type of studies in HF- plasmatron . Gas flow in

  11. Advances in the theory and application of BSF cells. [including electrical resistivity and photovoltaic cells

    NASA Technical Reports Server (NTRS)

    Mandelkorn, J.; Lamneck, J. H.

    1975-01-01

    The characteristics and behavior of p(+), p solar cells were investigated. The p(+), p cells were made by the removal of the n(+) surface layers from n(+), p p(+), BSF cells followed by application of a suitable contact to the resultant p(+), p structures. The open circuit voltage of p(+), p cells was found to increase with increasing 'p' bulk resistivity. The measured open circuit velocity-temperature coefficients were positive and increased with increasing resistivity. An outline of prior limitations in solar cell design is presented, and the removal of these limitations through use of BSF effects is pointed out. The study of BSF effects made feasible production of very thin high efficiency silicon cells as well as high resistivity-high efficiency cells, two desirable types of silicon cells which were previously impossible to make.

  12. Improvement of Scratch and Wear Resistance of Polymers by Fillers Including Nanofillers

    PubMed Central

    Brostow, Witold; Lobland, Haley E. Hagg; Hnatchuk, Nathalie; Perez, Jose M.

    2017-01-01

    Polymers have lower resistance to scratching and wear than metals. Liquid lubricants work well for metals but not for polymers nor for polymer-based composites (PBCs). We review approaches for improvement of tribological properties of polymers based on inclusion of fillers. The fillers can be metallic or ceramic—with obvious consequences for electrical resistivity of the composites. Distinctions between effectiveness of micro- versus nano-particles are analyzed. For example, aluminum nanoparticles as filler are more effective for property improvement than microparticles at the same overall volumetric concentration. Prevention of local agglomeration of filler particles is discussed along with a technique to verify the prevention. PMID:28336900

  13. Improvement of Scratch and Wear Resistance of Polymers by Fillers Including Nanofillers.

    PubMed

    Brostow, Witold; Lobland, Haley E Hagg; Hnatchuk, Nathalie; Perez, Jose M

    2017-03-16

    Polymers have lower resistance to scratching and wear than metals. Liquid lubricants work well for metals but not for polymers nor for polymer-based composites (PBCs). We review approaches for improvement of tribological properties of polymers based on inclusion of fillers. The fillers can be metallic or ceramic-with obvious consequences for electrical resistivity of the composites. Distinctions between effectiveness of micro- versus nano-particles are analyzed. For example, aluminum nanoparticles as filler are more effective for property improvement than microparticles at the same overall volumetric concentration. Prevention of local agglomeration of filler particles is discussed along with a technique to verify the prevention.

  14. Classical MHD shocks: theory and numerical simulation

    SciTech Connect

    Pogorelov, Nikolai V.

    2005-08-01

    Recent results are surveyed in the investigation of the behavior of shocks in ideal magnetohydrodynamics (MHD) and corresponding structures in dissipative/resistive plasma flows. In contrast to evolutionary shocks, a solution of the problem of the nonevolutionary shock interaction with small perturbations is either nonunique or does not exist. The peculiarity of non-ideal MHD is in that some nonevolutionary shocks have dissipative structures. Since this structure is always non-plane, it can reveal itself in problems where transverse perturbations do not exist due to symmetries restrictions. We discuss the numerical behavior of nonevolutionary shocks and argue that they necessarily disappear once the problem is solved in a genuinely three-dimensional statement.

  15. Multiplex characterization of human pathogens including species and antibiotic-resistance gene identification.

    PubMed

    Barisˇ ić, Ivan; Petzka, Josefine; Schoenthaler, Silvia; Vierlinger, Klemens; Noehammer, Christa; Wiesinger-Mayr, Herbert

    2016-01-01

    The efficient medical treatment of infections requires detailed information about the pathogens involved and potential antibiotic-resistance mechanisms. The dramatically increasing incidence of multidrug-resistant bacteria especially highlights the importance of sophisticated diagnostic tests enabling a fast patient-customized therapy. However, the current molecular detection methods are limited to either the detection of species or only a few antibiotic-resistance genes.In this work, we present a human pathogen characterization assay using a rRNA gene microarray identifying 75 species comprising bacteria and fungi. A statistical classifier was developed to facilitate the automated species identification. Additionally, the clinically most important β-lactamases were identified simultaneously in a 100-plex reaction using padlock probes and the same microarray. The specificity and sensitivity of the combined assay was determined using clinical isolates. The detection limit was 10(5) c.f.u. ml(-1), recovering 89 % of the detectable β-lactamase-encoding genes specifically. The total assay time was less than 7 hand the modular character of the antibiotic-resistance detection allows the easy integration of further genetic targets. In summary, we present a fast, highly specific and sensitive multiplex pathogen characterization assay.

  16. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-07-01

    This seventeenth quarterly technical progress report of the MHD Integrated Topping Cycle Project presents the accomplishments during the period August 1, 1991 to October 31, 1991. Manufacturing of the prototypical combustor pressure shell has been completed including leak, proof, and assembly fit checking. Manufacturing of forty-five cooling panels was also completed including leak, proof, and flow testing. All precombustor internal components (combustion can baffle and swirl box) were received and checked, and integration of the components was initiated. A decision was made regarding the primary and backup designs for the 1A4 channel. The assembly of the channel related prototypical hardware continued. The cathode wall electrical wiring is now complete. The mechanical design of the diffuser has been completed.

  17. Cosmological AMR MHD with Enzo

    SciTech Connect

    Xu, Hao; Li, Hui; Li, Shengtai

    2009-01-01

    In this work, we present EnzoMHD, the extension of the cosmological code Enzoto include magnetic fields. We use the hyperbolic solver of Li et al. (2008) for the computation of interface fluxes. We use constrained transport methods of Balsara & Spicer (1999) and Gardiner & Stone (2005) to advance the induction equation, the reconstruction technique of Balsara (2001) to extend the Adaptive Mesh Refinement of Berger & Colella (1989) already used in Enzo, though formulated in a slightly different way for ease of implementation. This combination of methods preserves the divergence of the magnetic field to machine precision. We use operator splitting to include gravity and cosmological expansion. We then present a series of cosmological and non cosmologjcal tests problems to demonstrate the quality of solution resulting from this combination of solvers.

  18. MHD Wave Modes Resolved in Fine-Scale Chromospheric Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Verth, G.; Jess, D. B.

    2016-02-01

    Due to its complex and dynamic fine-scale structure, the chromosphere is a particularly challenging region of the Sun's atmosphere to understand. It is now widely accepted that to model chromospheric dynamics, even on a magnetohydrodynamic (MHD) scale, while also calculating spectral line emission, one must realistically include the effects of partial ionization and radiative transfer in a multi-fluid plasma under non-LTE conditions. Accurate quantification of MHD wave energetics must be founded on a precise identification of the actual wave mode being observed. This chapter focuses on MHD kink-mode identification, MHD sausage mode identification, and MHD torsional Alfvén wave identification. It then reviews progress in determining more accurate energy flux estimations of specific MHD wave modes observed in the chromosphere. The chapter finally examines how the discovery of these MHD wave modes has helped us advance the field of chromospheric magnetoseismology.

  19. Proteomic and metabolic analyses of early berry development in Vitis spp. including the period of ontogenic gain of resistance

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Early development of grape berries is marked by several biological changes, including cell division and expansion, as berries initiate double sigmoid growth. In most genotypes, a significant gain of ontogenic resistance (OR) to some pathogens, including powdery mildew (PM) (Uncinula necator), also o...

  20. Including dietary fiber and resistant starch to increase satiety and reduce aggression in gestating sows.

    PubMed

    Sapkota, A; Marchant-Forde, J N; Richert, B T; Lay, D C

    2016-05-01

    Aggression during mixing of pregnant sows impacts sow welfare and productivity. The aim of this study was to increase satiety and reduce aggression by including dietary fiber and fermentable carbohydrates. Sows were housed in individual stalls 7 to 14 d after breeding (moving day was considered d 0 of treatment) and were fed (at 0700 h) with a CONTROL (corn-soybean meal based with no additional fiber sources), RSTARCH (10.8% resistant starch), BEETPULP (27.2% sugar beet pulp), SOYHULLS (19.1% soybean hulls), or INCSOY (14.05% soybean hulls) for 21 d (5 sows/diet × 5 diets × 8 replications = 200 sows). The CONTROL diet was targeted to contain 185 g(d∙sow) NDF and the other diets were targeted to contain 350 g(d∙sow) NDF. The INCSOY diet was fed at 2.2 kg/(d∙sow) and the other diets were fed at 2 kg(d∙sow). On d 22, sows were mixed in groups of 5 (at 1200 h). Behaviors in stalls (on d 1, 7, 14, and 21) and after mixing (d 22 and 23), heart rate (on d 1, 7, 14, and 21), blood metabolites (on d 2, 8, 15, 22, and 25), and the effects of diets on production were collected and analyzed. Sows stood more ( < 0.01) and rested less ( < 0.001) over time irrespective of the diet. Sows on BEETPULP stood more ( < 0.01) and sows on SOYHULLS rested more ( < 0.01). Sham chewing increased over days irrespective of the diet. Chewing behavior (bar and feeder) increased with days on diet ( < 0.001) and was lowest in sows on the SOYHULLS diet ( = 0.045). When mixed, biting frequency in the first hour was highest for sows on the CONTROL diet (236.5 ± 62.6) and lowest for sows on the RSTARCH diet (90.5 ± 30.5). Skin lesions increased ( < 0.001) 24 h after mixing sows irrespective of diet. Blood urea nitrogen (BUN) concentration was lowest in sows fed BEETPULP and SOYHULLS ( < 0.001). Serum glucose concentration was highest in sows fed RSTARCH and BEETPULP ( = 0.04), but there was no day effect ( = 0.62) or diet × day interaction ( = 0.60). The NEFA was greatest in sows fed

  1. Fine-mapping diabetes-related traits, including insulin resistance, in heterogeneous stock rats.

    PubMed

    Solberg Woods, Leah C; Holl, Katie L; Oreper, Daniel; Xie, Yuying; Tsaih, Shirng-Wern; Valdar, William

    2012-11-01

    Type 2 diabetes (T2D) is a disease of relative insulin deficiency resulting from both insulin resistance and beta cell failure. We have previously used heterogeneous stock (HS) rats to fine-map a locus for glucose tolerance. We show here that glucose intolerance in the founder strains of the HS colony is mediated by different mechanisms: insulin resistance in WKY and an insulin secretion defect in ACI, and we demonstrate a high degree of variability for measures of insulin resistance and insulin secretion in HS rats. As such, our goal was to use HS rats to fine-map several diabetes-related traits within a region on rat chromosome 1. We measured blood glucose and plasma insulin levels after a glucose tolerance test in 782 male HS rats. Using 97 SSLP markers, we genotyped a 68 Mb region on rat chromosome 1 previously implicated in glucose and insulin regulation. We used linkage disequilibrium mapping by mixed model regression with inferred descent to identify a region from 198.85 to 205.9 that contains one or more quantitative trait loci (QTL) for fasting insulin and a measure of insulin resistance, the quantitative insulin sensitivity check index. This region also encompasses loci identified for fasting glucose and Insulin_AUC (area under the curve). A separate <3 Mb QTL was identified for body weight. Using a novel penalized regression method we then estimated effects of alternative haplotype pairings under each locus. These studies highlight the utility of HS rats for fine-mapping genetic loci involved in the underlying causes of T2D.

  2. Accurate expressions for solar cell fill factors including series and shunt resistances

    NASA Astrophysics Data System (ADS)

    Green, Martin A.

    2016-02-01

    Together with open-circuit voltage and short-circuit current, fill factor is a key solar cell parameter. In their classic paper on limiting efficiency, Shockley and Queisser first investigated this factor's analytical properties showing, for ideal cells, it could be expressed implicitly in terms of the maximum power point voltage. Subsequently, fill factors usually have been calculated iteratively from such implicit expressions or from analytical approximations. In the absence of detrimental series and shunt resistances, analytical fill factor expressions have recently been published in terms of the Lambert W function available in most mathematical computing software. Using a recently identified perturbative relationship, exact expressions in terms of this function are derived in technically interesting cases when both series and shunt resistances are present but have limited impact, allowing a better understanding of their effect individually and in combination. Approximate expressions for arbitrary shunt and series resistances are then deduced, which are significantly more accurate than any previously published. A method based on the insights developed is also reported for deducing one-diode fits to experimental data.

  3. EDITORIAL: 15th Workshop on MHD Stability Control: 3D Magnetic Field Effects in MHD Control 15th Workshop on MHD Stability Control: 3D Magnetic Field Effects in MHD Control

    NASA Astrophysics Data System (ADS)

    Buttery, Richard

    2011-08-01

    This annual workshop on MHD Stability Control has been held since 1996 with a focus on understanding and developing control of MHD instabilities for future fusion reactors. The workshop generally covers a wide range of stability topics: from disruptions, to tearing modes, error fields, ELMs, resistive wall modes (RWMs) and ideal MHD. It spans many device types, particularly tokamaks, stellarators and reversed field pinches, to pull out commonalities in the physics and improve understanding. In 2010 the workshop was held on 15-17 November at the University of Wisconsin in Madison and was combined with the annual US-Japan MHD Workshop. The theme was `3D Magnetic Field Effects in MHD Control', with a focus on multidisciplinary sessions exploring issues of plasma response to 3D fields, the manifestation of such fields in the plasma, and how they influence stability. This has been a topic of renewed interest, with utilisation of 3D fields for ELM control now planned in ITER, and a focus on the application of such fields for error field correction, disruption avoidance, and RWM control. Key issues included the physics of the interaction, types of coils and harmonic spectra needed to control instabilities, and subsidiary effects such as braking (or rotating) the plasma. More generally, a wider range of issues were discussed including RWM physics, tearing mode physics, disruption mitigation, ballooning stability, the snowflake divertor concept, and the line tied pinch! A novel innovation to the meeting was a panel discussion session, this year on Neoclassical Toroidal Viscosity, which ran well; more will be tried next year. In this special section of Plasma Physics and Controlled Fusion we present several of the invited and contributed papers from the 2010 workshop, which have been subject to the normal refereeing procedures of the journal. These papers give a sense of the exceptional quality of the presentations at this workshop, all of which may be found at http://fusion.gat.com/conferences/mhd

  4. Broken Ergodicity in MHD Turbulence in a Spherical Domain

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.; wang, Yifan

    2011-01-01

    Broken ergodicity (BE) occurs in Fourier method numerical simulations of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence. Although naive statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that low-wave-number coefficients have non-zero mean values that can be very large compared to the associated standard deviation. In other words, large-scale coherent structure (i.e., broken ergodicity) in homogeneous MHD turbulence can spontaneously grow out of random initial conditions. Eigenanalysis of the modal covariance matrices in the probability density functions of ideal statistical theory leads to a theoretical explanation of observed BE in homogeneous MHD turbulence. Since dissipation is minimal at the largest scales, BE is also relevant for resistive magnetofluids, as evidenced in numerical simulations. Here, we move beyond model magnetofluids confined by periodic boxes to examine BE in rotating magnetofluids in spherical domains using spherical harmonic expansions along with suitable boundary conditions. We present theoretical results for 3-D and 2-D spherical models and also present computational results from dynamical simulations of 2-D MHD turbulence on a rotating spherical surface. MHD turbulence on a 2-D sphere is affected by Coriolus forces, while MHD turbulence on a 2-D plane is not, so that 2-D spherical models are a useful (and simpler) intermediate stage on the path to understanding the much more complex 3-D spherical case.

  5. A Novel IL6 Antibody Sensitizes Multiple Tumor Types to Chemotherapy Including Trastuzumab-Resistant Tumors.

    PubMed

    Zhong, Haihong; Davis, April; Ouzounova, Maria; Carrasco, Rosa A; Chen, Cui; Breen, Shannon; Chang, Yong S; Huang, Jiaqi; Liu, Zheng; Yao, Yihong; Hurt, Elaine; Moisan, Jacques; Fung, Michael; Tice, David A; Clouthier, Shawn G; Xiao, Zhan; Wicha, Max S; Korkaya, Hasan; Hollingsworth, Robert E

    2016-01-15

    Elevated levels of the proinflammatory cytokine IL6 are associated with poor survival outcomes in many cancers. Antibodies targeting IL6 and its receptor have been developed for chronic inflammatory disease, but they have not yet been shown to clearly benefit cancer patients, possibly due to antibody potency or the settings in which they have been tested. In this study, we describe the development of a novel high-affinity anti-IL6 antibody, MEDI5117, which features an extended half-life and potent inhibitory effects on IL6 biologic activity. MEDI5117 inhibited IL6-mediated activation of STAT3, suppressing the growth of several tumor types driven by IL6 autocrine signaling. In the same models, MEDI5117 displayed superior preclinical activity relative to a previously developed anti-IL6 antibody. Consistent with roles for IL6 in promoting tumor angiogenesis, we found that MEDI5117 inhibited the growth of endothelial cells, which can produce IL6 and support tumorigenesis. Notably, in tumor xenograft assays in mice, we documented the ability of MEDI5117 to enhance the antitumor activities of chemotherapy or gefitinib in combination treatment regimens. MEDI5117 also displayed robust activity on its own against trastuzumab-resistant HER2(+) tumor cells by targeting the CD44(+)CD24(-) cancer stem cell population. Collectively, our findings extend the evidence of important pleiotropic roles of IL6 in tumorigenesis and drug resistance, and offer a preclinical proof of concept for the use of IL6 antibodies in combination regimens to heighten therapeutic responses and overcome drug resistance.

  6. Antimicrobial Susceptibility Pattern of Methicillin-Resistance Staphylococcus aureus from Different Tertiary Care Hospitals Including Mymensingh Medical College Hospital.

    PubMed

    Roy, S; Hossain, M A; Paul, S K; Haque, N; Barman, T K; Ahmed, S; Nasreen, S A; Hossain, M S; Ahmed, F; Biswas, P; Nahar, F; Begum, H; Islam, M S

    2016-07-01

    The aim of this study was to detect antimicrobial susceptibilities and the presence of drug resistance genes of MRSA from tertiary care hospitals. This study was carried out in the Department of Microbiology, Mymensingh Medical College during the period from Jan, 2015 to Dec, 2015. Clinical samples, including wound swab, pus, exudates from diabetic ulcer and burn ulcer, aural swab, blood and urine were collected. Standard microbiological procedure & biochemical tests were carried out to detect S. aureus. Oxacillin disk diffusion test was done by Kirby-Bauer disk diffusion method. Total 69 isolates of S. aureus were selected for the study. The isolates were collected from three different tertiary care hospitals, of which 33, 27 and 9 were from Mymensingh Medical College Hospital (MMCH), BIRDEM hospital and Sir Salimullah Medical College Hospital (SSMCH) respectively. Among the 69 isolates, 17(24.6%) and 52(75.3%) were distinguished as MRSA and MSSA respectively by ODDM (Oxacillin disk diffusion method). In contrast, detection of presence and absence of mecA gene by PCR identified 20 (28.9%) and 49 (71.01%) isolates as MRSA and MSSA respectively. All of the S. aureus (MRSA and MSSA) isolates were sensitive to vancomycin and gentamicin. All MRSA isolates (100%) showed resistance to Penicillin and Oxacillin. Among the MRSA isolates about 88.2% were resistance to Ceftazidime, 64.7% were resistance to Erythromycin and Ciprofloxacin, 11.7% were resistance to Tetracycline. Among the MSSA isolates about 94.2% were resistance to Penicillin and 9.6% resistance to Ciprofloxacin. The MSSA were less resistance for non-beta lactam drugs than MRSA. Regarding drug resistance genes, the blaZ genes were present in 47 out of 49(95.8%) MSSA and in 18 out of 18 (100%) MRSA. The erythromycin resistance gene ermB was found in 8.69% isolates, of which highest 20% in MRSA and 4.08% in MSSA. The ermA was not found in any isolates. Among tetracycline resistance genes, tetK were detected in 10

  7. On the global solvability and the non-resistive limit of the one-dimensional compressible heat-conductive MHD equations

    NASA Astrophysics Data System (ADS)

    Zhang, Jianwen; Zhao, Xiaokui

    2017-03-01

    In general, the resistivity is inversely proportional to the electrical conductivity and is usually taken to be zero when the conducting fluid is of extremely high conductivity (e.g., ideal conductors). In this paper, the global well-posedness of strong solution to the one-dimensional compressible, viscous, heat-conductive, non-resistive magnetohydrodynamics equations with large data, and general heat-conductivity is proved. Moreover, the non-resistive limit is justified and the convergence rates in L2-norm are obtained, provided the heat-conductivity satisfies some growth condition.

  8. MHD thrust vectoring of a rocket engine

    NASA Astrophysics Data System (ADS)

    Labaune, Julien; Packan, Denis; Tholin, Fabien; Chemartin, Laurent; Stillace, Thierry; Masson, Frederic

    2016-09-01

    In this work, the possibility to use MagnetoHydroDynamics (MHD) to vectorize the thrust of a solid propellant rocket engine exhaust is investigated. Using a magnetic field for vectoring offers a mass gain and a reusability advantage compared to standard gimbaled, elastomer-joint systems. Analytical and numerical models were used to evaluate the flow deviation with a 1 Tesla magnetic field inside the nozzle. The fluid flow in the resistive MHD approximation is calculated using the KRONOS code from ONERA, coupling the hypersonic CFD platform CEDRE and the electrical code SATURNE from EDF. A critical parameter of these simulations is the electrical conductivity, which was evaluated using a set of equilibrium calculations with 25 species. Two models were used: local thermodynamic equilibrium and frozen flow. In both cases, chlorine captures a large fraction of free electrons, limiting the electrical conductivity to a value inadequate for thrust vectoring applications. However, when using chlorine-free propergols with 1% in mass of alkali, an MHD thrust vectoring of several degrees was obtained.

  9. Conceptual design of the MHD Engineering Test Facility

    NASA Astrophysics Data System (ADS)

    Bents, D. J.; Bercaw, R. W.; Burkhart, J. A.; Mroz, T. S.; Rigo, H. S.; Pearson, C. V.; Warinner, D. K.; Hatch, A. M.; Borden, M.; Giza, D. A.

    The reference conceptual design of the MHD engineering test facility, a prototype 200 MWe coal-fired electric generating plant designed to demonstrate the commerical feasibility of open cycle MHD is summarized. Main elements of the design are identified and explained, and the rationale behind them is reviewed. Major systems and plant facilities are listed and discussed. Construction cost and schedule estimates are included and the engineering issues that should be reexamined are identified.

  10. Conceptual design of the MHD Engineering Test Facility

    NASA Technical Reports Server (NTRS)

    Bents, D. J.; Bercaw, R. W.; Burkhart, J. A.; Mroz, T. S.; Rigo, H. S.; Pearson, C. V.; Warinner, D. K.; Hatch, A. M.; Borden, M.; Giza, D. A.

    1981-01-01

    The reference conceptual design of the MHD engineering test facility, a prototype 200 MWe coal-fired electric generating plant designed to demonstrate the commerical feasibility of open cycle MHD is summarized. Main elements of the design are identified and explained, and the rationale behind them is reviewed. Major systems and plant facilities are listed and discussed. Construction cost and schedule estimates are included and the engineering issues that should be reexamined are identified.

  11. Culture methods impact recovery of antibiotic-resistant Enterococci including Enterococcus cecorum from pre- and postharvest chicken.

    PubMed

    Suyemoto, M M; Barnes, H J; Borst, L B

    2017-03-01

    Pathogenic strains of Enterococcus cecorum (EC) expressing multidrug resistance have emerged. In National Antimicrobial Resistance Monitoring System (NARMS) data, EC is rarely recovered from chickens. Two NARMS methodologies (FDA and USDA) were compared with standard culture (SC) techniques for recovery of EC. NARMS methods failed to detect EC in 58 caecal samples, 20 chicken breast or six whole broiler samples. EC was recovered from 1 of 38 (2·6%) and 2 of 38 (5·2%) preharvest spinal lesions (USDA and FDA method, respectively). In contrast, using the SC method, EC was recovered from 44 of 53 (83%) caecal samples, all 38 (100%) spinal lesions, 14 of 20 (70%) chicken breast samples, and all three spinal lesions identified in whole carcasses. Compared with other Enterococcus spp., EC isolates had a higher prevalence of resistance to macrolides. The NARMS methods significantly affected recovery of enterococcal species other than EC. When the postharvest FDA method was applied to preharvest caecal samples, isolates of Enterococcus faecium were preferentially recovered. All 11 E. faecium isolates were multidrug resistant, including resistance to penicillin, daptomycin and linezolid. These findings confirm that current methodologies may not accurately identify the amount and range of antimicrobial resistance of enterococci from chicken sources.

  12. Susceptibility trends including emergence of linezolid resistance among coagulase-negative staphylococci and meticillin-resistant Staphylococcus aureus from invasive infections.

    PubMed

    Decousser, Jean-Winoc; Desroches, Marine; Bourgeois-Nicolaos, Nadège; Potier, Julien; Jehl, François; Lina, Gérard; Cattoir, Vincent; Vandenesh, François; Doucet-Populaire, Florence

    2015-12-01

    Multiresistance in staphylococci constitutes a major challenge for the antimicrobial chemotherapy of invasive infections such as bacteraemia or bone and joint infections (BJIs). A nationwide prospective study was performed to detect antimicrobial resistance trends among staphylococci causing invasive infections. Between October 2011 and February 2012, 367 meticillin-resistant Staphylococcus aureus (MRSA) and 695 coagulase-negative staphylococci (CoNS) were collected from 37 French hospitals, mainly from bacteraemia (59.9%) and osteoarticular infections (29.0%). Minimum inhibitory concentrations (MICs) were determined by broth microdilution, and specific screening and confirmation tests were performed to detect heterogeneous vancomycin-intermediate S. aureus (hVISA). Staphylococcal isolates exhibiting a linezolid MIC>4 mg/L were further characterised to determinate their clonal relationships and the mechanism of resistance. MRSA exhibited additional resistances, including levofloxacin (82% associated resistance), gentamicin (13.6%), fusidic acid (13.6%) and rifampicin (6.5%), compromising oral step-down therapy in BJIs. Only two hVISA strains (0.5%) were identified. Among the CoNS, mainly Staphylococcus epidermidis (506/695; 72.8%), resistance to first- and second-line agents was more common. Linezolid resistance was identified in 10 CoNS (1.4%). The most frequent linezolid resistance mechanism was the G2576T mutation in 23S rDNA (9/10). For the first time in France, the cfr gene was found in five related sequence type 2 (ST2) S. epidermidis from two different hospitals, in association with ribosomal RNA and L3 ribosomal protein mutations. These national data must be considered when selecting empirical treatment for invasive staphylococcal infections. Moreover, the emergence and spread of linezolid-resistant CoNS carrying the cfr gene is of concern.

  13. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-02-01

    A summary of the work is excerpted here. Final design of an MHD channel for the ITC program POC test has been completed. The channel was designed to be capable of 1.5 MW {sub e} power output and a lifetime of 2000 hours. Emphasis was placed upon durability and reliability. Hence, specific measures were taken to design against channel damage due to electric faults. The life-limiting issues associated with electrochemical corrosion and erosion of gas-side surfaces were addressed by the use of various materials with proven wear characteristics in a coal-fired MHD channel environment. Pitting of prototypical sidewall coupons was observed in the CDIF workhorse testing. The most likely cause of the observed pitting, water leaks resulting from cooling water tube braze failures, has been remedied. New brazing procedures and isolation of the sidebar gas-side material from water contact will prevent sidebar pitting in the prototypical channel. Water-side corrosion tests reported in this quarterly report include the latest results of tungsten-copper elements at controlled pH, heat flux and voltage levels. In the combustion subsystem, efforts continued to focus on understanding and improving the current levels of slag recovery and seed utilization achieved by the combustor. Analytical support was also provided in the areas of slag rejection system operation, precombustor operation, and oil burner design modification. Channel data analysis activities continued in support of prototypical coupon testing at the CDIF. Analyses are presented on channel wall slagging behavior and sidewall voltage distributions.

  14. Laser-powered MHD generators for space application

    NASA Technical Reports Server (NTRS)

    Jalufka, N. W.

    1986-01-01

    Magnetohydrodynamic (MHD) energy conversion systems of the pulsed laser-supported detonation (LSD) wave, plasma MHD, and liquid-metal MHD (LMMHD) types are assessed for their potential as space-based laser-to-electrical power converters. These systems offer several advantages as energy converters relative to the present chemical, nuclear, and solar devices, including high conversion efficiency, simple design, high-temperature operation, high power density, and high reliability. Of these systems, the Brayton cycle liquid-metal MHD system appears to be the most attractive. The LMMHD technology base is well established for terrestrial applications, particularly with regard to the generator, mixer, and other system components. However, further research is required to extend this technology base to space applications and to establish the technology required to couple the laser energy into the system most efficiently. Continued research on each of the three system types is recommended.

  15. MHD Technology Transfer, Integration and Review Committee

    SciTech Connect

    Not Available

    1992-01-01

    This fifth semi-annual status report of the MHD Technology Transfer, Integration, and Review Committee (TTIRC) summarizes activities of the TTIRC during the period April 1990 through September 1990. It includes summaries and minutes of committee meetings, progress summaries of ongoing Proof-of-Concept (POC) contracts, discussions pertaining to technical integration issues in the POC program, and planned activities for the next six months.

  16. The Role of Kinetic Effects, Including Plasma Rotation and Energetic Particles, in Resistive Wall Mode Stability

    NASA Astrophysics Data System (ADS)

    Berkery, John W.

    2009-11-01

    Continuous, disruption-free operation of tokamaks requires stabilization of the resistive wall mode (RWM). Theoretically, the RWM is thought to be stabilized by energy dissipation mechanisms that depend on plasma rotation and other parameters, with kinetic effects being emphasized.footnotetextB. Hu et al., Phys. Plasmas 12 (2005) 057301. Experiments in NSTX show that the RWM can be destabilized in high rotation plasmas while low rotation plasmas can be stable, which calls into question the concept of a simple critical plasma rotation threshold for stability. The present work tests theoretical stabilization mechanisms against experimental discharges with various plasma rotation profiles created by applying non-resonant n=3 braking, and with various fast particle fractions. Kinetic modification of ideal stability is calculated with the MISK code, using experimental equilibrium reconstructions. Analysis of NSTX discharges with unstable RWMs predicts near-marginal mode growth rates. Trapped ions provide the dominant kinetic resonances, while fast particles contribute an important stabilizing effect. Increasing or decreasing rotation in the calculation drives the prediction farther from the marginal point, showing that unlike simpler critical rotation theories, kinetic theory allows a more complex relationship between plasma rotation and RWM stability. Results from JT-60U show that energetic particle modes can trigger RWMsfootnotetextG. Matsunaga et al., IAEA FEC 2008 Paper EX/5-2.. Kinetic theory may explain how fast particle loss can trigger RWMs through the loss of an important stabilization mechanism. These results are applied to ITER advanced scenario equilibria to determine the impact on RWM stability.

  17. Including dietary fiber and resistant starch to increase satiety and reduce aggression in gestating sows

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The swine industry is under a great deal of pressure to return sows to group housing. However, aggression during mixing of pregnant sows impacts sow welfare and productivity. The aim of this study was to increase satiety and reduce aggression by including dietary fiber and fermentable carbohydrate. ...

  18. MHD channel development, part 3

    NASA Astrophysics Data System (ADS)

    1989-12-01

    This is the final report of work performed by Avco Research Laboratory, Inc. for the U.S. Department of Energy, Pittsburgh Energy Technology Center. The overall objectives of this program were: to contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at the 50 MW(sub th) and ultimately at commercial sizes; and to design and fabricate specific hardware items to be tested at a site to be specified by DOE. Section 3.0, MHD Channel Design and Performance, reports experimental and analytical investigations related to MHD channel design and performance.

  19. MHD channel performance for potential early commercial MHD power plants

    NASA Technical Reports Server (NTRS)

    Swallom, D. W.

    1981-01-01

    The commercial viability of full and part load early commercial MHD power plants is examined. The load conditions comprise a mass flow of 472 kg/sec in the channel, Rosebud coal, 34% by volume oxygen in the oxidizer preheated to 922 K, and a one percent by mass seeding with K. The full load condition is discussed in terms of a combined cycle plant with optimized electrical output by the MHD channel. Various electrical load parameters, pressure ratios, and magnetic field profiles are considered for a baseload MHD generator, with a finding that a decelerating flow rate yields slightly higher electrical output than a constant flow rate. Nominal and part load conditions are explored, with a reduced gas mass flow rate and an enriched oxygen content. An enthalpy extraction of 24.6% and an isentropic efficiency of 74.2% is predicted for nominal operation of a 526 MWe MHD generator, with higher efficiencies for part load operation.

  20. MHD turbulent mixing layers

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Benjamin, R.A.; Cho, J.; Leitner, S.N.

    2005-09-28

    Turbulent mixing layers have been proposed to explain observations of line ratios of highly ionized elements in the interstellar medium. We present preliminary results of numerical simulations of turbulent mixing layers in a magnetized medium. We developed a MHD code with radiative cooling. The magnetic field is expected to be a controlling factor by suppressing instabilities that lead to the turbulent mixing. Our results suggest that the difference in turbulent mixing in the unmagnetized case as compared to the case of a weak magnetic field, {beta} = Pgas/Pmag {approx} 10, is insignificant. With a more thorough exploration of parameter space, this work will provide more reliable diagnostics of turbulent mixing layers than those available today.

  1. Production of MHD fluid

    DOEpatents

    Lacey, James J.; Kurtzrock, Roy C.; Bienstock, Daniel

    1976-08-24

    A hot gaseous fluid of low ash content, suitable for use in open-cycle MHD (magnetohydrodynamic) power generation, is produced by means of a three-stage process comprising (1) partial combustion of a fossil fuel to produce a hot gaseous product comprising CO.sub.2 CO, and H.sub.2 O, (2) reformation of the gaseous product from stage (1) by means of a fluidized char bed, whereby CO.sub.2 and H.sub.2 O are converted to CO and H.sub.2, and (3) combustion of CO and H.sub.2 from stage (2) to produce a low ash-content fluid (flue gas) comprising CO.sub.2 and H.sub.2 O and having a temperature of about 4000.degree. to 5000.degree.F.

  2. A Mechanism for the Loading-Unloading Substorm Cycle Missing in MHD Global Magnetospheric Simulation Models

    NASA Technical Reports Server (NTRS)

    Klimas, A. J.; Uritsky, V.; Vassiliadis, D.; Baker, D. N.

    2005-01-01

    Loading and consequent unloading of magnetic flux is an essential element of the substorm cycle in Earth's magnetotail. We are unaware of an available global MHD magnetospheric simulation model that includes a loading- unloading cycle in its behavior. Given the central role that MHD models presently play in the development of our understanding of magnetospheric dynamics, and given the present plans for the central role that these models will play in ongoing space weather prediction programs, it is clear that this failure must be corrected. A 2-dimensional numerical driven current-sheet model has been developed that incorporates an idealized current- driven instability with a resistive MHD system. Under steady loading, the model exhibits a global loading- unloading cycle. The specific mechanism for producing the loading-unloading cycle will be discussed. It will be shown that scale-free avalanching of electromagnetic energy through the model, from loading to unloading, is carried by repetitive bursts of localized reconnection. Each burst leads, somewhat later, to a field configuration that is capable of exciting a reconnection burst again. This process repeats itself in an intermittent manner while the total field energy in the system falls. At the end of an unloading interval, the total field energy is reduced to well below that necessary to initiate the next unloading event and, thus, a loading-unloading cycle results. It will be shown that, in this model, it is the topology of bursty localized reconnection that is responsible for the appearance of the loading-unloading cycle.

  3. Adaptive Numerical Dissipation Control in High Order Schemes for Multi-D Non-Ideal MHD

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, B.

    2005-01-01

    The required type and amount of numerical dissipation/filter to accurately resolve all relevant multiscales of complex MHD unsteady high-speed shock/shear/turbulence/combustion problems are not only physical problem dependent, but also vary from one flow region to another. In addition, proper and efficient control of the divergence of the magnetic field (Div(B)) numerical error for high order shock-capturing methods poses extra requirements for the considered type of CPU intensive computations. The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free from numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multiresolution wavelets (WAV) (for the above types of flow feature). These filters also provide a natural and efficient way for the minimization of Div(B) numerical error.

  4. The role of the electron convection term for the parallel electric field and electron acceleration in MHD simulations

    SciTech Connect

    Matsuda, K.; Terada, N.; Katoh, Y.; Misawa, H.

    2011-08-15

    There has been a great concern about the origin of the parallel electric field in the frame of fluid equations in the auroral acceleration region. This paper proposes a new method to simulate magnetohydrodynamic (MHD) equations that include the electron convection term and shows its efficiency with simulation results in one dimension. We apply a third-order semi-discrete central scheme to investigate the characteristics of the electron convection term including its nonlinearity. At a steady state discontinuity, the sum of the ion and electron convection terms balances with the ion pressure gradient. We find that the electron convection term works like the gradient of the negative pressure and reduces the ion sound speed or amplifies the sound mode when parallel current flows. The electron convection term enables us to describe a situation in which a parallel electric field and parallel electron acceleration coexist, which is impossible for ideal or resistive MHD.

  5. Advances in Simulation of Wave Interaction with Extended MHD Phenomena

    SciTech Connect

    Batchelor, Donald B; Abla, Gheni; D'Azevedo, Ed F; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, Joshua; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Foley, S.; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.

    2009-01-01

    The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: 1) recent improvements to the IPS, 2) application of the IPS for very high resolution simulations of ITER scenarios, 3) studies of resistive and ideal MHD stability in tokamk discharges using IPS facilities, and 4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

  6. Advances in Simulation of Wave Interactions with Extended MHD Phenomena

    SciTech Connect

    Batchelor, Donald B; D'Azevedo, Eduardo; Bateman, Glenn; Bernholdt, David E; Bonoli, P.; Bramley, Randall B; Breslau, Joshua; Elwasif, Wael R; Foley, S.; Jaeger, Erwin Frederick; Jardin, S. C.; Klasky, Scott A; Kruger, Scott E; Ku, Long-Poe; McCune, Douglas; Ramos, J.; Schissel, David P; Schnack, Dalton D

    2009-01-01

    The Integrated Plasma Simulator (IPS) provides a framework within which some of the most advanced, massively-parallel fusion modeling codes can be interoperated to provide a detailed picture of the multi-physics processes involved in fusion experiments. The presentation will cover four topics: (1) recent improvements to the IPS, (2) application of the IPS for very high resolution simulations of ITER scenarios, (3) studies of resistive and ideal MHD stability in tokamak discharges using IPS facilities, and (4) the application of RF power in the electron cyclotron range of frequencies to control slowly growing MHD modes in tokamaks and initial evaluations of optimized location for RF power deposition.

  7. Magnetohydrodynamics (MHD) Engineering Test Facility (ETF) 200 MWe power plant Conceptual Design Engineering Report (CDER)

    NASA Technical Reports Server (NTRS)

    1981-01-01

    The reference conceptual design of the magnetohydrodynamic (MHD) Engineering Test Facility (ETF), a prototype 200 MWe coal-fired electric generating plant designed to demonstrate the commercial feasibility of open cycle MHD, is summarized. Main elements of the design, systems, and plant facilities are illustrated. System design descriptions are included for closed cycle cooling water, industrial gas systems, fuel oil, boiler flue gas, coal management, seed management, slag management, plant industrial waste, fire service water, oxidant supply, MHD power ventilating

  8. Design of closed-cycle MHD generator with nonequilibrium ionization and system

    NASA Technical Reports Server (NTRS)

    Voshall, R. E.; Wright, R. J.; Liebermann, R. W.

    1977-01-01

    A method is developed to include the nonequilibrium ionization process in the MHD generator duct design equations, and these equations are coupled to the thermodynamic conditions of the closed cycle system. This is used to relate MHD generator size, configuration and gas conditions to the overall thermodynamic efficiency of the system. The system studied consists of an MHD loop (Ar + Cs or He + Cs) topping a steam bottoming plant.

  9. The Termination Shock and Beyond: MHD Modeling

    SciTech Connect

    Ratkiewicz, Romana; Grygorczuk, Jolanta; Ben-Jaffel, Lotfi

    2005-08-01

    The 3D MHD models of the solar wind - interstellar plasma interaction including, in a self-consistent way, interactions of various populations of plasma and neutral particles should be ready to confront their results with the forthcoming data that will be obtained from space missions. In the near future, predictions made by sophisticated theoretical models should help refine the goals and optimize the capabilities of the instruments that will explore the far heliosphere and the LISM. In this paper we are giving a short survey of the MHD models and point out the problems, which need to be solved in the near future. As the example we show our recent numerical results with the simple model of the current sheet.

  10. Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions.

    PubMed

    Butler, Jason E; Shaqfeh, Eric S G

    2005-01-01

    Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the "freely draining" case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.

  11. Brownian dynamics simulations of a flexible polymer chain which includes continuous resistance and multibody hydrodynamic interactions

    NASA Astrophysics Data System (ADS)

    Butler, Jason E.; Shaqfeh, Eric S. G.

    2005-01-01

    Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the "freely draining" case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.

  12. MHD channel development, part 4

    NASA Astrophysics Data System (ADS)

    1989-12-01

    This is the final report of work performed by Avco Research Laboratory, Inc. for the U.S. Department of Energy, Pittsburgh Energy Technology Center. The overall objectives of this program were: to contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at the 50 MW(sub th) and ultimately at commercial sizes; and to design and fabricate specific hardware items to be tested at a site to be specified by DOE. The program consisted of a series of related tasks, which are described in subsequent sections of this report. Section 4.0, MHD Channel Construction and Lifetime, reports experimental investigations related to MHD channel reliability and lifetime, where the principal aim is to improve the constructability, maintainability, and reliability of coal-fired, long-duration MHD channels.

  13. Latent introduction to the Netherlands of multiple antibiotic resistance including NDM-1 after hospitalisation in Egypt, August 2013.

    PubMed

    Bathoorn, E; Friedrich, A W; Zhou, K; Arends, J P; Borst, D M; Grundmann, H; Rossen, J W

    2013-10-17

    We describe the introduction of various multi-drug resistant bacterial strains, including an NDM-1-producing Klebsiella pneumoniae, through a traveller returning from Egypt, where they had been admitted to a private hospital. All family members of the patient were colonised with one or more extended-spectrum beta-lactamase producing strains. These findings emphasise the importance of adherence to isolation precautions for returning patients and suggest the need for inclusion of Enterobacteriaceae in admission screening.

  14. Propagation and Dissipation of MHD Waves in Coronal Holes

    NASA Astrophysics Data System (ADS)

    Dwivedi, B. N.

    2006-11-01

    bholadwivedi@gmail.com In view of the landmark result on the solar wind outflow, starting between 5 Mm and 20 Mm above the photosphere in magnetic funnels, we investigate the propagation and dissipation of MHD waves in coronal holes. We underline the importance of Alfvén wave dissipation in the magnetic funnels through the viscous and resistive plasma. Our results show that Alfvén waves are one of the primary energy sources in the innermost part of coronal holes where the solar wind outflow starts. We also consider compressive viscosity and thermal conductivity to study the propagation and dissipation of long period slow longitudinal MHD waves in polar coronal holes. We discuss their likely role in the line profile narrowing, and in the energy budget for coronal holes and the solar wind. We compare the contribution of longitudinal MHD waves with high frequency Alfvén waves.

  15. Perturbed Stability Analysis of External Ideal MHD Modes

    NASA Astrophysics Data System (ADS)

    Comer, K. J.; Callen, J. D.; Hegna, C. C.; Garstka, G. D.; Turnbull, A. D.; Garofalo, A. M.; Cowley, S. C.

    2002-11-01

    Traditionally, numerical parameter scans are performed to study the effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities. Previously, we introduced a new perturbative technique to more efficiently explore these dependencies: changes in delta-W due to small equilibrium variations are found using a perturbation of the energy principle rather than with an eigenvalue-solver instability code. With this approach, the stability properties of similar equilibria can be efficiently explored without generating complete numerical results for every set of parameters (which is time-intensive for accurate representations of several configurations). Here, we apply this approach to toroidal geometry using GATO (an ideal MHD stability code) and experimental equilibria. In particular, we explore ideal MHD stability of external kink modes in the spherical tokamak Pegasus and resistive wall modes in DIII-D.

  16. Performance evaluations of MHD generator tests at CDIF

    NASA Astrophysics Data System (ADS)

    Daniel, V. W.; Lineberry, J. T.; Wu, Y. C. L.

    1992-01-01

    Experimental data from CDIF coal-fired MHD generator test 90-DIAG-3 are analyzed. The results of two independent studies are presented and compared. Both studies impose experimental data upon modeling to derive information on plasma properties and electrical loss mechanisms. The first technique applies routine electrical data to special solutions of the MHD electrical equations to determine gross electrophysical properties and nonuniformity parameters of the generator medium (plasma plus slag) over one pitch control volumes along the length of the MHD channel. The second technique pits a predictive 1D MHD generator model against input experimental Hall voltage data. The generator model solves for the MHD plasmadynamic and electrical processes required to fit the experimental voltage distribution to determine plasma properties with wall and electrical losses. Among the parameters that are estimated by these methods are conductivity, Hall parameter, interelectrode resistances, and the plasma nonuniformity factors (e.g., G). The magnitude of leakage current (slag or otherwise) can also inferred from these analyses.

  17. Dynamo action in dissipative, forced, rotating MHD turbulence

    NASA Astrophysics Data System (ADS)

    Shebalin, John V.

    2016-06-01

    Magnetohydrodynamic (MHD) turbulence is an inherent feature of large-scale, energetic astrophysical and geophysical magnetofluids. In general, these are rotating and are energized through buoyancy and shear, while viscosity and resistivity provide a means of dissipation of kinetic and magnetic energy. Studies of unforced, rotating, ideal (i.e., non-dissipative) MHD turbulence have produced interesting results, but it is important to determine how these results are affected by dissipation and forcing. Here, we extend our previous work and examine dissipative, forced, and rotating MHD turbulence. Incompressibility is assumed, and finite Fourier series represent turbulent velocity and magnetic field on a 643 grid. Forcing occurs at an intermediate wave number by a method that keeps total energy relatively constant and allows for injection of kinetic and magnetic helicity. We find that 3-D energy spectra are asymmetric when forcing is present. We also find that dynamo action occurs when forcing has either kinetic or magnetic helicity, with magnetic helicity injection being more important. In forced, dissipative MHD turbulence, the dynamo manifests itself as a large-scale coherent structure that is similar to that seen in the ideal case. These results imply that MHD turbulence, per se, may play a fundamental role in the creation and maintenance of large-scale (i.e., dipolar) stellar and planetary magnetic fields.

  18. C-Mod MHD stability analysis with LHCD

    NASA Astrophysics Data System (ADS)

    Ebrahimi, Fatima; Bhattacharjee, A.; Delgado, L.; Scott, S.; Wilson, J. R.; Wallace, G. M.; Shiraiwa, S.; Mumgaard, R. T.

    2016-10-01

    In lower hybrid current drive (LHCD) experiments on the Alcator C-Mod, sawtooth activity could be suppressed as the safety factor q on axis is raised above unity. However, in some of these experiments, after applying LHCD, the onset of MHD mode activity caused the current drive efficiency to significantly drop. Here, we study the stability of these experiments by performing MHD simulations using the NIMROD code starting with experimental EFIT equilibria. First, consistent with the LHCD experiment with no signature of MHD activity, MHD mode activity was also absent in the simulations. Second, for experiments with MHD mode activity, we find that a core n=1 reconnecting mode with dominate poloidal modes of m=2,3 is unstable. This mode is a resistive current-driven mode as its growth rate scales with a negative power of the Lundquist number in the simulations. In addition, with further enhanced reversed-shear q profile in the simulations, a core double tearing mode is found to be unstable. This work is supported by U.S. DOE cooperative agreement DE-FC02-99ER54512 using the Alcator C-Mod tokamak, a DOE Office of Science user facility.

  19. An Antimicrobial Metabolite from Bacillus sp.: Significant Activity Against Pathogenic Bacteria Including Multidrug-Resistant Clinical Strains

    PubMed Central

    Chalasani, Ajay G.; Dhanarajan, Gunaseelan; Nema, Sushma; Sen, Ramkrishna; Roy, Utpal

    2015-01-01

    In this study, the cell free modified tryptone soya broth (pH 7.4 ± 0.2) of Bacillus subtilis URID 12.1 showed significant antimicrobial activity against multidrug-resistant strains of Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes and Enterococcus faecalis. The partially purified antimicrobial molecule was found to be resistant to extremes of pH and temperatures and also to higher concentrations of trypsin and proteinase K. The antimicrobial molecule was purified by a three-step method that included reversed-phase high performance liquid chromatography (RP-HPLC). The minimum inhibitory concentration (MIC) values were determined for 14 species of bacteria using a microbroth dilution technique. The HPLC-purified fraction showed the MICs ranging from 0.5 to 16 μg/ml for methicillin and vancomycin-resistant Staphylococcus aureus (MVRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE) strains. The molecular mass of the antimicrobial compound was determined to be 842.37 Da. The same antimicrobial fraction showed negligible haemolytic activity against human red blood cells even at a concentration as high as 100 μg/ml. Because of its significant antimicrobial activity at low MIC values coupled with its non-haemolytic property, it may prove to be a novel antimicrobial lead molecule. PMID:26696963

  20. Thermodynamic MHD Modeling of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Linker, Jon A.; Lionello, R.; Mikic, Z.; Riley, P.; Titov, V.

    2007-05-01

    Coronal mass ejections (CMEs) disrupt the large-scale coronal magnetic field and propel plasma and magnetic flux outward into interplanetary space. The most energetic CMEs typically originate from active regions on the Sun. Accurately modeling active regions while also capturing the entire corona requires MHD models that include energy transport (radiative losses,anisotropic thermal conduction, and coronal heating) in the transition region and solar corona. We refer to this as the thermodynamic MHD model. The more accurate representation of energy flow in the thermodynamic MHD model allows us to to compute simulated EUV and X-ray emission as would be observed from spacecraft such as SOHO, STEREO, and Hinode. With this approach, theorists no longer get to argue what emission they think their favorite model's magnetic field evolution implies; we can actually go compute the emission and compare with observations. As an example, we show a simulation of the May 12, 1997 CME, and compare the simulated emission with observations from the actual event of dimming regions, postflare loops, and reformation of loops near the northern polar coronal hole. Work supported by NASA, NSF and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center).

  1. MHD-EMP protection guidelines

    SciTech Connect

    Barnes, P.R.; Vance, E.F.

    1992-01-01

    A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earth's magnetic field and result in a strong magnetohyrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. The geomagnetic disturbance interacts with the soil to induced current and horizontal electric gradients in the earth. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after the exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in it's global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

  2. The Biermann catastrophe of numerical MHD

    NASA Astrophysics Data System (ADS)

    Graziani, C.; Tzeferacos, P.; Lee, D.; Lamb, D. Q.; Weide, K.; Fatenejad, M.; Miller, J.

    2016-05-01

    The Biermann Battery effect is frequently invoked in cosmic magnetogenesis and studied in High-Energy Density laboratory physics experiments. Unfortunately, direct implementation of the Biermann effect in MHD codes is known to produce unphysical magnetic fields at shocks whose value does not converge with resolution. We show that this convergence breakdown is due to naive discretization, which fails to account for the fact that discretized irrotational vector fields have spurious solenoidal components that grow without bound near a discontinuity. We show that careful consideration of the kinetics of ion viscous shocks leads to a formulation of the Biermann effect that gives rise to a convergent algorithm. We note a novel physical effect a resistive magnetic precursor in which Biermann-generated field in the shock “leaks” resistively upstream. The effect appears to be potentially observable in experiments at laser facilities.

  3. Intensive lifestyle intervention including high-intensity interval training program improves insulin resistance and fasting plasma glucose in obese patients☆

    PubMed Central

    Marquis-Gravel, Guillaume; Hayami, Douglas; Juneau, Martin; Nigam, Anil; Guilbeault, Valérie; Latour, Élise; Gayda, Mathieu

    2015-01-01

    Objectives To analyze the effects of a long-term intensive lifestyle intervention including high-intensity interval training (HIIT) and Mediterranean diet (MedD) counseling on glycemic control parameters, insulin resistance and β-cell function in obese subjects. Methods The glycemic control parameters (fasting plasma glucose, glycated hemoglobin), insulin resistance, and β-cell function of 72 obese subjects (54 women; mean age = 53 ± 9 years) were assessed at baseline and upon completion of a 9-month intensive lifestyle intervention program conducted at the cardiovascular prevention and rehabilitation center of the Montreal Heart Institute, from 2009 to 2012. The program included 2–3 weekly supervised exercise training sessions (HIIT and resistance exercise), combined to MedD counseling. Results Fasting plasma glucose (FPG) (mmol/L) (before: 5.5 ± 0.9; after: 5.2 ± 0.6; P < 0.0001), fasting insulin (pmol/L) (before: 98 ± 57; after: 82 ± 43; P = 0.003), and insulin resistance, as assessed by the HOMA-IR score (before: 3.6 ± 2.5; after: 2.8 ± 1.6; P = 0.0008) significantly improved, but not HbA1c (%) (before: 5.72 ± 0.55; after: 5.69 ± 0.39; P = 0.448), nor β-cell function (HOMA-β, %) (before: 149 ± 78; after: 144 ± 75; P = 0.58). Conclusion Following a 9-month intensive lifestyle intervention combining HIIT and MedD counseling, obese subjects experienced significant improvements of FPG and insulin resistance. This is the first study to expose the effects of a long-term program combining HIIT and MedD on glycemic control parameters among obese subjects. PMID:26844086

  4. Coronal extension of the MURaM radiative MHD code: From quiet sun to flare simulations

    NASA Astrophysics Data System (ADS)

    Rempel, Matthias D.; Cheung, Mark

    2016-05-01

    We present a new version of the MURaM radiative MHD code, which includes a treatment of the solar corona in terms of MHD, optically thin radiative loss and field-aligned heat conduction. In order to relax the severe time-step constraints imposed by large Alfven velocities and heat conduction we use a combination of semi-relativistic MHD with reduced speed of light ("Boris correction") and a hyperbolic formulation of heat conduction. We apply the numerical setup to 4 different setups including a mixed polarity quiet sun, an open flux region, an arcade solution and an active region setup and find all cases an amount of coronal heating sufficient to maintain a corona with temperatures from 1 MK (quiet sun) to 2 MK (active region, arcade). In all our setups the Poynting flux is self-consistently created by photospheric and sub-photospheric magneto-convection in the lower part of our simulation domain. Varying the maximum allowed Alfven velocity ("reduced speed of light") leads to only minor changes in the coronal structure as long as the limited Alfven velocity remains larger than the speed of sound and about 1.5-3 times larger than the peak advection velocity. We also found that varying details of the numerical diffusivities that govern the resistive and viscous energy dissipation do not strongly affect the overall coronal heating, but the ratio of resistive and viscous energy dependence is strongly dependent on the effective numerical magnetic Prandtl number. We use our active region setup in order to simulate a flare triggered by the emergence of a twisted flux rope into a pre-existing bipolar active region. Our simulation yields a series of flares, with the strongest one reaching GOES M1 class. The simulation reproduces many observed properties of eruptions such as flare ribbons, post flare loops and a sunquake.

  5. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-03-01

    The Magnetohydrodynamics (MHD) Integrated Topping Cycle (ITC) Project represents the culmination of the proof-of-concept (POC) development stage in the US Department of Energy (DOE) program to advance MHD technology to early commercial development stage utility power applications. The project is a joint effort, combining the skills of three topping cycle component developers: TRW, Avco/TDS, and Westinghouse. TRW, the prime contractor and system integrator, is responsible for the 50 thermal megawatt (50 MW{sub t}) slagging coal combustion subsystem. Avco/TDS is responsible for the MHD channel subsystem (nozzle, channel, diffuser, and power conditioning circuits), and Westinghouse is responsible for the current consolidation subsystem. The ITC Project will advance the state-of-the-art in MHD power systems with the design, construction, and integrated testing of 50 MW{sub t} power train components which are prototypical of the equipment that will be used in an early commercial scale MHD utility retrofit. Long duration testing of the integrated power train at the Component Development and Integration Facility (CDIF) in Butte, Montana will be performed, so that by the early 1990's, an engineering data base on the reliability, availability, maintainability and performance of the system will be available to allow scaleup of the prototypical designs to the next development level. This Sixteenth Quarterly Technical Progress Report covers the period May 1, 1991 to July 31, 1991.

  6. Natural product derivatives with bactericidal activity against Gram-positive pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis.

    PubMed

    Phillips, Joshua B; Smith, Adrienne E; Kusche, Brian R; Bessette, Bradley A; Swain, P Whitney; Bergmeier, Stephen C; McMills, Mark C; Wright, Dennis L; Priestley, Nigel D

    2010-10-01

    We have shown that the intentional engineering of a natural product biosynthesis pathway is a useful way to generate stereochemically complex scaffolds for use in the generation of combinatorial libraries that capture the structural features of both natural products and synthetic compounds. Analysis of a prototype library based upon nonactic acid lead to the discovery of triazole-containing nonactic acid analogs, a new structural class of antibiotic that exhibits bactericidal activity against drug resistant, Gram-positive pathogens including Staphylococcus aureus and Enterococcus faecalis.

  7. Extended MHD Effects in High Energy Density Experiments

    NASA Astrophysics Data System (ADS)

    Seyler, Charles

    2016-10-01

    The MHD model is the workhorse for computational modeling of HEDP experiments. Plasma models are inheritably limited in scope, but MHD is expected to be a very good model for studying plasmas at the high densities attained in HEDP experiments. There are, however, important ways in which MHD fails to adequately describe the results, most notably due to the omission of the Hall term in the Ohm's law (a form of extended MHD or XMHD). This talk will discuss these failings by directly comparing simulations of MHD and XMHD for particularly relevant cases. The methodology is to simulate HEDP experiments using a Hall-MHD (HMHD) code based on a highly accurate and robust Discontinuous Galerkin method, and by comparison of HMHD to MHD draw conclusions about the impact of the Hall term. We focus on simulating two experimental pulsed power machines under various scenarios. We examine the MagLIF experiment on the Z-machine at Sandia National Laboratories and liner experiments on the COBRA machine at Cornell. For the MagLIF experiment we find that power flow in the feed leads to low density plasma ablation into the region surrounding the liner. The inflow of this plasma compresses axial magnetic flux onto the liner. In MHD this axial flux tends to resistively decay, whereas in HMHD a force-free current layer sustains the axial flux on the liner leading to a larger ratio of axial to azimuthal flux. During the liner compression the magneto-Rayleigh-Taylor instability leads to helical perturbations due to minimization of field line bending. Simulations of a cylindrical liner using the COBRA machine parameters can under certain conditions exhibit amplification of an axial field due to a force-free low-density current layer separated by some distance from the liner. This results in a configuration in which there is predominately axial field on the liner inside the current layer and azimuthal field outside the layer. We are currently attempting to experimentally verify the simulation

  8. Outline of fast analyzer for MHD equilibrium FAME

    NASA Astrophysics Data System (ADS)

    Sakata, Shinya; Haginoya, Hirofumi; Tsuruoka, Takuya; Aoyagi, Tetsuo; Saito, Naoyuki; Harada, Hiroo; Tani, Keiji; Watanabe, Hideto

    1994-02-01

    The FAME (Fast Analyzer for Magnetohydrodynamic (MHD) Equilibrium) system has been developed in order to provide more than 100 MHD equilibria in time series which are enough for the non-stationary analysis of the experimental data of JT-60 within about 20 minutes shot interval. The FAME is an MIMD type small scale parallel computer with 20 microprocessors which are connected by a multi-stage switching system. The maximum theoretical speed is 250 MFLOPS. For the software system of FAME, MHD equilibrium analysis code SELENE and its input data production code FBI are tuned up taking the parallel processing into consideration. Consequently, the computational performance of the FAME system becomes more than 7 times faster than the existing general purpose computer FACOM M780-10s. This report summarizes the outline of the FAME system including hardware, soft-ware and peripheral equipments.

  9. Common Hamiltonian and topological properties of extended MHD models

    NASA Astrophysics Data System (ADS)

    Miloshevich, George; Lingam, Manasvi; Morrison, Philip

    2016-10-01

    Extended MHD, a 1-fluid model endowed with 2-fluid effects (electron inertia and Hall drift) possesses a Hamiltonian structure. This formulation is described, as it unifies different classes of extended MHD models (including those that have mutually exclusive effects). The unification is further highlighted by showing that these models possess common topological invariants that are the generalizations of the fluid/magnetic helicity. They can be expressed naturally in a knot-theoretic framework via the Jones polynomial by exploiting techniques from Chern-Simons theory. It is also shown that extended MHD exhibits other commonalities such as: generalized Kelvin circulation theorems, and the existence of two Lie-dragged 2-forms closely connected with generalizations of the fluid vorticity. NSF Grant No. AGS-133894, DOE Grants No. DE-AC02-09CH-11466 and DE-FG02-04ER-54742.

  10. MHD-EMP protection guidelines

    SciTech Connect

    Barnes, P.R.; Vance, E.F.

    1992-03-01

    A nuclear detonation at altitudes several hundred kilometers above the earth will severely distort the earth`s magnetic field and result in a strong magnetohyrodynamic electromagnetic pulse (MHD-EMP). The geomagnetic disturbance interacts with the soil to induce current and horizontal electric gradients. The geomagnetic disturbance interacts with the soil to induced current and horizontal electric gradients in the earth. MHD-EMP, also called E3 since it is the third component of the high-altitude EMP (HEMP), lasts over 100 s after the exoatmospheric burst. MHD-EMP is similar to solar geomagnetic storms in it`s global and low frequency (less than 1 Hz) nature except that E3 can be much more intense with a far shorter duration. When the MHD-EMP gradients are integrated over great distances by power lines, communication cables, or other long conductors, the induced voltages are significant. (The horizontal gradients in the soil are too small to induce major responses by local interactions with facilities.) The long pulse waveform for MHD-EMP-induced currents on long lines has a peak current of 200 A and a time-to-half-peak of 100 s. If this current flows through transformer windings, it can saturate the magnetic circuit and cause 60 Hz harmonic production. To mitigate the effects of MHD-EMP on a facility, long conductors must be isolated from the building and the commercial power harmonics and voltage swings must be addressed. The transfer switch would be expected to respond to the voltage fluctuations as long as the harmonics have not interfered with the switch control circuitry. The major sources of MHD-EMP induced currents are the commercial power lines and neutral; neutral current indirect coupling to the facility power or ground system via the metal fence, powered gate, parking lights, etc; metal water pipes; phone lines; and other long conductors that enter or come near the facility. The major source of harmonics is the commercial power system.

  11. MHD Simulations of the Plasma Flow in the Magnetic Nozzle

    NASA Technical Reports Server (NTRS)

    Smith, T. E. R.; Keidar, M.; Sankaran, K.; olzin, K. A.

    2013-01-01

    The magnetohydrodynamic (MHD) flow of plasma through a magnetic nozzle is simulated by solving the governing equations for the plasma flow in the presence of an static magnetic field representing the applied nozzle. This work will numerically investigate the flow and behavior of the plasma as the inlet plasma conditions and magnetic nozzle field strength are varied. The MHD simulations are useful for addressing issues such as plasma detachment and to can be used to gain insight into the physical processes present in plasma flows found in thrusters that use magnetic nozzles. In the model, the MHD equations for a plasma, with separate temperatures calculated for the electrons and ions, are integrated over a finite cell volume with flux through each face computed for each of the conserved variables (mass, momentum, magnetic flux, energy) [1]. Stokes theorem is used to convert the area integrals over the faces of each cell into line integrals around the boundaries of each face. The state of the plasma is described using models of the ionization level, ratio of specific heats, thermal conductivity, and plasma resistivity. Anisotropies in current conduction due to Hall effect are included, and the system is closed using a real-gas equation of state to describe the relationship between the plasma density, temperature, and pressure.A separate magnetostatic solver is used to calculate the applied magnetic field, which is assumed constant for these calculations. The total magnetic field is obtained through superposition of the solution for the applied magnetic field and the self-consistently computed induced magnetic fields that arise as the flowing plasma reacts to the presence of the applied field. A solution for the applied magnetic field is represented in Fig. 1 (from Ref. [2]), exhibiting the classic converging-diverging field pattern. Previous research was able to demonstrate effects such as back-emf at a super-Alfvenic flow, which significantly alters the shape of the

  12. Global MHD Simulations of Space Plasma Environments: Heliosphere, Comets, Magnetospheres of Plants and Satellites

    NASA Technical Reports Server (NTRS)

    Kabin, K.; Hansen, K. C.; Gombosi, T. I.; Combi, M. R.; Linde, T. J.; DeZeeuw, D. L.; Groth, C. P. T.; Powell, K. G.; Nagy, A. F.

    2000-01-01

    Magnetohydrodynamics (MHD) provides an approximate description of a great variety of processes in space physics. Accurate numerical solutions of the MHD equations are still a challenge, but in the past decade a number of robust methods have appeared. Once these techniques made the direct solution of MHD equations feasible, a number of global three-dimensional models were designed and applied to many space physics objects. The range of these objects is truly astonishing, including active galactic nuclei, the heliosphere, the solar corona, and the solar wind interaction with planets, satellites, and comets. Outside the realm of space physics, MHD theory has been applied to such diverse problems as laboratory plasmas and electromagnetic casting of liquid metals. In this paper we present a broad spectrum of models of different phenomena in space science developed in the recent years at the University of Michigan. Although the physical systems addressed by these models are different, they all use the MHD equations as a unifying basis.

  13. Antimicrobial susceptibility and antibiotic resistance gene transfer analysis of foodborne, clinical, and environmental Listeria spp. isolates including Listeria monocytogenes.

    PubMed

    Bertsch, David; Muelli, Mirjam; Weller, Monika; Uruty, Anaïs; Lacroix, Christophe; Meile, Leo

    2014-02-01

    The aims of this study were to assess antibiotic resistance pheno- and genotypes in foodborne, clinical, and environmental Listeria isolates, as well as to elucidate the horizontal gene transfer potential of detected resistance genes. A small fraction of in total 524 Listeria spp. isolates (3.1%) displayed acquired antibiotic resistance mainly to tetracycline (n = 11), but also to clindamycin (n = 4) and trimethoprim (n = 3), which was genotypically confirmed. In two cases, a tetracycline resistance phenotype was observed together with a trimethoprim resistance phenotype, namely in a clinical L. monocytogenes strain and in a foodborne L. innocua isolate. Depending on the applied guidelines, a differing number of isolates (n = 2 or n = 20) showed values for ampicillin that are on the edge between intermediate susceptibility and resistance. Transferability of the antibiotic resistance genes from the Listeria donors, elucidated in vitro by filter matings, was demonstrated for genes located on transposons of the Tn916 family and for an unknown clindamycin resistance determinant. Transfer rates of up to 10(-5) transconjugants per donor were obtained with a L. monocytogenes recipient and up to 10(-7) with an Enterococcus faecalis recipient, respectively. Although the prevalence of acquired antibiotic resistance in Listeria isolates from this study was rather low, the transferability of these resistances enables further spread in the future. This endorses the importance of surveillance of L. monocytogenes and other Listeria spp. in terms of antibiotic susceptibility.

  14. Region-specific diet-induced and leptin-induced cellular leptin resistance includes the ventral tegmental area in rats.

    PubMed

    Matheny, M; Shapiro, A; Tümer, N; Scarpace, P J

    2011-01-01

    Diet-induced obesity (DIO) results in region-specific cellular leptin resistance in the arcuate nucleus (ARC) of the hypothalamus in one strain of mice and in several medial basal hypothalamic regions in another. We hypothesized that the ventral tegmental area (VTA) is also likely susceptible to diet-induced and leptin-induced leptin resistance in parallel to that in hypothalamic areas. We examined two forms of leptin resistance in F344xBN rats, that induced by 6-months of high fat (HF) feeding and that induced by 15-months of central leptin overexpression by use of recombinant adeno-associated viral (rAAV)-mediated gene delivery of rat leptin. Cellular leptin resistance was assessed by leptin-stimulated phosphorylation of signal transducers and activators of transcription 3 (STAT3) in medial basal hypothalamic areas and the VTA. The regional pattern and degree of leptin resistance with HF was distinctly different than that with leptin overexpression. Chronic HF feeding induced a cellular leptin resistance that was identified in the ARC and VTA, but absent in the lateral hypothalamus (LH), ventromedial hypothalamus (VMH), and dorsomedial hypothalamus (DMH). In contrast, chronic central leptin overexpression induced cellular leptin resistance in all areas examined. The identification of leptin resistance in the VTA, in addition to the leptin resistance in the hypothalamus, provides one potential mechanism, underlying the increased susceptibility of leptin resistant rats to HF-induced obesity.

  15. Adaptive Numerical Dissipative Control in High Order Schemes for Multi-D Non-Ideal MHD

    NASA Technical Reports Server (NTRS)

    Yee, H. C.; Sjoegreen, B.

    2004-01-01

    The goal is to extend our adaptive numerical dissipation control in high order filter schemes and our new divergence-free methods for ideal MHD to non-ideal MHD that include viscosity and resistivity. The key idea consists of automatic detection of different flow features as distinct sensors to signal the appropriate type and amount of numerical dissipation/filter where needed and leave the rest of the region free of numerical dissipation contamination. These scheme-independent detectors are capable of distinguishing shocks/shears, flame sheets, turbulent fluctuations and spurious high-frequency oscillations. The detection algorithm is based on an artificial compression method (ACM) (for shocks/shears), and redundant multi-resolution wavelets (WAV) (for the above types of flow feature). These filter approaches also provide a natural and efficient way for the minimization of Div(B) numerical error. The filter scheme consists of spatially sixth order or higher non-dissipative spatial difference operators as the base scheme for the inviscid flux derivatives. If necessary, a small amount of high order linear dissipation is used to remove spurious high frequency oscillations. For example, an eighth-order centered linear dissipation (AD8) might be included in conjunction with a spatially sixth-order base scheme. The inviscid difference operator is applied twice for the viscous flux derivatives. After the completion of a full time step of the base scheme step, the solution is adaptively filtered by the product of a 'flow detector' and the 'nonlinear dissipative portion' of a high-resolution shock-capturing scheme. In addition, the scheme independent wavelet flow detector can be used in conjunction with spatially compact, spectral or spectral element type of base schemes. The ACM and wavelet filter schemes using the dissipative portion of a second-order shock-capturing scheme with sixth-order spatial central base scheme for both the inviscid and viscous MHD flux

  16. MHD control in burning plasmas MHD control in burning plasmas

    NASA Astrophysics Data System (ADS)

    Donné, Tony; Liang, Yunfeng

    2012-07-01

    Fusion physics focuses on the complex behaviour of hot plasmas confined by magnetic fields with the ultimate aim to develop a fusion power plant. In the future generation of tokamaks like ITER, the power generated by the fusion reactions substantially exceeds the external input power (Pfusion}/Pin >= 10). When this occurs one speaks of a burning plasma. Twenty per cent of the generated fusion power in a burning plasma is carried by the charged alpha particles, which transfer their energy to the ambient plasma in collisions, a process called thermalization. A new phenomenon in burning plasmas is that the alpha particles, which form a minority but carry a large fraction of the plasma kinetic energy, can collectively drive certain types of magneto-hydrodynamic (MHD) modes, while they can suppress other MHD modes. Both types of MHD modes can have desirable effects on the plasma, as well as be detrimental to the plasma. For example, the so-called sawtooth instability, on the one hand, is largely responsible for the transport of the thermalized alpha particles out of the core, but, on the other hand, may result in the loss of the energetic alphas before they have fully thermalized. A further undesirable effect of the sawtooth instability is that it may trigger other MHD modes such as neoclassical tearing modes (NTMs). These NTMs, in turn, are detrimental to the plasma confinement and in some cases may even lead to disruptive termination of the plasma. At the edge of the plasma, finally, so-called edge localized modes or ELMs occur, which result in extremely high transient heat and particle loads on the plasma-facing components of a reactor. In order to balance the desired and detrimental effects of these modes, active feedback control is required. An additional complication occurs in a burning plasma as the external heating power, which is nowadays generally used for plasma control, is small compared to the heating power of the alpha particles. The scientific challenge

  17. GRADSPMHD: A parallel MHD code based on the SPH formalism

    NASA Astrophysics Data System (ADS)

    Vanaverbeke, S.; Keppens, R.; Poedts, S.

    2014-03-01

    We present GRADSPMHD, a completely Lagrangian parallel magnetohydrodynamics code based on the SPH formalism. The implementation of the equations of SPMHD in the “GRAD-h” formalism assembles known results, including the derivation of the discretized MHD equations from a variational principle, the inclusion of time-dependent artificial viscosity, resistivity and conductivity terms, as well as the inclusion of a mixed hyperbolic/parabolic correction scheme for satisfying the ∇ṡB→ constraint on the magnetic field. The code uses a tree-based formalism for neighbor finding and can optionally use the tree code for computing the self-gravity of the plasma. The structure of the code closely follows the framework of our parallel GRADSPH FORTRAN 90 code which we added previously to the CPC program library. We demonstrate the capabilities of GRADSPMHD by running 1, 2, and 3 dimensional standard benchmark tests and we find good agreement with previous work done by other researchers. The code is also applied to the problem of simulating the magnetorotational instability in 2.5D shearing box tests as well as in global simulations of magnetized accretion disks. We find good agreement with available results on this subject in the literature. Finally, we discuss the performance of the code on a parallel supercomputer with distributed memory architecture. Catalogue identifier: AERP_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERP_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 620503 No. of bytes in distributed program, including test data, etc.: 19837671 Distribution format: tar.gz Programming language: FORTRAN 90/MPI. Computer: HPC cluster. Operating system: Unix. Has the code been vectorized or parallelized?: Yes, parallelized using MPI. RAM: ˜30 MB for a

  18. Magnetic levitation and MHD propulsion

    NASA Astrophysics Data System (ADS)

    Tixador, P.

    1994-04-01

    Magnetic levitation and MHD propulsion are now attracting attention in several countries. Different superconducting MagLev and MHD systems will be described concentrating on, above all, the electromagnetic aspect. Some programmes occurring throughout the world will be described. Magnetic levitated trains could be the new high speed transportation system for the 21st century. Intensive studies involving MagLev trains using superconductivity have been carried out in Japan since 1970. The construction of a 43 km long track is to be the next step. In 1991 a six year programme was launched in the United States to evaluate the performances of MagLev systems for transportation. The MHD (MagnetoHydroDynamic) offers some interesting advantages (efficiency, stealth characteristics, ...) for naval propulsion and increasing attention is being paid towards it nowadays. Japan is also up at the top with the tests of Yamato I, a 260 ton MHD propulsed ship. Depuis quelques années nous assistons à un redémarrage de programmes concernant la lévitation et la propulsion supraconductrices. Différents systèmes supraconducteurs de lévitation et de propulsion seront décrits en examinant plus particulièrement l'aspect électromagnétique. Quelques programmes à travers le monde seront abordés. Les trains à sustentation magnétique pourraient constituer un nouveau mode de transport terrestre à vitesse élevée (500 km/h) pour le 21^e siècle. Les japonais n'ont cessé de s'intéresser à ce système avec bobine supraconductrice. Ils envisagent un stade préindustriel avec la construction d'une ligne de 43 km. En 1991 un programme américain pour une durée de six ans a été lancé pour évaluer les performances des systèmes à lévitation pour le transport aux Etats Unis. La MHD (Magnéto- Hydro-Dynamique) présente des avantages intéressants pour la propulsion navale et un regain d'intérêt apparaît à l'heure actuelle. Le japon se situe là encore à la pointe des d

  19. Recognition of a Nocardia transvalensis complex by resistance to aminoglycosides, including amikacin, and PCR-restriction fragment length polymorphism analysis.

    PubMed

    Wilson, R W; Steingrube, V A; Brown, B A; Blacklock, Z; Jost, K C; McNabb, A; Colby, W D; Biehle, J R; Gibson, J L; Wallace, R J

    1997-09-01

    Amikacin resistance, rare among nocardiae, was observed in 58 clinical isolates of nocardiae. All of these isolates hydrolyzed hypoxanthine, and 75 to 100% utilized citrate, D-galactose, and D-trehalose as sole carbon sources. Based on utilization of I-erythritol, D-glucitol, i-myo-inositol, D-mannitol, and ribitol and susceptibility to amoxicillin-clavulanic acid, the 58 isolates were separable into four groups. One group was negative for I-erythritol and ribitol and included all the isolates belonging to Nocardia asteroides complex antibiogram type IV. The remaining three groups were positive for I-erythritol and ribitol and were grouped within Nocardia transvalensis. The group that included the type strain was designated N. transvalensis sensu stricto, and the other two groups were designated new taxons 1 and 2. PCR-restriction fragment length polymorphism (RFLP) analysis of a 439-bp segment of the 65-kDa heat shock protein gene with XhoI and HinfI produced identical patterns for 53 (91%) and 58 (100%) isolates, respectively, and differentiated them from all other Nocardia taxa. NarI- and HaeIII-derived RFLP patterns clearly differentiated each of the four biochemically defined taxa. These four groups were also distinguishable by using the chromogenic substrates in Dade MicroScan test panels. By high-performance liquid chromatography, these isolates exhibited the same unique mycolic acid-ester elution patterns that differed from those of all other clinically significant nocardiae. Gas-liquid chromatographic analysis of fatty acids also produced similar patterns for all isolates that distinguished them from all other Nocardia taxa, but did not differentiate the four taxa within the complex. We propose the designation N. transvalensis complex for these four groups of nocardiae, pending further genetic evaluation.

  20. Integral Constraints and MHD Stability

    NASA Astrophysics Data System (ADS)

    Jensen, T. H.

    2003-10-01

    Determining stability of a plasma in MHD equilibrium, energetically isolated by a conducting wall, requires an assumption on what governs the dynamics of the plasma. One example is the assumption that the plasma obeys ideal MHD, leading to the well known ``δ W" criteria [I. Bernstein, et al., Proc. Roy. Soc. London A244, 17 (1958)]. A radically different approach was used by Taylor [J.B. Taylor, Rev. Mod. Phys. 58, 741 (1986)] in assuming that the dynamics of the plasma is restricted only by the requirement that helicity, an integral constant associated with the plasma, is conserved. The relevancy of Taylor's assumption is supported by the agreement between resulting theoretical results and experimental observations. Another integral constraint involves the canonical angular momentum of the plasma particles. One consequence of using this constraint is that tokamak plasmas have no poloidal current in agreement with some current hole tokamak observations [T.H. Jensen, Phys. Lett. A 305, 183 (2002)].

  1. Operational analysis of open-cycle MHD

    NASA Astrophysics Data System (ADS)

    Lippert, T. E.; McCutchan, D. A.

    1980-07-01

    Open cycle magnetohydrodynamic (OCMHD) conceptual power plant designs are studied in the context of a utility system to form a better basis for understanding their design, design requirements, and market possibilities. Based on assumed or projected plant costs and performance characteristics, assumed economics and escalation factors, and one coal supply and delivery scenario, overall and regional OCMHD utility market possibilities are reviewed. Additionally, for one hypothetical utility system a generation expansion plan is developed that includes OCMHD as a baseload power generating station. The impact on generation system economics and operation of alternating selected MHD plant cost and performance characteristics is reviewed. Baseload plant availability is shown as an important plant design consideration, and a general methodology and data base is developed to assess the impact on design and cost of various reliability decisions. An overall plant availability goal is set and the required availabilities of various MHD high technology components are derived to meet the plant goal. The approach is then extended to projecting channel life goals for various plant design configurations and assumptions.

  2. Stabilization of the external kink and other MHD issues. Summary report

    SciTech Connect

    Freidberg, J.P.; Goldston, R.J.; Jardin, S.C.; Neilson, G.H.; Rosenbluth, M.N.; Taylor, T.S.; Thomassen, K.I.

    1993-08-13

    An MHD workshop entitled ``Stabilization of the External Kink and Other MHD Issues`` was held June 1993. This is a summary report of activities at that workshop, structured to respond to the three questions in the charge (letter from J. Willis). The experimental and theoretical status of these issues, and the R&D needs in each area, are addressed. We discuss the potential impact on the TPX and ITER programs of these issues. The workshop participants came from a broad and diverse range of institutions in the fusion program, including international participants. As a result, we believe the summary here reflects some consensus of the community on these very important program issues, and that the TPX and ITER programs will benefit from these discussions. The title of the workshop was chosen to indicate both our knowledge and our uncertainty of MHD phenomena limiting {beta} and causing disruptions in tokamaks. The purpose was to bring together theorists and experimentalist in order to assess our current understanding of the external kink instability at high {beta}, and to assess the potential for passive or active stabilization of the dominant modes. We also outlined the R&D needed for TPX and other future devices. Not only was the preworkshop theory clearly presented, but significant new theoretical results were described for the first time, emphasizing the roles of the resistivity of the cold edge plasma and of the plasma toroidicity in the stability criteria. Excellent reviews of the effects of the vessel walls on plasma stability were given as related to the DIII-D, TFTR, JET, PBX-M, and HBT-EP experiments. These results are generally consistent with the more complete theory.

  3. Metal/gas MHD conversion

    NASA Astrophysics Data System (ADS)

    Thibault, J. P.; Joussellin, F.; Alemany, A.; Dupas, A.

    1982-09-01

    Operation features, theory, performance, and possible spatial applications of metal/gas MHD electrical generators are described. The working principle comprises an MHD channel, surrounded by a magnet, filled with a molten, highly conductive metal into which gas is pumped. The heat of the metal expands the gas, forcing a flow through the magnetic field crossing the channel, thus creating an electrical current conducted by the metal. The gas and metal are separated by a centrifugal device and both are redirected into the channel, forming thereby a double closed circuit when the heat of the molten metal is returned to the flow. Necessary characteristics for the gas such as a fairly low vaporization temperature and nonmiscibility with the metal, are outlined, and a space system using Li-Cs or Z-K as the heat carrier kept molten by a parabolic dish system is sketched. Equations governing the fluid mechanics, thermodynamics, and the electrical generation are defined. The construction of a prototype MHD generator using a tin-water flow operating at 250 C, a temperature suitable for coupling to solar heat sources, is outlined, noting expected efficiencies of 20-30 percent.

  4. 2D Numerical MHD Models of Solar Explosive Events

    NASA Astrophysics Data System (ADS)

    Roussev, I.

    2001-10-01

    Observations of the Sun reveal a great variety of dynamic phenomena interpretable as a manifestation of magnetic reconnection. These range from small-scale 'Explosive events' seen in the 'quiet' Sun, through violent flares observed in active regions. The high degree of complexity of the magnetic field inferred from observations may locally produce a fruitful environment for the process of magnetic reconnection to take place. Explosive events are associated with regions undergoing magnetic flux cancellation. This thesis presents a 2-dimensional (2D) numerical study devoted to explore the idea that the salient spectral signatures seen in explosive events are most probably caused by bi-directional outflow jets as a results of an ongoing magnetic reconnection. In order to provide qualitative results needed for the better physical interpretation of solar explosive events, several models intended to represent a 'quiet' Sun transition of solar explosive events, several models intended to represent a 'quiet' Sun transition region undergoing magnetic reconnection are examined, in both unstratified and gravitationally stratified atmospheres. The magnetic reconnection is initiated in an ad hoc manner, and the dynamic evolution is followed by numerically solving the equations of 2D dissipative magnetohydrodynamics (MHD), including the effects of field-aligned thermal conduction, radiative losses, volumetric heating, and anomalous resistivity.

  5. Ex Vivo Activity of Endoperoxide Antimalarials, Including Artemisone and Arterolane, against Multidrug-Resistant Plasmodium falciparum Isolates from Cambodia

    DTIC Science & Technology

    2014-10-01

    are urgently needed to address the ma-jor global public health problem of malaria . Despite contain- ment and control measures, malaria caused by...test wells (basal growth control ) to the OD for the well containing the maximum tested drug concentration. Molecular markers of malaria drug resistance...Extensive in vitro evidence suggests a role for pfmdr1 amplification in artemisinin resistance, such as indicated by a genetically modified P

  6. High-beta extended MHD simulations of stellarators

    NASA Astrophysics Data System (ADS)

    Bechtel, T. A.; Hegna, C. C.; Sovinec, C. R.; Roberds, N. A.

    2016-10-01

    The high beta properties of stellarator plasmas are studied using the nonlinear, extended MHD code NIMROD. In this work, we describe recent developments to the semi-implicit operator which allow the code to model 3D plasma evolution with better accuracy and efficiency. The configurations under investigation are an l=2, M=5 torsatron with geometry modeled after the Compact Toroidal Hybrid (CTH) experiment and an l=2, M=10 torsatron capable of having vacuum rotational transform profiles near unity. High-beta plasmas are created using a volumetric heating source and temperature dependent anisotropic thermal conduction and resistivity. To reduce computation expenses, simulations are initialized from stellarator symmetric pseudo-equilibria by turning on symmetry breaking modes at finite beta. The onset of MHD instabilities and nonlinear consequences are monitored as a function of beta as well as the fragility of the magnetic surfaces. Research supported by US DOE under Grant No. DE-FG02-99ER54546.

  7. Rapporteur report: MHD electric power plants

    NASA Technical Reports Server (NTRS)

    Seikel, G. R.

    1980-01-01

    Five US papers from the Proceedings of the Seventh International Conference on MHD Electrical Power Generation at the Massachusetts Institute of Technology are summarized. Results of the initial parametric phase of the US effort on the study of potential early commercial MHD plants are reported and aspects of the smaller commercial prototype plant termed the Engineering Test Facility are discussed. The alternative of using a disk geometry generator rather than a linear generator in baseload MHD plants is examined. Closed-cycle as well as open-cycle MHD plants are considered.

  8. System study of an MHD/gas turbine combined-cycle baseload power plant. HTGL report No. 134

    SciTech Connect

    Annen, K.D.

    1981-08-01

    The MHD/gas turbine combined-cycle system has been designed specifically for applications where the availability of cooling water is very limited. The base case systems which were studied consisted of an MHD plant with a gas turbine bottoming plant, and required no cooling water. The gas turbine plant uses only air as its working fluid and receives its energy input from the MHD exhaust gases by means of metal tube heat exchangers. In addition to the base case systems, vapor cycle variation systems were considered which included the addition of a vapor cycle bottoming plant to improve the thermal efficiency. These systems required a small amount of cooling water. The MHD/gas turbine systems were modeled with sufficient detail, using realistic component specifications and costs, so that the thermal and economic performance of the system could be accurately determined. Three cases of MHD/gas turbine systems were studied, with Case I being similar to an MHD/steam system so that a direct comparison of the performances could be made, with Case II being representative of a second generation MHD system, and with Case III considering oxygen enrichment for early commercial applications. The systems are nominally 800 MW/sub e/ to 1000 MW/sub e/ in size. The results show that the MHD/gas turbine system has very good thermal and economic performances while requiring either little or no cooling water. Compared to the MHD/steam system which has a cooling tower heat load of 720 MW, the Base Case I MHD/gas turbine system has a heat rate which is 13% higher and a cost of electricity which is only 7% higher while requiring no cooling water. Case II results show that an improved performance can be expected from second generation MHD/gas turbine systems. Case III results show that an oxygen enriched MHD/gas turbine system may be attractive for early commercial applications in dry regions of the country.

  9. Novel Plasmid-Borne Multidrug Resistance Gene Cluster Including lsa(E) from a Linezolid-Resistant Enterococcus faecium Isolate of Swine Origin

    PubMed Central

    Si, Hongbin; Zhang, Wan-Jiang; Chu, Shengbo; Wang, Xiu-Mei; Dai, Lei; Hua, Xin; Dong, Zhimin

    2015-01-01

    A novel nonconjugative plasmid of 28,489 bp from a porcine linezolid-resistant Enterococcus faecium isolate was completely sequenced. This plasmid harbored a novel type of multiresistance gene cluster that comprised the resistance genes lnu(B), lsa(E), spw, aadE, aphA3, and two copies of erm(B), which account for resistance to macrolides, lincosamides, streptogramins, pleuromutilins, streptomycin, spectinomycin, and kanamycin/neomycin. Structural comparisons suggested that this plasmid might have developed from other enterococcal plasmids by insertion element (IS)-mediated interplasmid recombination processes. PMID:26324271

  10. FLASH MHD simulations of experiments that study shock-generated magnetic fields

    NASA Astrophysics Data System (ADS)

    Tzeferacos, P.; Fatenejad, M.; Flocke, N.; Graziani, C.; Gregori, G.; Lamb, D. Q.; Lee, D.; Meinecke, J.; Scopatz, A.; Weide, K.

    2015-12-01

    We summarize recent additions and improvements to the high energy density physics capabilities in FLASH, highlighting new non-ideal magneto-hydrodynamic (MHD) capabilities. We then describe 3D Cartesian and 2D cylindrical FLASH MHD simulations that have helped to design and analyze experiments conducted at the Vulcan laser facility. In these experiments, a laser illuminates a carbon rod target placed in a gas-filled chamber. A magnetic field diagnostic (called a Bdot) employing three very small induction coils is used to measure all three components of the magnetic field at a chosen point in space. The simulations have revealed that many fascinating physical processes occur in the experiments. These include megagauss magnetic fields generated by the interaction of the laser with the target via the Biermann battery mechanism, which are advected outward by the vaporized target material but decrease in strength due to expansion and resistivity; magnetic fields generated by an outward expanding shock via the Biermann battery mechanism; and a breakout shock that overtakes the first wave, the contact discontinuity between the target material and the gas, and then the initial expanding shock. Finally, we discuss the validation and predictive science we have done for this experiment with FLASH.

  11. MHD simulations of DC helicity injection for current drive in tokamaks

    SciTech Connect

    Sovinec, C.R.; Prager, S.C.

    1994-12-01

    MHD computations of DC helicity injection in tokamak-like configurations show current drive with no ``loop voltage`` in a resistive, pressureless plasma. The self-consistently generated current profiles are unstable to resistive modes that partially relax the profile through the MHD dynamo mechanism. The current driven by the fluctuations leads to closed contours of average poloidal flux. However, the 1% fluctuation level is large enough to produce a region of stochastic magnetic field. A limited Lundquist number (S) scan from 2.5 {times} 10{sup 3} to 4 {times} 10{sup 4} indicates that both the fluctuation level and relaxation increase with S.

  12. Stability of the Halley Cometo-Sheath with Resistivity and Plasma Motion

    NASA Technical Reports Server (NTRS)

    Srivastava, K.

    1993-01-01

    The MHD stability of the cometary inner shealth determined by the balance between the inward Lorentz body force and the outward ion-neutral drag force is investigated by numerically solving the wave equations which include resistivity, plasma motion and plasma pressure with the help of two-point boundary value method.

  13. Coronal roots of solar wind streams: 3-D MHD modeling

    NASA Technical Reports Server (NTRS)

    Pisanko, Yu. V.

    1995-01-01

    Weak (discontinuous) solutions of the 3-D MHD equations look like a promising tool to model the transonic solar wind with structural elements: current sheets, coronal plumes etc. Using the observational information about various coronal emissions one can include these structural elements into the 3-D MHD solar wind model by embedding the discontinuities of given type. Such 3-D MHD structured solar wind is calculated self-consistently: variants are examined via numerical experiments. In particular, the behavior of coronal plumes in the transonic solar wind flow, is modeled. The input information for numerical modeling (for example, the magnetic field map at the very base of the solar corona) can be adjusted so that fast stream arises over the center of the coronal hole, over the coronal hole boundaries and, even, over the region with closed magnetic topology. 3-D MHD equations have the analytical solution which can serve as a model of supersonic trans-alfvenic solar wind in the (5-20) solar radii heliocentric distance interval. The transverse, nonradial total (gas + magnetic field) pressure balance in the flow is the corner-stone of this solution. The solution describes the filamentation (ray-like structure of the solar corona) and streaming (formation of high-speed streams with velocities up to 800 km/sec) as a consequence of the magnetic field spatial inhomogeneous structure and trans-alfvenic character of the flow. The magnetic field works in the model as a 'controller' for the solar wind streaming and filamentation.

  14. MHD Technology Transfer, Integration and Review Committee. Second semiannual status report, July 1988--March 1989

    SciTech Connect

    Not Available

    1989-10-01

    As part of the MHD Integrated Topping Cycle (ITC) project, TRW was given the responsibility to organize, charter and co-chair, with the Department of Energy (DOE), an MHD Technology Transfer, Integration and Review Committee (TTIRC). The Charter of the TTIRC, which was approved by the DOE in June 1988 and distributed to the committee members, is included as part of this Summary. As stated in the Charter, the purpose of this committee is to: (1) review all Proof-of-Concept (POC) projects and schedules in the national MHD program; to assess their compatibility with each other and the first commercial MHD retrofit plant; (2) establish and implement technology transfer formats for users of this technology; (3) identify interfaces, issues, and funding structures directly impacting the success of the commercial retrofit; (4) investigate and identify the manner in which, and by whom, the above should be resolved; and (5) investigate and assess other participation (foreign and domestic) in the US MHD Program. The DOE fiscal year 1989 MHD Program Plan Schedule is included at the end of this Summary. The MHD Technology Transfer, Integration and Review Committee`s activities to date have focused primarily on the ``technology transfer`` aspects of its charter. It has provided a forum for the dissemination of technical and programmatic information among workers in the field of MHD and to the potential end users, the utilities, by holding semi-annual meetings. The committee publishes this semi-annual report, which presents in Sections 2 through 11 capsule summaries of technical progress for all DOE Proof-of-Concept MHD contracts and major test facilities.

  15. Seawater is a reservoir of multi-resistant Escherichia coli, including strains hosting plasmid-mediated quinolones resistance and extended-spectrum beta-lactamases genes.

    PubMed

    Alves, Marta S; Pereira, Anabela; Araújo, Susana M; Castro, Bruno B; Correia, António C M; Henriques, Isabel

    2014-01-01

    The aim of this study was to examine antibiotic resistance (AR) dissemination in coastal water, considering the contribution of different sources of fecal contamination. Samples were collected in Berlenga, an uninhabited island classified as Natural Reserve and visited by tourists for aquatic recreational activities. To achieve our aim, AR in Escherichia coli isolates from coastal water was compared to AR in isolates from two sources of fecal contamination: human-derived sewage and seagull feces. Isolation of E. coli was done on Chromocult agar. Based on genetic typing 414 strains were established. Distribution of E. coli phylogenetic groups was similar among isolates of all sources. Resistances to streptomycin, tetracycline, cephalothin, and amoxicillin were the most frequent. Higher rates of AR were found among seawater and feces isolates, except for last-line antibiotics used in human medicine. Multi-resistance rates in isolates from sewage and seagull feces (29 and 32%) were lower than in isolates from seawater (39%). Seawater AR profiles were similar to those from seagull feces and differed significantly from sewage AR profiles. Nucleotide sequences matching resistance genes bla TEM, sul1, sul2, tet(A), and tet(B), were present in isolates of all sources. Genes conferring resistance to 3rd generation cephalosporins were detected in seawater (bla CTX-M-1 and bla SHV-12) and seagull feces (bla CMY-2). Plasmid-mediated determinants of resistance to quinolones were found: qnrS1 in all sources and qnrB19 in seawater and seagull feces. Our results show that seawater is a relevant reservoir of AR and that seagulls are an efficient vehicle to spread human-associated bacteria and resistance genes. The E. coli resistome recaptured from Berlenga coastal water was mainly modulated by seagulls-derived fecal pollution. The repertoire of resistance genes covers antibiotics critically important for humans, a potential risk for human health.

  16. Seawater is a reservoir of multi-resistant Escherichia coli, including strains hosting plasmid-mediated quinolones resistance and extended-spectrum beta-lactamases genes

    PubMed Central

    Alves, Marta S.; Pereira, Anabela; Araújo, Susana M.; Castro, Bruno B.; Correia, António C. M.; Henriques, Isabel

    2014-01-01

    The aim of this study was to examine antibiotic resistance (AR) dissemination in coastal water, considering the contribution of different sources of fecal contamination. Samples were collected in Berlenga, an uninhabited island classified as Natural Reserve and visited by tourists for aquatic recreational activities. To achieve our aim, AR in Escherichia coli isolates from coastal water was compared to AR in isolates from two sources of fecal contamination: human-derived sewage and seagull feces. Isolation of E. coli was done on Chromocult agar. Based on genetic typing 414 strains were established. Distribution of E. coli phylogenetic groups was similar among isolates of all sources. Resistances to streptomycin, tetracycline, cephalothin, and amoxicillin were the most frequent. Higher rates of AR were found among seawater and feces isolates, except for last-line antibiotics used in human medicine. Multi-resistance rates in isolates from sewage and seagull feces (29 and 32%) were lower than in isolates from seawater (39%). Seawater AR profiles were similar to those from seagull feces and differed significantly from sewage AR profiles. Nucleotide sequences matching resistance genes blaTEM, sul1, sul2, tet(A), and tet(B), were present in isolates of all sources. Genes conferring resistance to 3rd generation cephalosporins were detected in seawater (blaCTX-M-1 and blaSHV-12) and seagull feces (blaCMY-2). Plasmid-mediated determinants of resistance to quinolones were found: qnrS1 in all sources and qnrB19 in seawater and seagull feces. Our results show that seawater is a relevant reservoir of AR and that seagulls are an efficient vehicle to spread human-associated bacteria and resistance genes. The E. coli resistome recaptured from Berlenga coastal water was mainly modulated by seagulls-derived fecal pollution. The repertoire of resistance genes covers antibiotics critically important for humans, a potential risk for human health. PMID:25191308

  17. Disk diffusion antimicrobial susceptibility testing of members of the family Legionellaceae including erythromycin-resistant variants of Legionella micdadei.

    PubMed Central

    Dowling, J N; McDevitt, D A; Pasculle, A W

    1984-01-01

    Disk diffusion antimicrobial susceptibility testing of members of the family Legionellaceae was accomplished on buffered charcoal yeast extract agar by allowing the bacteria to grow for 6 h before placement of the disks, followed by an additional 42-h incubation period before the inhibitory zones were measured. This system was standardized by comparing the zone sizes with the MICs for 20 antimicrobial agents of nine bacterial strains in five Legionella species and of 19 laboratory-derived, erythromycin-resistant variants of Legionella micdadei. A high, linear correlation between zone size and MIC was found for erythromycin, trimethoprim, penicillin, ampicillin, carbenicillin, cephalothin, cefamandole, cefoxitin, moxalactam, chloramphenicol, vancomycin, and clindamycin. Disk susceptibility testing could be employed to screen Legionella isolates for resistance to any of these antimicrobial agents, of which only erythromycin is known to be efficacious in the treatment of legionellosis. With selected antibiotics, disk susceptibility patterns also appeared to accurately identify to the species level the legionellae. The range of the MICs of the legionellae for rifampin and the aminoglycosides was too small to determine whether the correlation of zone size with MIC was linear. However, laboratory-derived, high-level rifampin-resistant variants of L. micdadei demonstrated no inhibition zone around the rifampin disk, indicating that disk susceptibility testing would likely identify a rifampin-resistant clinical isolate. Of the antimicrobial agents tested, the only agents for which disk susceptibility testing was definitely not possible on buffered charcoal yeast extract agar were oxacillin, the tetracyclines, and the sulfonamides. PMID:6565706

  18. Observational Tests of Recent MHD Turbulence Perspectives

    NASA Astrophysics Data System (ADS)

    Ghosh, Sanjoy

    2001-06-01

    This grant seeks to analyze the Heliospheric Missions data to test current theories on the angular dependence (with respect to mean magnetic field direction) of magnetohydrodynamic (MHD) turbulence in the solar wind. Solar wind turbulence may be composed of two or more dynamically independent components. Such components include magnetic pressure-balanced structures, velocity shears, quasi-2D turbulence, and slab (Alfven) waves. We use a method, developed during the first two years of this grant, for extracting the individual reduced spectra of up to three separate turbulence components from a single spacecraft time series. The method has been used on ISEE-3 data, Pioneer Venus Orbiter, Ulysses, and Voyager data samples. The correlation of fluctuations as a function of angle between flow direction and magnetic-field direction is the focus of study during the third year.

  19. Observational Tests of Recent MHD Turbulence Perspectives

    NASA Technical Reports Server (NTRS)

    Ghosh, Sanjoy; Guhathakurta, M. (Technical Monitor)

    2001-01-01

    This grant seeks to analyze the Heliospheric Missions data to test current theories on the angular dependence (with respect to mean magnetic field direction) of magnetohydrodynamic (MHD) turbulence in the solar wind. Solar wind turbulence may be composed of two or more dynamically independent components. Such components include magnetic pressure-balanced structures, velocity shears, quasi-2D turbulence, and slab (Alfven) waves. We use a method, developed during the first two years of this grant, for extracting the individual reduced spectra of up to three separate turbulence components from a single spacecraft time series. The method has been used on ISEE-3 data, Pioneer Venus Orbiter, Ulysses, and Voyager data samples. The correlation of fluctuations as a function of angle between flow direction and magnetic-field direction is the focus of study during the third year.

  20. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-07-01

    This eighteenth quarterly technical progress report of the MHD Integrated Topping cycle Project presents the accomplishments during the period November 1, 1991 to January 31, 1992. The precombustor is fully assembled. Manufacturing of all slagging stage components has been completed. All cooling panels were welded in place and the panel/shell gap was filled with RTV. Final combustor assembly is in progress. The low pressure cooling subsystem (LPCS) was delivered to the CDIF. Second stage brazing issues were resolved. The construction of the two anode power cabinets was completed.

  1. Ceramic component for MHD electrode

    DOEpatents

    Marchant, David D.; Bates, Junior L.

    1981-01-01

    A ceramic component which exhibits electrical conductivity down to near room temperatures has the formula: Hf.sub.x In.sub.y A.sub.z O.sub.2 where x=0.1 to 0.4, y=0.3 to 0.6, z=0.1 to 0.4 and A is a lanthanide rare earth or yttrium. The component is suitable for use in the fabrication of MHD electrodes or as the current leadout portion of a composite electrode with other ceramic components.

  2. Ceramic components for MHD electrode

    DOEpatents

    Marchant, D.D.

    A ceramic component which exhibits electrical conductivity down to near room temperatures has the formula: Hf/sub x/In/sub y/A/sub z/O/sub 2/ where x = 0.1 to 0.4, y = 0.3 to 0.6, z = 0.1 to 0.4 and A is a lanthanide rare earth or yttrium. The component is suitable for use in the fabrication of MHD electrodes or as the current leadout portion of a composite electrode with other ceramic components.

  3. Global MHD model of the earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Wu, C. C.

    1983-01-01

    A global MHD model of the earth's magnetosphere is defined. An introduction to numerical methods for solving the MHD equations is given with emphasis on the shock-capturing technique. Finally, results concerning the shape of the magnetosphere and the plasma flows inside the magnetosphere are presented.

  4. Performance and flow characteristics of MHD seawater thruster

    SciTech Connect

    Doss, E.D.

    1990-01-01

    The main goal of the research is to investigate the effects of strong magnetic fields on the electrical and flow fields inside MHD thrusters. The results of this study is important in the assessment of the feasibility of MHD seawater propulsion for the Navy. To accomplish this goal a three-dimensional fluid flow computer model has been developed and applied to study the concept of MHD seawater propulsion. The effects of strong magnetic fields on the current and electric fields inside the MHD thruster and their interaction with the flow fields, particularly those in the boundary layers, have been investigated. The results of the three-dimensional computations indicate that the velocity profiles are flatter over the sidewalls of the thruster walls in comparison to the velocity profiles over the electrode walls. These nonuniformities in the flow fields give rise to nonuniform distribution of the skin friction along the walls of the thrusters, where higher values are predicted over the sidewalls relative to those over the electrode walls. Also, a parametric study has been performed using the three-dimensional MHD flow model to analyze the performance of continuous electrode seawater thrusters under different operating parameters. The effects of these parameters on the fluid flow characteristics, and on the thruster efficiency have been investigated. Those parameters include the magnetic field (10--20 T), thruster diameter, surface roughness, flow velocity, and the electric load factor. The results show also that the thruster performance improves with the strength of the magnetic field and thruster diameter, and the efficiency decreases with the flow velocity and surface roughness.

  5. EVIDENCE OF ACTIVE MHD INSTABILITY IN EULAG-MHD SIMULATIONS OF SOLAR CONVECTION

    SciTech Connect

    Lawson, Nicolas; Strugarek, Antoine; Charbonneau, Paul E-mail: strugarek@astro.umontreal.ca

    2015-11-10

    We investigate the possible development of magnetohydrodynamical instabilities in the EULAG-MHD “millennium simulation” of Passos and Charbonneau. This simulation sustains a large-scale magnetic cycle characterized by solar-like polarity reversals taking place on a regular multidecadal cadence, and in which zonally oriented bands of strong magnetic fields accumulate below the convective layers, in response to turbulent pumping from above in successive magnetic half-cycles. Key aspects of this simulation include low numerical dissipation and a strongly sub-adiabatic fluid layer underlying the convectively unstable layers corresponding to the modeled solar convection zone. These properties are conducive to the growth and development of two-dimensional instabilities that are otherwise suppressed by stronger dissipation. We find evidence for the action of a non-axisymmetric magnetoshear instability operating in the upper portions of the stably stratified fluid layers. We also investigate the possibility that the Tayler instability may be contributing to the destabilization of the large-scale axisymmetric magnetic component at high latitudes. On the basis of our analyses, we propose a global dynamo scenario whereby the magnetic cycle is driven primarily by turbulent dynamo action in the convecting layers, but MHD instabilities accelerate the dissipation of the magnetic field pumped down into the overshoot and stable layers, thus perhaps significantly influencing the magnetic cycle period. Support for this scenario is found in the distinct global dynamo behaviors observed in an otherwise identical EULAG-MHD simulations, using a different degree of sub-adiabaticity in the stable fluid layers underlying the convection zone.

  6. An MHD model of the earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Wu, C. C.

    1985-01-01

    It is pointed out that the earth's magnetosphere arises from the interaction of the solar wind with the earth's geomagnetic field. A global magnetohydrodynamics (MHD) model of the earth's magnetosphere has drawn much attention in recent years. In this model, MHD equations are used to describe the solar wind interaction with the magnetosphere. In the present paper, some numerical aspects of the model are considered. Attention is given to the ideal MHD equations, an equation of state for the plasma, the model as an initial- and boundary-value problem, the shock capturing technique, computational requirements and techniques for global MHD modeling, a three-dimensional mesh system employed in the global MHD model, and some computational results.

  7. MHD air heater technology development. Annual technical progress report, January 1, 1980-December 31, 1980

    SciTech Connect

    1981-03-01

    Progress on the technology development of the directly-fired high temperature air heater (HTAH) for MHD power plants is described in detail. The objective of task 1 is to continue development of ceramic materials technology for the directly-fired HTAH. The objectives of task 2 are to demonstrate the technical feasibility of operating a directly-fired HTAH (including both the heater matrix and valves), to continue obtaining information on life and corrosion resistance of HTAH materials, and to obtain design information for full-scale studies and future design work. The objectives of task 3 are to begin the identification of HTAH control requirements and control system needs, and to continue full-scale study efforts incorporating updated materials and design information in order to identify development needs for the HTAH development program. (WHK)

  8. Off-design performance analysis of MHD generator channels

    NASA Astrophysics Data System (ADS)

    Wilson, D. R.; Williams, T. S.

    1980-01-01

    A computer code for performing parametric design point calculations, and evaluating the off-design performance of MHD generators has been developed. The program is capable of analyzing Faraday, Hall, and DCW channels, including the effect of electrical shorting in the gas boundary layers and coal slag layers. Direct integration of the electrode voltage drops is included. The program can be run in either the design or off-design mode. Details of the computer code, together with results of a study of the design and off-design performance of the proposed ETF MHD generator are presented. Design point variations of pre-heat and stoichiometry were analyzed. The off-design study included variations in mass flow rate and oxygen enrichment.

  9. Toward 3D MHD modeling of neoclassical tearing mode suppression by ECCD

    NASA Astrophysics Data System (ADS)

    Pratt, J.; Westerhof, E.

    2012-09-01

    We propose a framework to extend the magnetohydrodynamic (MHD) equations to include electron cyclotron current drive (ECCD) and discuss previous models proposed by Giruzzi et al. [2] and by Hegna and Callen [3]. To model neoclassical tearing mode (NTM) instabilities and study the growth of magnetic islands as NTMs evolve, we employ the nonlinear reduced-MHD simulation JOREK. We present tearing-mode growth-rate calculations from JOREK simulations.

  10. A Review of the Possible Role of Constraints in MHD Turbulence

    NASA Astrophysics Data System (ADS)

    Pouquet, Annick

    2015-12-01

    The following sections are included: * Introduction * The context * The Kolmogorov law * The equations * What can we learn from statistical mechanics * Energy spectra * Weak MHD turbulence * When the weak regime breaks down * Intermittency * Exact laws * Explicit examples of non-universal behavior in MHD * The role of alignment between the velocity and the magnetic field * Can the dynamics of magnetic helicity play a role for energy scaling? * Can models help? * Conclusions * Acknowledgments * References

  11. Magnetohydrodynamics (MHD) Engineering Test Facility (ETF) 200 MWe power plant. Design Requirements Document (DRD)

    NASA Technical Reports Server (NTRS)

    Rigo, H. S.; Bercaw, R. W.; Burkhart, J. A.; Mroz, T. S.; Bents, D. J.; Hatch, A. M.

    1981-01-01

    A description and the design requirements for the 200 MWe (nominal) net output MHD Engineering Test Facility (ETF) Conceptual Design, are presented. Performance requirements for the plant are identified and process conditions are indicated at interface stations between the major systems comprising the plant. Also included are the description, functions, interfaces and requirements for each of these major systems. The lastest information (1980-1981) from the MHD technology program are integrated with elements of a conventional steam electric power generating plant.

  12. Feasibility of MHD submarine propulsion

    SciTech Connect

    Doss, E.D. ); Sikes, W.C. )

    1992-09-01

    This report describes the work performed during Phase 1 and Phase 2 of the collaborative research program established between Argonne National Laboratory (ANL) and Newport News Shipbuilding and Dry Dock Company (NNS). Phase I of the program focused on the development of computer models for Magnetohydrodynamic (MHD) propulsion. Phase 2 focused on the experimental validation of the thruster performance models and the identification, through testing, of any phenomena which may impact the attractiveness of this propulsion system for shipboard applications. The report discusses in detail the work performed in Phase 2 of the program. In Phase 2, a two Tesla test facility was designed, built, and operated. The facility test loop, its components, and their design are presented. The test matrix and its rationale are discussed. Representative experimental results of the test program are presented, and are compared to computer model predictions. In general, the results of the tests and their comparison with the predictions indicate that thephenomena affecting the performance of MHD seawater thrusters are well understood and can be accurately predicted with the developed thruster computer models.

  13. MHD Simulations: Corotating Interaction Regions

    NASA Astrophysics Data System (ADS)

    Wiengarten, T.; Kleimann, J.; Fichtner, H.; Kissmann, R.

    2014-09-01

    Corotating Interaction Regions (CIRs) form in the solar wind when parcels of fast-speed wind interact with slow-speed wind due to the rotation of the Sun. The resulting buildup of pressure generates disturbances that, with increasing time (or distance from the Sun), may develop into a so-called forward-reverse shock pair. During solar-quiet times CIRs can be the dominant force shaping large-scale structures in the heliosphere. Studying CIRs is therefore important because the associated shocks are capable of e.g. accelerating energetic particles or deflecting cosmic rays. The global structure of CIRs can be modeled with an MHD approach that gives the plasma quantities needed to model the transport of particles in the heliosphere with e.g. stochastic differential equations. Here, we show results from 3D-MHD simulations with our code CRONOS for a) analytic boundary conditions where results can be compared to those obtained with a different code and b) boundary conditions derived with the Wang-Sheeley-Arge model from observational data (WSO), which are compared to spacecraft observations.

  14. Development and Application of Predictive Tools for MHD Stability Limits in Tokamaks

    SciTech Connect

    Brennan, Dylan; Miller, G. P.

    2016-10-03

    This is a project to develop and apply analytic and computational tools to answer physics questions relevant to the onset of non-ideal magnetohydrodynamic (MHD) instabilities in toroidal magnetic confinement plasmas. The focused goal of the research is to develop predictive tools for these instabilities, including an inner layer solution algorithm, a resistive wall with control coils, and energetic particle effects. The production phase compares studies of instabilities in such systems using analytic techniques, PEST- III and NIMROD. Two important physics puzzles are targeted as guiding thrusts for the analyses. The first is to form an accurate description of the physics determining whether the resistive wall mode or a tearing mode will appear first as β is increased at low rotation and low error fields in DIII-D. The second is to understand the physical mechanism behind recent NIMROD results indicating strong damping and stabilization from energetic particle effects on linear resistive modes. The work seeks to develop a highly relevant predictive tool for ITER, advance the theoretical description of this physics in general, and analyze these instabilities in experiments such as ASDEX Upgrade, DIII-D, JET, JT-60U and NTSX. The awardee on this grant is the University of Tulsa. The research efforts are supervised principally by Dr. Brennan. Support is included for two graduate students, and a strong collaboration with Dr. John M. Finn of LANL. The work includes several ongoing collaborations with General Atomics, PPPL, and the NIMROD team, among others.

  15. [Genetic analysis of multidrug-resistant Streptococcus pneumoniae including meropenem resistance that was isolated from elderly residents with pneumonia in nursing-care facilities].

    PubMed

    Ota, Kazuko; Chiba, Naoko; Sato, Kentaro; Nara, Syoetu; Kato, Satoko; Kanazawa, Hisao; Ikejima, Shin; Takahashi, Yoshihiro; Iwata, Satoshi; Ubukata, Kimiko

    2014-07-01

    From February to December 20XX, penicillin-resistant Streptococcus pneumoniae (PRSP) showing MICs of 16-32 microg/mL to cefotaxime (CTX) and 4-8 microg/mL to meropenem (MEPM) were isolated from 6 patients hospitalized at the general hospital S (2 cases) and hospital A (4 cases), close to the hospital S. Five elderly patients among these six cases came from nursing care facilities or nursing care-related medical facilities. All elderly persons (mean age: 81.7 years) were diagnosed as having pneumonia at the time of admission and the problematic PRSP was isolated from sputum samples collected on admission. Notably, all of these PRSP isolates simultaneously showed high resistance to macrolide agents mediated by an erm (B) gene and to fluoroquinolone agents via mutations in the gyrA and parC genes. Eventually, they were identified as multidrug-resistant S. pneumoniae (MDRSP) with high resistance to many agents. The capsule type of all strains was serotype 19F and multilocus sequence typing (MLST) revealed that they belonged to clonal complex (CC) 7993, which has not been reported before. It was thus concluded that the MDRSP that had spread within the nursing facilities was transmitted to the general hospitals via the elderly inpatients with pneumonia caused by these agents. Although one case finally had a poor outcome, the pneumococcal infection was not the direct trigger of the event. The current ratio of MDRSP is concluded to be very low. However, general hospitals that accept patients for therapeutic purposes from nursing-care facilities have to share epidemiological information in a timely manner with the nursing homes to prevent nosocomial infections.

  16. Technical support for open-cycle MHD program. Progress report, January-June 1979

    SciTech Connect

    Bomkamp, D. H.

    1980-07-01

    The support program for open-cycle MHD at the Argonne National Laboratory consists of developing the analytical tools needed for investigation of the performance of the major components in the combined-cycle MHD/steam power system. The analytical effort is centered on the primary components of the system that are unique to MHD and, also, on the integration of these analytical models into a model of the entire power-producing system. The present project activities include modeling of the combustor, generator, seed deposition, and formation and decomposition of NO. Parametric studies were performed to evaluate the performance of the U-25B generator and to support the design of the US U-25B generator. Refinements and improvements to the MHD systems code and executive program are described.

  17. Technical support for open-cycle MHD program. Progress report, October-December 1979

    SciTech Connect

    Doss, E. D.

    1980-12-01

    The support program for open-cycle MHD at Argonne National Laboratory is developing the analytical tools needed to investigate the performance of the major components in the combined cycle MHD/steam power system. The analytical effort is centered on the primary components of the system that are unique to MHD and also on the integration of these analytical representations into a model of the entire power producing system. The present project activities include modeling of the combustor, MHD channel and diffuser, slag separator, radiant boiler and high-temperature air heater. In addition, these models are combined into a complete system model, which is, at present, capable of carrying out optimizations of the entire system relative to either thermodynamic efficiency or cost of electrical power. Progress is reported in detail.

  18. Flares and MHD Jets in Protostar

    NASA Astrophysics Data System (ADS)

    Hayashi, M.; Shibata, K.; Matsumoto, R.

    We present a magnetic reconnection model for hard X-ray emission and flare-like hard X-ray variabilities associated with protostars detected by ASCA. The energy released by protostellar flares is 102 - 105 times larger than solar flares. Moreover, the spectrum is harder. A new ingredient in protostellar flare is the existence of a protostellar disk which can twist the magnetic fields threading the protostellar disk. We carried out magnetohydrodynamic (MHD) simulations of the disk-star interaction. The closed magnetic loops connecting the central star and the disk are twisted by the rotation of the disk. In the presence of resistivity, magnetic reconnection takes place in the current sheet formed inside the expanding loops. Hot, outgoing plasmoid and post flare loops are formed as a result of the reconnection. Numerical results are consistent with the observed plasma temperature (107 - 108K), the length of the flaring loop (1011-1012cm), the total energy of X-ray flares (~1035-36erg). Furthermore, along the opening magnetic loops, hot jet is ejected in bipolar directions with speed 200-400 km/s. The speed and mass flow rate of the jet is consistent with those of optical jets. Our model can explain both the X-ray flare-like variability and mass outflow in star forming region.

  19. Activation of MHD reconnection on ideal timescales

    NASA Astrophysics Data System (ADS)

    Landi, S.; Papini, E.; Del Zanna, L.; Tenerani, A.; Pucci, F.

    2017-01-01

    Magnetic reconnection in laboratory, space and astrophysical plasmas is often invoked to explain explosive energy release and particle acceleration. However, the timescales involved in classical models within the macroscopic MHD regime are far too slow to match the observations. Here we revisit the tearing instability by performing visco-resistive two-dimensional numerical simulations of the evolution of thin current sheets, for a variety of initial configurations and of values of the Lunquist number S, up to 107. Results confirm that when the critical aspect ratio of S 1/3 is reached in the reconnecting current sheets, the instability proceeds on ideal (Alfvénic) macroscopic timescales, as required to explain observations. Moreover, the same scaling is seen to apply also to the local, secondary reconnection events triggered during the nonlinear phase of the tearing instability, thus accelerating the cascading process to increasingly smaller spatial and temporal scales. The process appears to be robust, as the predicted scaling is measured both in inviscid simulations and when using a Prandtl number P  =  1 in the viscous regime.

  20. MHD dynamo for the Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Bonfiglio, Daniele; Cappello, Susanna; Escande, Dominique Frank; Spizzo, Gianluca

    2006-10-01

    MHD modelling is believed to provide a good description of large scale dynamics of the Reversed Field Pinch. In particular, 3-dimensional nonlinear simulations in a simple visco-resistive approximation [see Cappello PPCF 2004 and references therein] display many features in reasonable agreement with experiments. In recent times it has been shown that the general and basic tendency of the RFP to develop a more or less regular global kink type deformation of the plasma column forces a corresponding charge separation (consistent with quasi-neutrality) and a related electrostatic field. The ensuing electrostatic drift velocity (nearly) coincides with the dynamo velocity field traditionally considered to sustain the configuration [Bonfiglio,Cappello,Escande PRL 2005; Cappello,Bonfiglio,Escande PHP 2006]. In this presentation we review our present understanding in this subject. In particular we focus on the description of the formation of pure helical laminar RFP solutions, and study the relationship between the electrostatic structure and the topological properties of the magnetic field in the case of the less regular turbulent solutions, where the robustness of a chain of magnetic islands isolating the chaotic core from the edge has been recently highlighted [Spizzo,Cappello, Cravotta, Escande, Predebon, Marrelli, Martin, White, PRL 2006].

  1. A three dimensional MHD model of the earth's magnetosphere

    NASA Technical Reports Server (NTRS)

    Wu, C. C.; Walker, R. J.; Dawson, J. M.

    1981-01-01

    The results of a global MHD calculation of the steady state solar wind interaction with a dipole magnetic field are presented. The computer code used, being much faster than previous codes, makes it possible to increase the number of grid points in the system by an order of magnitude. The resulting model qualitatively reproduces many of the observed features of the quiet time magnetosphere including the bow shock, magnetopause, and plasma sheet.

  2. MHD generator with improved network coupling electrodes to a load

    DOEpatents

    Rosa, Richard J.

    1977-01-01

    An MHD generator has a plurality of segmented electrodes extending longitudinally of a duct, whereby progressively increasing high DC voltages are derived from a set of cathode electrodes and progressively increasing low DC voltages are derived from a set of anode electrodes. First and second load terminals are respectively connected to the cathode and anode electrodes by separate coupling networks, each of which includes a number of SCR's and a number of diode rectifiers.

  3. MHD channel development, part 2

    NASA Astrophysics Data System (ADS)

    1989-12-01

    This is the final report of work performed by Avco Research Laboratory, Inc. for the U.S. Department of Energy, Pittsburgh Energy Technology Center. The overall objectives of this program were: to contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at the 50 MW(sub th) and ultimately at commercial sizes; and to design and fabricate specific hardware items to be tested at a site to be specified by DOE. The program consisted of a series of related tasks, which are described in subsequent sections of this report. Section 2.0 summarizes the important results of the entire program.

  4. Equilibrium and global MHD stability study of KSTAR high beta plasmas under passive and active mode control

    NASA Astrophysics Data System (ADS)

    Katsuro-Hopkins, O.; Sabbagh, S. A.; Bialek, J. M.; Park, H. K.; Bak, J. G.; Chung, J.; Hahn, S. H.; Kim, J. Y.; Kwon, M.; Lee, S. G.; Yoon, S. W.; You, K.-I.; Glasser, A. H.; Lao, L. L.

    2010-02-01

    The Korea Superconducting Tokamak Advanced Research, KSTAR, is designed to operate a steady-state, high beta plasma while retaining global magnetohydrodynamic (MHD) stability to establish the scientific and technological basis of an economically attractive fusion reactor. An equilibrium model is established for stability analysis of KSTAR. Reconstructions were performed for the experimental start-up scenario and experimental first plasma operation using the EFIT code. The VALEN code was used to determine the vacuum vessel current distribution. Theoretical high beta equilibria spanning the expected operational range are computed for various profiles including generic L-mode and DIII-D experimental H-mode pressure profiles. Ideal MHD stability calculations of toroidal mode number of unity using the DCON code shows a factor of 2 improvement in the wall-stabilized plasma beta limit at moderate to low plasma internal inductance. The planned stabilization system in KSTAR comprises passive stabilizing plates and actively cooled in-vessel control coils (IVCCs) designed for non-axisymmetric field error correction and stabilization of slow timescale MHD modes including resistive wall modes (RWMs). VALEN analysis using standard proportional gain shows that active stabilization near the ideal wall limit can be reached with feedback using the midplane segment of the IVCC. The RMS power required for control using both white noise and noise taken from NSTX active stabilization experiments is computed for beta near the ideal wall limit. Advanced state-space control algorithms yield a factor of 2 power reduction assuming white noise while remaining robust with respect to variations in plasma beta.

  5. A study of runaway electron confinement and theory of neoclassical MHD turbulence

    SciTech Connect

    Kwon, Oh Jin

    1989-07-01

    This thesis consists of two major studies: a study of runaway electron confinement and a theory of neoclassical MHD turbulence. The aim of the former is to study the structure of internal magnetic turbulence in tokamaks, which is thought by many to be responsible for the heat transport. The aim of the latter is to extend existing theories of MHD turbulence in tokamaks into experimentally relevant low-collisionality regimes. This section contains a theory of neoclassical pressure-gradient-driven turbulence and a theory of neoclassical resistivity-gradient-driven turbulence.

  6. Comparison of four methods, including semi-automated rep-PCR, for the typing of vancomycin-resistant Enterococcus faecium.

    PubMed

    Bourdon, Nancy; Lemire, Astrid; Fines-Guyon, Marguerite; Auzou, Michel; Périchon, Bruno; Courvalin, Patrice; Cattoir, Vincent; Leclercq, Roland

    2011-01-01

    We have assessed the performance of semi-automated rep-PCR (Diversilab®) and multilocus sequence typing (MLST) in comparison to pulsed-field gel electrophoresis (PFGE) for typing a collection of 29 epidemiologically characterized vancomycin-resistant Enterococcus faecium (VRE). Sixteen strains that harbored the Tn1546 element were typed by PCR mapping. The discriminative power of the typing methods was calculated by the Simpson's index of diversity, and the concordance between methods was evaluated by the Kendall's coefficient of concordance. Semi-automated rep-PCR appeared as discriminative as PFGE and was further compared with PFGE for typing 67 VRE isolated during a hospital outbreak. Rep-PCR appeared to be more discriminative than PFGE for this second set of strains. Reproducibility of DiversiLab® was also tested against 35 selected isolates. Only three showed less than 97% similarity, indicating high reproducibility at this level of discrimination. In conclusion, semi-automated rep-PCR is a useful tool for rapid screening of VRE isolates during an outbreak, although cost of the system may be limiting for routine implementation. PFGE, which remains the reference method, should be used for confirmation and evaluation of the genetic relatedness of epidemic isolates.

  7. Linear MHD Stability Analysis of the SSPX Spheromak

    NASA Astrophysics Data System (ADS)

    Jayakumar, R.; Cohen, B. I.; Hooper, E. B.; Lodestro, L. L.; McLean, H. S.; Pearlstein, L. D.; Wood, R.; Turnbull, A. D.; Sovinec, C.

    2007-11-01

    Good correlation between the toroidal mode numbers of measured magnetic fluctuations in high temperature SSPX plasmas and presence of low-order rational surfaces in the reconstructed q profiles, suggests that the quality of magnetic surfaces in SSPX is sufficiently good for applying standard linear MHD stability analyses. Previously we have reported on benchmarking the code NIMROD against GATO, with good agreement in growth rates for ideal-MHD internal kinks and an external kinks with no current on open field lines (for equilibria imported from the code Corsica). Recent stability analyses also show that presence of low order rational surfaces causes internal modes to become unstable. We will report on the progress in applying these tools for assessing beta limits in SSPX, using NIMROD analyses including current on open field lines and for comparison with experiments.

  8. Towards an MHD Theory for the Standoff Distance of Earth's Bow Shock

    NASA Technical Reports Server (NTRS)

    Carins, Iver H.; Grabbe, Crockett L.

    1994-01-01

    A magnetohydrodynamic (MHD) theory is developed for the standoff distance a(s) of the bow shock and the thickness Delta(ms) of the magnetosheath, using the empirical Spreiter et al. relation Delta(ms) = kX and the MHD density ratio X across the shock. The theory includes as special cases the well-known gasdynamic theory and associated phenomenological MHD-like models for Delta(ms) and As. In general, however, MHD effects produce major differences from previous models, especially at low Alfev (Ma) and Sonic (Ms) Mach numbers. The magnetic field orientation Ma, Ms and the ratio of specific heats gamma are all important variables of the theory. In contrast, the fast mode Mach number need play no direct role. Three principle conclusions are reached. First the gasdynamic and phenomenological models miss important dependences of field orientation and Ms generally provide poor approximations to the MHD results. Second, changes in field orientation and Ms are predicted to cause factor of approximately 4 changes in Delta(ms) at low Ma. These effects should be important when predicting the shock's location or calculating gramma from observations. Third, using Spreiter et al.'s value for k in the MHD theory leads to maxima a(s) values at low Ma and nominal Ms that are much smaller than observations and MHD simulations require. Resolving this problem requires either the modified Spreiter-like relation and larger k found in recent MHD simulations and/or a breakdown in the Spreiter-like relation at very low Ma.

  9. Towards an MHD theory for the standoff distance of Earth's bow shock

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.; Grabbe, Crockett L.

    1994-01-01

    An MHD theory is developed for the stand-off distance a(sub s) of the bow shock and the thickness delta(sub ms) of the magnetosheath, using the empirical Spreiter et al. relation delta(sub ms) = kX and the MHD density ratio X across the shock. The theory includes as special cases the well-known gasdynamic theory and associated phenomenological MHD-like models for delta(sub ms) and a(sub s). In general, however, MHD effects produce major differences from previous models, especially at low Alfven (M(sub A)) and sonic (M(sub S)) Mach numbers. The magnetic field orientation, M(sub A), M(sub S) and the ratio of specific heats gamma are all important variables of the theory. Three principal conclusions are reached. First, the gasdynamic and phenomenological models miss important dependances on field orientation and M(sub S) and generally provide poor approximations to the MHD results. Second, changes in field orientation and M(sub S) are predicted to cause factor of approximately 4 changes in delta(sub ms) at low M(sub A). Third, using Spreiter et al.'s value for k in the MHD theory leads to maximum a(sub s) values at low M(sub A) and nominal M(sub S) that are much smaller than observations and MHD simulations require. Resolving this problem requires either the modified Spreiter-like relation and larger k found in recent MHD simulations and/or breakdown in the Spreiter-like relation at very low M(sub A).

  10. Validation of EFIT++ MHD Equilibrium Reconstructions on DIII-D

    NASA Astrophysics Data System (ADS)

    Cornille, B.; Lanctot, M. J.; Lao, L. L.; Appel, L. C.; Meneghini, O.; Holcomb, C. T.

    2013-10-01

    MHD force balance calculations play a key role in the optimization of transport and stability in tokamaks. In high confinement tokamak plasmas, reconstructions of the MHD plasma equilibrium are needed to resolve key profile features including the edge pressure pedestal and resulting bootstrap current. The EFIT code is the standard tool for calculating MHD force balance in DIII-D and many tokamaks. This code has recently been rebuilt to be machine-independent in order to facilitate cross-machine comparisons. This update, EFIT++, is in its late stages of development and requires validation for widespread use. Benchmarking of EFIT++ against the established EFIT cases including motional Stark effect measurements from DIII-D will be presented. Work supported by the the National Undergraduate Fellowship Program in Plasma Physics and Fusion Energy Sciences and the US Department of Energy under DE-FC02-04ER54698, DE-AC05-06OR23100 and DE-AC52-07NA27344.

  11. MHD simulation of RF current drive in MST

    SciTech Connect

    Hendries, E. R.; Anderson, J. K.; Forest, C. B.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.; Diem, S.; Harvey, R. W.

    2014-02-12

    Auxiliary heating and current drive using RF waves such as the electron Bernstein wave (EBW) promises to advance the performance of the reversed field pinch (RFP). In previous computational work [1], a hypothetical edge-localized current drive is shown to suppress the tearing activity which governs the macroscopic transport properties of the RFP. The ideal conditions for tearing stabilization include a reduced toroidal induction, and precise width and radial position of the Gaussian-shaped external current drive. In support of the EBW experiment on the Madison Symmetric Torus, an integrated modeling scheme now incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ∼ 10{sup 4}) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ∼ 3×10{sup 6}) show unexpected results. The effect on nonlinearly saturated current profile by a particular RF-driven external force decreases in magnitude and widens considerably as the Lundquist number increases toward experimental values. Simulations reproduce the periodic current profile relaxation events observed in experiment (sawteeth) in the absence of current profile control. Reduction of the tearing mode amplitudes is still observable; however, reduction is limited to periods between the large bursts of magnetic activity at each sawtooth. The sawtoothing pattern persists with up to 10 MW of externally applied RF power. Periods with prolonged low tearing amplitude are predicted with a combination of external current drive and a reduced toroidal loop voltage, consistent with previous conclusions. Finally, the resistivity profile is observed to have a strong effect on the optimal externally driven current profile for mode stabilization.

  12. MHD simulation of RF current drive in MST

    NASA Astrophysics Data System (ADS)

    Hendries, E. R.; Anderson, J. K.; Diem, S.; Forest, C. B.; Harvey, R. W.; Reusch, J. A.; Seltzman, A. H.; Sovinec, C. R.

    2014-02-01

    Auxiliary heating and current drive using RF waves such as the electron Bernstein wave (EBW) promises to advance the performance of the reversed field pinch (RFP). In previous computational work [1], a hypothetical edge-localized current drive is shown to suppress the tearing activity which governs the macroscopic transport properties of the RFP. The ideal conditions for tearing stabilization include a reduced toroidal induction, and precise width and radial position of the Gaussian-shaped external current drive. In support of the EBW experiment on the Madison Symmetric Torus, an integrated modeling scheme now incorporates ray tracing and Fokker-Plank predictions of auxiliary current into single fluid MHD. Simulations at low Lundquist number (S ˜ 104) generally agree with the previous work; significantly more burdensome simulations at MST-like Lundquist number (S ˜ 3×106) show unexpected results. The effect on nonlinearly saturated current profile by a particular RF-driven external force decreases in magnitude and widens considerably as the Lundquist number increases toward experimental values. Simulations reproduce the periodic current profile relaxation events observed in experiment (sawteeth) in the absence of current profile control. Reduction of the tearing mode amplitudes is still observable; however, reduction is limited to periods between the large bursts of magnetic activity at each sawtooth. The sawtoothing pattern persists with up to 10 MW of externally applied RF power. Periods with prolonged low tearing amplitude are predicted with a combination of external current drive and a reduced toroidal loop voltage, consistent with previous conclusions. Finally, the resistivity profile is observed to have a strong effect on the optimal externally driven current profile for mode stabilization.

  13. Applying MHD Results to a Scramjet Vehicle

    DTIC Science & Technology

    2007-02-12

    1194, Reno, NV, January 2005. 10. Rosa, R.J., "Magnetohydrodynamic Energy Conversion", Hemisphere Publishing Corp., New York, 1968, Revised Printing ...Introduction and Background Projects Analytical and experimental studies of both electrohydrodynamic (EHD) and magnetohydrodynamic (MHD) application to...Institute, Tullahoma, TN, June 1981. 26. Vendell, E.W., "Free- Jet Electrical Conductivity Profiles of a Seeded MHD Combustion Plasma", 15"’ Symposium

  14. MHD Instabilities in Simple Plasma Configuration

    DTIC Science & Technology

    1984-01-01

    cause the field lines to break and reconnect. . This work is divided into two parts. Chapters " describe linear theory and Chapters -XV- describe the...details in any non- linear theory can rapidly mushroom out of all proportion. For this reason much work in nonlinear MHD theory is done by numerical...99 IX. INSTABILITIES IN A TOROIDAL PLASMA ........................ 125 X. QUASI- LINEAR THEORY OF MHD INSTABILITIES ........... 133

  15. Solar driven liquid metal MHD power generator

    NASA Technical Reports Server (NTRS)

    Lee, J. H.; Hohl, F. (Inventor)

    1983-01-01

    A solar energy collector focuses solar energy onto a solar oven which is attached to a mixer which in turn is attached to the channel of a MHD generator. Gas enters the oven and a liquid metal enters the mixer. The gas/liquid metal mixture is heated by the collected solar energy and moves through the MHD generator thereby generating electrical power. The mixture is then separated and recycled.

  16. Genomic markers of panitumumab resistance including ERBB2/ HER2 in a phase II study of KRAS wild-type (wt) metastatic colorectal cancer (mCRC).

    PubMed

    Barry, Garrett S; Cheang, Maggie C; Chang, Hector Li; Kennecke, Hagen F

    2016-04-05

    A prospective study was conducted to identify biomarkers associated with resistance to panitumumab monotherapy in patients with metastatic colorectal cancer (mCRC). Patients with previously treated, codon 12/13 KRAS wt, mCRC were prospectively administered panitumumab 6 mg/kg IV q2weeks. Of 34 panitumumab-treated patients, 11 (32%) had progressive disease at 8 weeks and were classified as non-responders. A Nanostring nCounter-based assay identified a 5-gene expression signature (ERBB2, MLPH, IRX3, MYRF, and KLK6) associated with panitumumab resistance (P = 0.001). Immunohistochemistry and in situ hybridization determined that the HER2 (ERBB2) protein was overexpressed in 4/11 non-responding and 0/21 responding cases (P = 0.035). Two non-responding tumors had ERBB2 gene amplification only, and one demonstrated both ERBB2 amplification and mutation. A non-codon 12/13 KRAS mutation occurred in one panitumumab-resistant patient and was mutually exclusive with ERBB2/HER2 abnormalities. This study identifies a 5-gene signature associated with non-response to single agent panitumumab, including a subgroup of non-responders with evidence of aberrant ERBB2/HER2 signaling. KRAS wt tumors resistant to EGFRi may be identified by gene signature analysis, and the HER2 pathway plays an important role in resistance to therapy.

  17. MHD heat and seed recovery technology project

    SciTech Connect

    Petrick, M.; Johnson, T. R.

    1980-08-01

    The MHD Heat and Seed Recovery Technology Project at Argonne National Laboratory is obtaining information for the design and operation of the steam plant downstream of the MHD channel-diffuser, and of the seed regeneration process. The project goal is to supply the engineering data required in the design of components for prototype and demonstration MHD facilities. The work is being done in close cooperation with the Heat Recovery-Seed Recovery facility, which will be a 20-MW pilot plant of the MHD steam bottoming system. The primary effort of the HSR Technology Project is directed toward experimental investigations of critical issues, such as 1) NO/sub x/ behavior in the radiant boiler and secondary combustor; 2) radiant boiler design to meet the multiple requirements of steam generation, NO/sub x/ decomposition, and seed slag separation; 3) effects of solid or liquid seed deposits on heat transfer and gas flow in the steam and air heaters; 4) formation, growth, and deposition of seed-slag particles, 5) character of the combustion gas effluents, and 6) the corrosion and erosion of ceramic and metallic materials of construction. These investigations are performed primarily in a 2-MW test facility, Argonne MHD Process Engineering Laboratory (AMPEL). Other project activities are related to studies of the thermochemistry of the seed-slag combustion gas system, identification of ceramic and metallic materials for service in the MHD-steam plant, and evaluation of seed regeneration processes. Progress is reported.

  18. Control of linear modes in cylindrical resistive magnetohydrodynamics with a resistive wall, plasma rotation, and complex gain

    SciTech Connect

    Brennan, D. P.; Finn, J. M.

    2014-10-15

    Feedback stabilization of magnetohydrodynamic (MHD) modes in a tokamak is studied in a cylindrical model with a resistive wall, plasma resistivity, viscosity, and toroidal rotation. The control is based on a linear combination of the normal and tangential components of the magnetic field just inside the resistive wall. The feedback includes complex gain, for both the normal and for the tangential components, and it is known that the imaginary part of the feedback for the former is equivalent to plasma rotation [J. M. Finn and L. Chacon, Phys. Plasmas 11, 1866 (2004)]. The work includes (1) analysis with a reduced resistive MHD model for a tokamak with finite β and with stepfunction current density and pressure profiles, and (2) computations with a full compressible visco-resistive MHD model with smooth decreasing profiles of current density and pressure. The equilibria are stable for β = 0 and the marginal stability values β{sub rp,rw} < β{sub rp,iw} < β{sub ip,rw} < β{sub ip,iw} (resistive plasma, resistive wall; resistive plasma, ideal wall; ideal plasma, resistive wall; and ideal plasma, ideal wall) are computed for both models. The main results are: (a) imaginary gain with normal sensors or plasma rotation stabilizes below β{sub rp,iw} because rotation suppresses the diffusion of flux from the plasma out through the wall and, more surprisingly, (b) rotation or imaginary gain with normal sensors destabilizes above β{sub rp,iw} because it prevents the feedback flux from entering the plasma through the resistive wall to form a virtual wall. A method of using complex gain G{sub i} to optimize in the presence of rotation in this regime with β > β{sub rp,iw} is presented. The effect of imaginary gain with tangential sensors is more complicated but essentially destabilizes above and below β{sub rp,iw}.

  19. Extraintestinal Pathogenic and Antimicrobial-Resistant Escherichia coli, Including Sequence Type 131 (ST131), from Retail Chicken Breasts in the United States in 2013.

    PubMed

    Johnson, James R; Porter, Stephen B; Johnston, Brian; Thuras, Paul; Clock, Sarah; Crupain, Michael; Rangan, Urvashi

    2017-03-15

    Chicken meat products are hypothesized to be vehicles for transmitting antimicrobial-resistant and extraintestinal pathogenic Escherichia coli (ExPEC) to consumers. To reassess this hypothesis in the current era of heightened concerns about antimicrobial use in food animals, we analyzed 175 chicken-source E. coli isolates from a 2013 Consumer Reports national survey. Isolates were screened by PCR for ExPEC-defining virulence genes. The 25 ExPEC isolates (12% of 175) and a 2:1 randomly selected set of 50 non-ExPEC isolates were assessed for their phylogenetic/clonal backgrounds and virulence genotypes for comparison with their resistance profiles and the claims on the retail packaging label ("organic," "no antibiotics," and "natural"). Compared with the findings for non-ExPEC isolates, the group of ExPEC isolates had a higher prevalence of phylogroup B2 isolates (44% versus 4%; P < 0.001) and a lower prevalence of phylogroup A isolates (4% versus 30%; P = 0.001), a higher prevalence of multiple individual virulence genes, higher virulence scores (median, 11 [range, 4 to 16] versus 8 [range, 1 to 14]; P = 0.001), and higher resistance scores (median, 4 [range, 0 to 8] versus 3 [range, 0 to 10]; P < 0.001). All five isolates of sequence type 131 (ST131) were ExPEC (P = 0.003), were as extensively resistant as the other isolates tested, and had higher virulence scores than the other isolates tested (median, 12 [range, 11 to 13] versus 8 [range, 1 to 16]; P = 0.005). Organic labeling predicted lower resistance scores (median, 2 [range, 0 to 3] versus 4 [range, 0 to 10]; P = 0.008) but no difference in ExPEC status or virulence scores. These findings document a persisting reservoir of extensively antimicrobial-resistant ExPEC isolates, including isolates from ST131, in retail chicken products in the United States, suggesting a potential public health threat.IMPORTANCE We found that among Escherichia coli isolates from retail chicken meat products purchased across the

  20. Effects of water molecules of Ar-Cs MHD disk generator operated with strong MHD interaction

    SciTech Connect

    Ishikawa, M.; Kosugi, A.; Inui, Y.; Kabashima, S.

    1998-07-01

    Effects of water molecule impurity are studied on performance of a disk type MHD generator operated with Ar-Cs weakly ionized plasma. To reveal phenomena for a wide range of operation conditions, time-dependent one-dimensional analyses are carried out, where an up-wind, second order Chakravarthy TVD scheme is applied for the gasdynamics, while a Galerkin FEM is used for the electrodynamics. A simplified model is used for the water molecule impurity, where total effects of nonelastic collision between electrons and water molecules are estimated by the collision loss factor of electrons and also the electron momentum-transfer collision frequency is taken into account. The collision loss factor of electrons and the electron momentum-transfer collision frequency are taken from references, and the loss factor is assumed to be 700 independently of the electron temperature. On the Fuji-1 facilities at Tokyo Institute Technology, Japan, series of experiment A4105 were carried out with the Disk F-4 generator. Ar was heated with the heat-exchanger heated by the natural gas-air combustion and the metal cesium was used as the seeding material, while SCM maintained the magnetic field of 4.7 T at the center of disk and the very strong MHD interaction was realized. The thermal input was about 3 MW, the electrical output was about 500 kW with the enthalpy extraction ratio of about 17%. The numerical analyses have shown that the water molecule enhances the ionization instability at the low voltage loading because of insufficient Joule heating for electrons. The generator performance is degraded and the strong MHD interaction between the unstable plasma and the flow field induces slow and fast moving shock waves, leading to the very complicated flow field. The fast and slow moving shocks collide with each other, merge into a sharp shock moving downward, and then the shock front moves back slightly to maintain the pressure balance, collides again with another weak moving shock, and

  1. Spontaneous Reconnection Onset in the Magnetotail: Kinetic and MHD Pictures

    NASA Astrophysics Data System (ADS)

    Sitnov, M. I.; Merkin, V. G.

    2014-12-01

    The mechanism of the reconnection onset in planetary magnetotails has been a topic of hot debate for more than three decades. At the kinetic level of description the key problem is a seemingly universal stability of the collisionless tearing mode when electrons are magnetized by the magnetic field normal to the current sheet. This effect can be eliminated in 2D equilibria with magnetic flux accumulated at the anti-sunward end of the tail. However, the resulting instability seen in 2D PIC simulations with open boundaries differs from the classical tearing mode because its main effect is the formation of dipolarization fronts, i. e., regions of an enhanced normal magnetic field rather than the reversal of its sign. Strong tailward gradients of the normal magnetic field characteristic of fronts suggest that they can be destroyed in 3D by buoyancy and flapping instabilities. However, 3D PIC simulations show that buoyancy and flapping motions can neither destroy nor change critically the near-2D picture of the front evolution, although they do significantly disturb it. Modeling and understanding of this kinetic picture of the reconnection onset in MHD terms is critically important for incorporating the explosive reconnection physics into global models of the magnetosphere and solar corona. A key to this has become the recognition that tail current sheets with accumulated flux regions can also be unstable with respect to an ideal analog of the tearing mode, which has a similar structure of the electromagnetic field and plasma perturbations but preserves the original magnetic field topology. MHD simulations with high Lundquist number confirm the existence of such "pseudo-tearing" instability regimes. Non-MHD effects, including different motions of electron and ion species as well as the ion Landau dissipation transform these ideal MHD motions into the tearing/slippage instability obtained in PIC simulations.

  2. Extended MHD Modeling of Tearing-Driven Magnetic Relaxation

    NASA Astrophysics Data System (ADS)

    Sauppe, Joshua

    2016-10-01

    Driven plasma pinch configurations are characterized by the gradual accumulation and episodic release of free energy in discrete relaxation events. The hallmark of this relaxation in a reversed-field pinch (RFP) plasma is flattening of the parallel current density profile effected by a fluctuation-induced dynamo emf in Ohm's law. Nonlinear two-fluid modeling of macroscopic RFP dynamics has shown appreciable coupling of magnetic relaxation and the evolution of plasma flow. Accurate modeling of RFP dynamics requires the Hall effect in Ohm's law as well as first order ion finite Larmor radius (FLR) effects, represented by the Braginskii ion gyroviscous stress tensor. New results find that the Hall dynamo effect from < J × B > / ne can counter the MHD effect from - < V × B > in some of the relaxation events. The MHD effect dominates these events and relaxes the current profile toward the Taylor state, but the opposition of the two dynamos generates plasma flow in the direction of equilibrium current density, consistent with experimental measurements. Detailed experimental measurements of the MHD and Hall emf terms are compared to these extended MHD predictions. Tracking the evolution of magnetic energy, helicity, and hybrid helicity during relaxation identifies the most important contributions in single-fluid and two-fluid models. Magnetic helicity is well conserved relative to the magnetic energy during relaxation. The hybrid helicity is dominated by magnetic helicity in realistic low-beta pinch conditions and is also well conserved. Differences of less than 1 % between magnetic helicity and hybrid helicity are observed with two-fluid modeling and result from cross helicity evolution through ion FLR effects, which have not been included in contemporary relaxation theories. The kinetic energy driven by relaxation in the computations is dominated by velocity components perpendicular to the magnetic field, an effect that had not been predicted. Work performed at

  3. Three-dimensional parametric study for MHD marine propulsion

    SciTech Connect

    Doss, E.D. ); Roy, G.D. )

    1990-01-01

    The performance of MHD seawater thrusters have been investigated using a three-dimensional MHD flow model. The model incorporates the interaction between the flow fields and the electrical fields inside the thruster. A parametric study has been performed using the three-dimensional MHD flow model to analyze the performance of continuous electrode seawater thrusters under different operating parameters. The effects of these parameters on the fluid flow characteristics, and on the thruster efficiency have been investigated. Those parameters include the magnetic field (10--20 T), thruster diameter (1--2 m), surface roughness (0--2 mm), flow velocity (5--30 m/s), and the electric load factor (1--10). The results of the three-dimensional computations indicate that the velocity profiles are flatter over the sidewalls in comparison to the velocity profiles over the electrode walls. However such differences are not significant. The results of the parametric study show that the thruster electrical efficiency increases with the strength of the magnetic field and thruster diameter, and decreases with the flow velocity and surface roughness. 8 refs, 8 figs., 1 tab.

  4. MHD magnet technology development program summary, September 1982

    SciTech Connect

    Not Available

    1983-11-01

    The program of MHD magnet technology development conducted for the US Department of Energy by the Massachusetts Institute of Technology during the past five years is summarized. The general strategy is explained, the various parts of the program are described and the results are discussed. Subjects covered include component analysis, research and development aimed at improving the technology base, preparation of reference designs for commercial-scale magnets with associated design evaluations, manufacturability studies and cost estimations, the detail design and procurement of MHD test facility magnets involving transfer of technology to industry, investigations of accessory subsystem characteristics and magnet-flow-train interfacing considerations and the establishment of tentative recommendations for design standards, quality assurance procedures and safety procedures. A systematic approach (framework) developed to aid in the selection of the most suitable commercial-scale magnet designs is presented and the program status as of September 1982 is reported. Recommendations are made for future work needed to complete the design evaluation and selection process and to provide a sound technological base for the detail design and construction of commercial-scale MHD magnets. 85 references.

  5. Parametric analysis of closed cycle magnetohydrodynamic (MHD) power plants

    NASA Technical Reports Server (NTRS)

    Owens, W.; Berg, R.; Murthy, R.; Patten, J.

    1981-01-01

    A parametric analysis of closed cycle MHD power plants was performed which studied the technical feasibility, associated capital cost, and cost of electricity for the direct combustion of coal or coal derived fuel. Three reference plants, differing primarily in the method of coal conversion utilized, were defined. Reference Plant 1 used direct coal fired combustion while Reference Plants 2 and 3 employed on site integrated gasifiers. Reference Plant 2 used a pressurized gasifier while Reference Plant 3 used a ""state of the art' atmospheric gasifier. Thirty plant configurations were considered by using parametric variations from the Reference Plants. Parametric variations include the type of coal (Montana Rosebud or Illinois No. 6), clean up systems (hot or cold gas clean up), on or two stage atmospheric or pressurized direct fired coal combustors, and six different gasifier systems. Plant sizes ranged from 100 to 1000 MWe. Overall plant performance was calculated using two methodologies. In one task, the channel performance was assumed and the MHD topping cycle efficiencies were based on the assumed values. A second task involved rigorous calculations of channel performance (enthalpy extraction, isentropic efficiency and generator output) that verified the original (task one) assumptions. Closed cycle MHD capital costs were estimated for the task one plants; task two cost estimates were made for the channel and magnet only.

  6. Reconstruction of Plasma Equilibria and Projected Stabilization of Global MHD Modes in KSTAR

    NASA Astrophysics Data System (ADS)

    Park, Y. S.; Sabbagh, S. A.; Bialek, J. M.; Berkery, J. W.; Jeon, Y. M.; Hahn, S. H.; Lee, S. G.; You, K.-. I.; Park, H. K.; Evans, T. E.; Eidietis, N.; Walker, M.; Leuer, J.

    2010-11-01

    Experimental equilibria of the KSTAR tokamak with plasma current up to 0.34 MA were reconstructed using EFIT. Vessel currents were included by fitting estimated values based on loop voltage measurements and effective resistances from 2 and 3-D vacuum model calculations including a double-walled vessel with large port penetrations and passive stabilizers. Active and passive stabilization of global MHD instabilities for operation above the no-wall beta limit is also projected. The stabilization is applied using a set of segmented internal coils called in-vessel control coils (IVCCs). Passive stability of the resistive wall mode and power requirement for its active stabilization are investigated including conductive casing structures covering the IVCC, and noise effects. The potential for ELM mitigation by resonant magnetic perturbations is also examined by using the TRIP3D code. Favorable configurations of the IVCC based on the Chirikov parameter are determined using a combination of all IVCCs (midplane and off-midplane coils) with a dominant n = 2 field configuration.

  7. 17th Workshop on MHD Stability Control: addressing the disruption challenge for ITER

    NASA Astrophysics Data System (ADS)

    Buttery, Richard

    2013-08-01

    This annual workshop on magnetohydrodynamic stability control was held on 5-7 November 2012 at Columbia University in the city of New York, in the aftermath of a violent hydrodynamic instability event termed 'Hurricane Sandy'. Despite these challenging circumstances, Columbia University managed an excellent meeting, enabling the full participation of the community. This Workshop has been held since 1996 to help in the development of understanding and control of magnetohydrodynamic (MHD) instabilities for future fusion reactors. It covers a wide range of stability topics—from disruptions, to tearing modes, error fields, edge-localized modes (ELMs), resistive wall modes (RWMs) and ideal MHD—spanning many device types (tokamaks, stellarators and reversed field pinches) to identify commonalities in the physics and a means of control. The theme for 2012 was 'addressing the disruption challenge for ITER', and thus the first day had a heavy focus on both the avoidance and mitigation of disruptions in ITER. Key elements included understanding how to apply 3D fields to maintain stability, as well as managing the disruption process itself through mitigating loads in the thermal quench and handling so called 'runaway electrons'. This culminated in a panel discussion on the disruption mitigation strategy for ITER, which noted that heat load asymmetries during the thermal quench appear to be an artifact of MHD processes, and that runaway electron generation may be inevitable, suggesting research should focus on control and dissipation of the runaway beam. The workshop was combined this year with the annual US-Japan MHD Workshop, with a special section looking more deeply at 'Fundamentals of 3D Perturbed Equilibrium Control', with interesting sessions on 3D equilibrium reconstruction, RWM physics, novel control concepts such as non-magnetic sensing, adaptive control, q < 2 tokamak operation, and the effects of flow. The final day turned to tearing mode interactions

  8. MHD equilibria with diamagnetic effects

    NASA Astrophysics Data System (ADS)

    Tessarotto, M.; Zorat, R.; Johnson, J. L.; White, R. B.

    1997-11-01

    An outstanding issue in magnetic confinement is the establishment of MHD equilibria with enhanced flow shear profiles for which turbulence (and transport) may be locally effectively suppressed or at least substantially reduced with respect to standard weak turbulence models. Strong flows develop in the presence of equilibrium E× B-drifts produced by a strong radial electric field, as well as due to diamagnetic contributions produced by steep equilibrium radial profiles of number density, temperature and the flow velocity itself. In the framework of a kinetic description, this generally requires the construction of guiding-center variables correct to second order in the relevant expansion parameter. For this purpose, the Lagrangian approach developed recently by Tessarotto et al. [1] is adopted. In this paper the conditions of existence of such equilibria are analyzed and their basic physical properties are investigated in detail. 1 - M. Pozzo, M. Tessarotto and R. Zorat, in Theory of fusion Plasmas, E.Sindoni et al. eds. (Societá Italiana di Fisica, Editrice Compositori, Bologna, 1996), p.295.

  9. MHD Integrated Topping Cycle Project

    SciTech Connect

    Not Available

    1992-02-01

    This fourteenth quarterly technical progress report of the MHD Integrated Topping Cycle Project presents the accomplishments during the period November 1, 1990 to January 31, 1991. Testing of the High Pressure Cooling Subsystem electrical isolator was completed. The PEEK material successfully passed the high temperature, high pressure duration tests (50 hours). The Combustion Subsystem drawings were CADAM released. The procurement process is in progress. An equipment specification and RFP were prepared for the new Low Pressure Cooling System (LPCS) and released for quotation. Work has been conducted on confirmation tests leading to final gas-side designs and studies to assist in channel fabrication.The final cathode gas-side design and the proposed gas-side designs of the anode and sidewall are presented. Anode confirmation tests and related analyses of anode wear mechanisms used in the selection of the proposed anode design are presented. Sidewall confirmation tests, which were used to select the proposed gas-side design, were conducted. The design for the full scale CDIF system was completed. A test program was initiated to investigate the practicality of using Avco current controls for current consolidation in the power takeoff (PTO) regions and to determine the cause of past current consolidation failures. Another important activity was the installation of 1A4-style coupons in the 1A1 channel. A description of the coupons and their location with 1A1 channel is presented herein.

  10. MHD waveguides in space plasma

    SciTech Connect

    Mazur, N. G.; Fedorov, E. N.; Pilipenko, V. A.

    2010-07-15

    The waveguide properties of two characteristic formations in the Earth's magnetotail-the plasma sheet and the current (neutral) sheet-are considered. The question of how the domains of existence of different types of MHD waveguide modes (fast and slow, body and surface) in the (k, {omega}) plane and their dispersion properties depend on the waveguide parameters is studied. Investigation of the dispersion relation in a number of particular (limiting) cases makes it possible to obtain a fairly complete qualitative pattern of all the branches of the dispersion curve. Accounting for the finite size of perturbations across the wave propagation direction reveals new additional effects such as a change in the critical waveguide frequencies, the excitation of longitudinal current at the boundaries of the sheets, and a change in the symmetry of the fundamental mode. Knowledge of the waveguide properties of the plasma and current sheets can explain the occurrence of preferred frequencies in the low-frequency fluctuation spectra in the magnetotail. In satellite observations, the type of waveguide mode can be determined from the spectral properties, as well as from the phase relationships between plasma oscillations and magnetic field oscillations that are presented in this paper.

  11. Performance of Combustion Disk MHD Generators.

    NASA Astrophysics Data System (ADS)

    Jenkins, Marion Karl

    of Hall fields were investigated using external voltage augmentation, and electric fields of 9 KV/m were observed in the channel with no evidence of breakdown. The analytical work consisted of the development of a two-dimensional computer program to predict boundary layer phenomena in disk generators, including the effects of turbulence, variable gas properties and MHD interaction. The numerical results show the effect of the variable MHD body force across the insulating wall boundary layer, giving rise to boundary layer velocities higher than those in the core. This leads to greater skin friction and heat transfer losses than what would be predicted with a quasi -one dimensional model. Calculations carried out for baseload -sized generators show the expected dependence of boundary layer behavior on channel operating conditions such as wall temperature, swirl, magnetic field strength and channel loading.

  12. The Effect of Ivermectin in Seven Strains of Aedes aegypti (Diptera: Culicidae) Including a Genetically Diverse Laboratory Strain and Three Permethrin Resistant Strains

    PubMed Central

    Deus, K. M.; Saavedra-rodriguez, K.; Butters, M. P.; Black, W. C.; Foy, B. D.

    2014-01-01

    Seven different strains of Aedes aegypti (L.), including a genetically diverse laboratory strain, three laboratory-selected permethrin-resistant strains, a standard reference strain, and two recently colonized strains were fed on human blood containing various concentrations of ivermectin. Ivermectin reduced adult survival, fecundity, and hatch rate of eggs laid by ivermectin-treated adults in all seven strains. The LC50 of ivermectin for adults and the concentration that prevented 50% of eggs from hatching was calculated for all strains. Considerable variation in adult survival after an ivermectin-bloodmeal occurred among strains, and all three permethrin-resistant strains were significantly less susceptible to ivermectin than the standard reference strain. The hatch rate after an ivermectin bloodmeal was less variable among strains, and only one of the permethrin-resistant strains differed significantly from the standard reference strain. Our studies suggest that ivermectin induces adult mortality and decreases the hatch rate of eggs through different mechanisms. A correlation analysis of log-transformed LC50 among strains suggests that permethrin and ivermectin cross-resistance may occur. PMID:22493855

  13. Edge biasing effects on MHD instabilities and plasma response to external magnetic perturbations in HBT-EP

    NASA Astrophysics Data System (ADS)

    Debono, Bryan; Maurer, Dave; Mauel, Michael; L., Jeff; Daisuke, S.; Niko, R.; Navratil, Gerald; A., Sarah; B., Pat; Pedersen, Thomas; HBT-EP Team

    2011-10-01

    A biased electrode inserted into a tokamak plasma edge can be used to apply torque on the plasma and change the rotation rate of MHD instabilities, including the resistive wall mode (RWM). RWM's in HBT-EP have a natural frequency of +4-9 kHz, however with appropriate bias the plasma rotation can be adjusted both positively and negatively. We present a study of the effect of biased plasma rotation on MHD instabilities; a comparison is made between plasma rotation rate and the plasma response to external resonant magnetic perturbations (RMP). The Boozer tokamak plasma reluctance equation ρ = -(1/s - iα + 1) 1/Lp suggests that the plasma response to RMP's is greatly enhanced as the toroidal torque dissapation coefficient α --> 0 . Moderate biasing (~ 50V) slows down the RWM rotation to 2-3kHz, and an increase in the plasma responsivity to RMP's is seen. Strong positive bias (~ + 300 V) accelerates the mode in the direction opposite to its natural rotation at ~ -40 kHz. At this high rotation frequency the mode is being dragged at too rapid a rate for it to penetrate the wall. Therefore, the conducting shells behave like an ideal wall and a saturated ideal external kink is observed instead of a RWM.

  14. "Ideal" tearing and the transition to fast reconnection in the weakly collisional MHD and EMHD regimes

    NASA Astrophysics Data System (ADS)

    Del Sarto, Daniele; Pucci, Fulvia; Tenerani, Anna; Velli, Marco

    2016-03-01

    This paper discusses the transition to fast growth of the tearing instability in thin current sheets in the collisionless limit where electron inertia drives the reconnection process. It has been previously suggested that in resistive MHD there is a natural maximum aspect ratio (ratio of sheet length and breadth to thickness) which may be reached for current sheets with a macroscopic length L, the limit being provided by the fact that the tearing mode growth time becomes of the same order as the Alfvén time calculated on the macroscopic scale. For current sheets with a smaller aspect ratio than critical the normalized growth rate tends to zero with increasing Lundquist number S, while for current sheets with an aspect ratio greater than critical the growth rate diverges with S. Here we carry out a similar analysis but with electron inertia as the term violating magnetic flux conservation: previously found scalings of critical current sheet aspect ratios with the Lundquist number are generalized to include the dependence on the ratio de2/L2, where de is the electron skin depth, and it is shown that there are limiting scalings which, as in the resistive case, result in reconnecting modes growing on ideal time scales. Finite Larmor radius effects are then included, and the rescaling argument at the basis of "ideal" reconnection is proposed to explain secondary fast reconnection regimes naturally appearing in numerical simulations of current sheet evolution.

  15. Modeling of substorm development with a kinematic effect by the global MHD simulations

    NASA Astrophysics Data System (ADS)

    den, Mitsue; Fujita, Shigeru; Tanaka, Takashi; Horiuchi, Ritoku

    Magnetic reconnection is considered to play an important role in space phenomena such as substorm in the Earth's magnetosphere. Recently, Tanaka and Fujita reproduced substorm evoution process by numerical simulation with the global MHD code. In the MHD framework, the dissipation model is used for modeling of the kinetic effects. They found that the normalized reconnection viscosity, one of the dessipation model employed there, gave a large effect for the substorm development though that viscosity was assumed to be a constant parameter. It is well known that magnetric reconnection is controlled by microscopic kinetic mechanism. Horiuchi et al. investigated the roles of microscopic plasma instabilities on the violation of the frozen-in condition by examining the force balance equation based on explicit electromagnetic particle simulation for an ion-scale current sheet, and concluded that the growth of drift kink instability can create anomalous resistivity leading to the excitation of collisionless reconnection. They estimated the effective resistivity based on the particle simulation data. In this paper, we perform substorm simulation by using the global MHD code with this anomalous resistivity obtained in their microscopic approach istead of the emprical resistivity model, and investigate the relationship between the substorm development and the anomalous resistivity model.

  16. Efficacy of interventions that include diet, aerobic and resistance training components for type 2 diabetes prevention: a systematic review with meta-analysis.

    PubMed

    Aguiar, Elroy J; Morgan, Philip J; Collins, Clare E; Plotnikoff, Ronald C; Callister, Robin

    2014-01-15

    Current recommendations for the prevention of type 2 diabetes advise modification of diet and exercise behaviors including both aerobic and resistance training. However, the efficacy of multi-component interventions involving a combination of these three components has not been established. The aims of this review were to systematically review and meta-analyze the evidence on multi-component (diet + aerobic exercise + resistance training) lifestyle interventions for type 2 diabetes prevention. Eight electronic databases (Medline, Embase, SportDiscus, Web of Science, CINAHL, Informit health collection, Cochrane library and Scopus) were searched up to June 2013. Eligible studies 1) recruited prediabetic adults or individuals at risk of type 2 diabetes; 2) conducted diet and exercise [including both physical activity/aerobic and resistance training] programs; and 3) reported weight and plasma glucose outcomes. In total, 23 articles from eight studies were eligible including five randomized controlled trials, one quasi-experimental, one two-group comparison and one single-group pre-post study. Four studies had a low risk of bias (score ≥ 6/10). Median intervention length was 12 months (range 4-48 months) with a follow-up of 18 months (range 6.5-48 months). The diet and exercise interventions varied slightly in terms of their specific prescriptions. Meta-analysis favored interventions over controls for weight loss (-3.79 kg [-6.13, -1.46; 95% CI], Z = 3.19, P = 0.001) and fasting plasma glucose (-0.13 mmol.L⁻¹ [-0.24, -0.02; 95% CI], Z = 2.42, P = 0.02). Diabetes incidence was only reported in two studies, with reductions of 58% and 56% versus control groups. In summary, multi-component lifestyle type 2 diabetes prevention interventions that include diet and both aerobic and resistance exercise training are modestly effective in inducing weight loss and improving impaired fasting glucose, glucose tolerance, dietary and exercise outcomes

  17. Efficacy of interventions that include diet, aerobic and resistance training components for type 2 diabetes prevention: a systematic review with meta-analysis

    PubMed Central

    2014-01-01

    Current recommendations for the prevention of type 2 diabetes advise modification of diet and exercise behaviors including both aerobic and resistance training. However, the efficacy of multi-component interventions involving a combination of these three components has not been established. The aims of this review were to systematically review and meta-analyze the evidence on multi-component (diet + aerobic exercise + resistance training) lifestyle interventions for type 2 diabetes prevention. Eight electronic databases (Medline, Embase, SportDiscus, Web of Science, CINAHL, Informit health collection, Cochrane library and Scopus) were searched up to June 2013. Eligible studies 1) recruited prediabetic adults or individuals at risk of type 2 diabetes; 2) conducted diet and exercise [including both physical activity/aerobic and resistance training] programs; and 3) reported weight and plasma glucose outcomes. In total, 23 articles from eight studies were eligible including five randomized controlled trials, one quasi-experimental, one two-group comparison and one single-group pre-post study. Four studies had a low risk of bias (score ≥ 6/10). Median intervention length was 12 months (range 4–48 months) with a follow-up of 18 months (range 6.5 - 48 months). The diet and exercise interventions varied slightly in terms of their specific prescriptions. Meta-analysis favored interventions over controls for weight loss (-3.79 kg [-6.13, -1.46; 95% CI], Z = 3.19, P = 0.001) and fasting plasma glucose (-0.13 mmol.L-1 [-0.24, -0.02; 95% CI], Z = 2.42, P = 0.02). Diabetes incidence was only reported in two studies, with reductions of 58% and 56% versus control groups. In summary, multi-component lifestyle type 2 diabetes prevention interventions that include diet and both aerobic and resistance exercise training are modestly effective in inducing weight loss and improving impaired fasting glucose, glucose tolerance, dietary and exercise

  18. Tigecycline Nonsusceptibility Occurs Exclusively in Fluoroquinolone-Resistant Escherichia coli Clinical Isolates, Including the Major Multidrug-Resistant Lineages O25b:H4-ST131-H30R and O1-ST648.

    PubMed

    Sato, Toyotaka; Suzuki, Yuuki; Shiraishi, Tsukasa; Honda, Hiroyuki; Shinagawa, Masaaki; Yamamoto, Soh; Ogasawara, Noriko; Takahashi, Hiroki; Takahashi, Satoshi; Tamura, Yutaka; Yokota, Shin-Ichi

    2017-02-01

    Tigecycline (TGC) is a last-line drug for multidrug-resistant Enterobacteriaceae We investigated the mechanism(s) underlying TGC nonsusceptibility (TGC resistant/intermediate) in Escherichia coli clinical isolates. The MIC of TGC was determined for 277 fluoroquinolone-susceptible isolates (ciprofloxacin [CIP] MIC, <0.125 mg/liter) and 194 fluoroquinolone-resistant isolates (CIP MIC, >2 mg/liter). The MIC50 and MIC90 for TGC in fluoroquinolone-resistant isolates were 2-fold higher than those in fluoroquinolone-susceptible isolates (MIC50, 0.5 mg/liter versus 0.25 mg/liter; MIC90, 1 mg/liter versus 0.5 mg/liter, respectively). Two fluoroquinolone-resistant isolates (O25b:H4-ST131-H30R and O125:H37-ST48) were TGC resistant (MICs of 4 and 16 mg/liter, respectively), and four other isolates of O25b:H4-ST131-H30R and an isolate of O1-ST648 showed an intermediate interpretation (MIC, 2 mg/liter). No TGC-resistant/intermediate strains were found among the fluoroquinolone-susceptible isolates. The TGC-resistant/intermediate isolates expressed higher levels of acrA and acrB and had lower intracellular TGC concentrations than susceptible isolates, and they possessed mutations in acrR and/or marR The MICs of acrAB-deficient mutants were markedly lower (0.25 mg/liter) than those of the parental strain. After continuous stepwise exposure to CIP in vitro, six of eight TGC-susceptible isolates had reduced TGC susceptibility. Two of them acquired TGC resistance (TGC MIC, 4 mg/liter) and exhibited expression of acrA and acrB and mutations in acrR and/or marR In conclusion, a population of fluoroquinolone-resistant E. coli isolates, including major extraintestinal pathogenic lineages O25b:H4-ST131-H30R and O1-ST648, showed reduced susceptibility to TGC due to overexpression of the efflux pump AcrAB-TolC, leading to decreased intracellular concentrations of the antibiotics that may be associated with the development of fluoroquinolone resistance.

  19. Dipole Alignment in Rotating MHD Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.; Fu, Terry; Morin, Lee

    2012-01-01

    We present numerical results from long-term CPU and GPU simulations of rotating, homogeneous, magnetohydrodynamic (MHD) turbulence, and discuss their connection to the spherically bounded case. We compare our numerical results with a statistical theory of geodynamo action that has evolved from the absolute equilibrium ensemble theory of ideal MHD turbulence, which is based on the ideal MHD invariants are energy, cross helicity and magnetic helicity. However, for rotating MHD turbulence, the cross helicity is no longer an exact invariant, although rms cross helicity becomes quasistationary during an ideal MHD simulation. This and the anisotropy imposed by rotation suggests an ansatz in which an effective, nonzero value of cross helicity is assigned to axisymmetric modes and zero cross helicity to non-axisymmetric modes. This hybrid statistics predicts a large-scale quasistationary magnetic field due to broken ergodicity , as well as dipole vector alignment with the rotation axis, both of which are observed numerically. We find that only a relatively small value of effective cross helicity leads to the prediction of a dipole moment vector that is closely aligned (less than 10 degrees) with the rotation axis. We also discuss the effect of initial conditions, dissipation and grid size on the numerical simulations and statistical theory.

  20. Prevalence and Characterization of Staphylococcus aureus, Including Methicillin-Resistant Staphylococcus aureus, Isolated from Bulk Tank Milk from Minnesota Dairy Farms

    PubMed Central

    Haran, K. P.; Godden, S. M.; Boxrud, D.; Jawahir, S.; Bender, J. B.

    2012-01-01

    Staphylococcus aureus is a common causative agent of bovine mastitis in dairy herds. The emergence of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals as well as the community is a significant and costly public health concern. S. aureus-related bovine mastitis is a common reason for therapeutic and/or prophylactic use of antibiotics on dairy farms. In this study, herd prevalence of S. aureus, including MRSA, was estimated from bulk tank milk (BTM) from Minnesota farms. A total of 150 pooled BTM samples from 50 farms, collected over 3 seasons (spring, summer, and fall of 2009), were assessed. Herd prevalence of methicillin-susceptible S. aureus (MSSA) was 84%, while MRSA herd prevalence was 4%. A total of 93 MSSA isolates and 2 MRSA isolates were recovered from 150 BTM samples. Antibiotic susceptibility testing of S. aureus isolates showed pansusceptibility in 54 isolates, resistance to a single antibiotic class in 21 isolates, resistance to two antibiotic classes in 13 isolates, and resistance to ≥3 antibiotics classes and thus multidrug resistance in 5 isolates. The two MRSA isolates displayed resistance to β-lactams, cephalosporins, and lincosamides and were multiresistant. Staphylococcal protein A gene (spa) typing identified spa types t529 and t034 most frequently among methicillin-susceptible isolates, while t121 was observed in MRSA isolates. Seven isolates, including the two MRSA isolates, produced staphylococcal enterotoxins B, C, D, and E on overnight culture. MRSA isolates were further genotyped using multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). Of the 2 MRSA isolates, one had a composite genotype profile of MLST ST 5-PFGE USA100-unknown spa type, which has been reported among hospital-associated MRSA isolates, while the second isolate carried the MLST ST 8-PFGE USA300-spa type t121 genotype, commonly identified among community-associated MRSA isolates. These results suggest that MRSA genotypes

  1. MHD simulations of supernova driven ISM turbulence

    NASA Astrophysics Data System (ADS)

    Gressel, Oliver; Ziegler, Udo

    The dynamic evolution of the (stratified) turbulent interstellar medium (ISM) is simulated utilizing a three-dimensional MHD model including various physical effects. The computational domain covers a box of 0.5x0.5x2.0 kpc at a resolution of typically 128x128x1024 grid cells. The model includes (constant kinematic) viscosity and magnetic diffusivity. The adiabatic equation of state is supplemented by a parameterized heating- and cooling-function allowing for thermal instability (TI). The update due to heating and cooling is implemented implicitly using a Patankar-type discretization. Turbulence is driven by supernova explosions which are modelled as local injections of thermal energy, smeared over three standard-deviations of a Gaussian support with FWHM of 20pc. Supernova rates are adopted for typical cited values. Within our model we make a distinction between Type I and Type II SNe. Latter are statistically clustered by the (artificial) constraint that the density at the explosion site be above average (with respect to a horizontal slab) - former are spatially uncorrelated. The dual-energy feature of the conservative NIRVANA-code is used to tackle the extreme ratio of kinetic to internal energy that arises from the violent energy input. We stress the importance of using a conservative scheme to properly transfer the injected energy to kinetic motion. The model also includes a differentially rotating background (with shearing boundary conditions in radial direction) as well as vertical stratification. The initial density and pressure profiles are in hydrostatic equilibrium with respect to the equation of state given by the radiative equilibrium. Including z-dependent heating rates this leads to a considerable deviation from usual isothermal initial models. The primary focus of this work is on the galactic dynamo and the generation of large-scale magnetic fields. As a secondary target we are also interested in general properties of the ISM that are of importance

  2. Slow shock and rotational discontinuity in MHD and Hall MHD models with anisotropic pressure

    NASA Astrophysics Data System (ADS)

    Hau, L.-N.; Wang, B.-J.

    2016-07-01

    Pressure anisotropy may modify the characteristics of magnetohydrodynamic (MHD) waves, in particular, the slow mode wave and the corresponding shocks and discontinuities. In this study the formation of slow shocks (SSs) in anisotropic plasmas is examined by solving the gyrotropic MHD and Hall MHD equations numerically for one-dimensional Riemann problem. The MHD shocks and discontinuities are generated by imposing a finite normal magnetic field on the Harris type current sheet with a guide magnetic By component. It is shown that anomalous SSs moving faster than the intermediate wave or with positive density-magnetic field correlation may be generated in gyrotropic MHD and Hall MHD models. Moreover, for some parameter values SSs may exhibit upstream wave trains with right-handed polarization in contrast with the earlier prediction that SSs shall possess downstream left-hand polarized wave trains based on the isotropic Hall MHD theory. For the cases of By ≠ 0, SSs with increased density and decreased magnetic field followed by noncoplanar intermediate mode or rotational discontinuity (RD)-like structures similar to the compound SS-RD structures observed in space plasma environments may possibly form in symmetric and asymmetric current layers. The Walén relation of these anomalous RDs without the correction of pressure anisotropy may significantly be violated.

  3. MHD Modeling of the Transition Region Using Realistic Transport Coefficients

    NASA Astrophysics Data System (ADS)

    Goodman, Michael L.

    1997-05-01

    Most of the transition region (TR) consists of a collision dominated plasma. The dissipation and transport of energy in such a plasma is accurately described by the well known classical transport coefficients which include the electrical and thermal conductivity, viscosity, and thermo- electric tensors. These tensors are anisotropic and are functions of local values of temperature, density, and magnetic field. They may be used in an MHD model to obtain a self consistent, physically realistic description of the TR. The physics of kinetic processes is included in the MHD model through the transport coefficients. As a first step in studying heating and cooling processes in the TR in a realistic, quantitative manner, a 1.5 dimensional, steady state MHD model with a specified temperature profile is considered. The momentum equation includes the inertial, pressure gradient, Lorentz, and gravitational forces. The Ohm's law includes the exact expressions for the electrical conductivity and thermo- electric tensors. The electrical conductivity relates the generalized electric field to the conduction current density while the thermo-electric tensor relates the temperature gradient to the thermo-electric current density. The total current density is the sum of the two. It is found that the thermo-electric current density can be as large as the conduction current density, indicating that thermo-electric effects are probably important in modeling the dynamics of energy dissipation, such as wave dissipation, in the TR. Although the temperature gradient is in the vertical direction, the thermo-electric current density is in the horizontal direction, indicating the importance of the effects of anisotropic transport. The transport coefficients are valid for all magnetic field strengths, and so may be used to study the physics of weakly as well as strongly magnetized regions of the TR. Numerical examples are presented.

  4. MHD energy fluxes for late type dwarfs

    NASA Technical Reports Server (NTRS)

    Rosner, R.; Musielak, Z. E.

    1987-01-01

    The efficiency of MHD wave generation by turbulent motions in stratified stellar atmospheres with embedded uniform magnetic fields is calculated. In contradiction with previous results, it is shown that there is no significant increase in the efficiency of wave generation because of the presence of magnetic fields, at least within the theory's limits of applicability. It is shown that MHD energy fluxes for late-type stars are less than those obtained for acoustic waves in a magnetic-field-free atmosphere, and do not vary enough for a given spectral type in order to explain observed UV and X-ray fluxes. Thus, the results show that MHD energy fluxes obtained if stellar surface magnetic fields are uniform cannot explain the observed stellar coronal emissions.

  5. Simulation of wave interactions with MHD

    SciTech Connect

    Batchelor, Donald B; Abla, G; Bateman, Glenn; Bernholdt, David E; Berry, Lee A; Bonoli, P.; Bramley, R; Breslau, J.; Chance, M.; Chen, J.; Choi, M.; Elwasif, Wael R; Fu, GuoYong; Harvey, R. W.; Jaeger, Erwin Frederick; Jardin, S. C.; Jenkins, T; Keyes, David E; Klasky, Scott A; Kruger, Scott; Ku, Long-Poe; Lynch, Vickie E; McCune, Douglas; Ramos, J.; Schissel, D.; Schnack,; Wright, J.

    2008-07-01

    The broad scientific objectives of the SWIM (Simulation of Wave Interaction with MHD) project are twofold: (1) improve our understanding of interactions that both radio frequency (RF) wave and particle sources have on extended-MHD phenomena, and to substantially improve our capability for predicting and optimizing the performance of burning plasmas in devices such as ITER: and (2) develop an integrated computational system for treating multiphysics phenomena with the required flexibility and extensibility to serve as a prototype for the Fusion Simulation Project. The Integrated Plasma Simulator (IPS) has been implemented. Presented here are initial physics results on RF effects on MHD instabilities in tokamaks as well as simulation results for tokamak discharge evolution using the IPS.

  6. MHD modeling of dense plasma focus electrode shape variation

    NASA Astrophysics Data System (ADS)

    McLean, Harry; Hartman, Charles; Schmidt, Andrea; Tang, Vincent; Link, Anthony; Ellsworth, Jen; Reisman, David

    2013-10-01

    The dense plasma focus (DPF) is a very simple device physically, but results to date indicate that very extensive physics is needed to understand the details of operation, especially during the final pinch where kinetic effects become very important. Nevertheless, the overall effects of electrode geometry, electrode size, and drive circuit parameters can be informed efficiently using MHD fluid codes, especially in the run-down phase before the final pinch. These kinds of results can then guide subsequent, more detailed fully kinetic modeling efforts. We report on resistive 2-d MHD modeling results applying the TRAC-II code to the DPF with an emphasis on varying anode and cathode shape. Drive circuit variations are handled in the code using a self-consistent circuit model for the external capacitor bank since the device impedance is strongly coupled to the internal plasma physics. Electrode shape is characterized by the ratio of inner diameter to outer diameter, length to diameter, and various parameterizations for tapering. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  7. High-. beta. operation and MHD (magnetohydrodynamic) activity on TFTR

    SciTech Connect

    McGuire, K.

    1990-04-01

    Magnetohydrodynamic (MHD) activity within three zones (core, half- radius, and edge) of TFTR (Plasma Physics and Controlled Nuclear Fusion Research (1986), (IAEA, Vienna, 1987), Vol. 1, P. 51) tokamak plasmas are discussed. Near the core of the plasma column, sawteeth are often observed. Two types of sawteeth are studied in detail: one with complete, and the other with incomplete magnetic reconnection. Their characteristics are determined by the shape of the q profile. Near the half-radius the m/n = 3/2 and 2/1 resistive ballooning modes are found to correlate with a beta collapse. The pressure and the pressure gradient at the mode rational surface are found to play an important role in stability. MHD activity is also studied at the plasma edge during limiter H-modes. The Edge Localized Mode (ELMs) are found to have a precursor mode with a frequency between 50--200 kHz and a mode number m/n = 1/0. The mode does not show a ballooning structure. While these instabilities have been studied on many other machines, on TFTR the studies have been extended to high pressure (plasma pressure greater than 4 {times} 10{sup 5} Pa) and low collisionality. 16 refs., 3 figs.

  8. MHD dynamo and charge separation for the Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Cappello, Susanna; Bonfiglio, Daniele; Franck Escande, Dominique

    2004-11-01

    The reversed field pinch (RFP) is a toroidal configuration for magnetic confinement characterized by a plasma current strong enough to excite a kink instability. Though according to the standard paradigm developed in the 80'-90' the ensuing MHD turbulence would be intrinsic to the RFP dynamo, more recent studies go beyond this view. Three-dimensional visco-resistive MHD simulations display a transition from multiple helicity (MH) states to single helicity (SH) steady states [1] when dissipation is increased. These SH states provide a laminar dynamo for the RFP. The present work unveils the features of these SH states by performing a detailed analysis of numerical simulations. Since this state is stationary, the electric field is curl-free. Poisson equation reveals a charge separation, which is small enough to be consistent with the quasi-neutrality condition. This charge separation is shown to play a key role in the dynamo effect, since the related electrostatic field produces a drift velocity which is the main part of the dynamo velocity field. This physical interpretation of the dynamo, involving a leading role of the charge separation, can be extended to the quasi single helicity (QSH) states found in RFP devices as well as to turbulent MH states. [1] S. Cappello and D.F. Escande , Physical Review Letters 85-18 (2000) 3838

  9. Neon Induced MHD Activity in FTU

    NASA Astrophysics Data System (ADS)

    Botrugno, A.; Buratti, P.; Marinucci, M.; Mazzotta, C.; Pucella, G.; Romano, A.; Sozzi, C.

    The m/n=2/1 tearing instability driven by rapid increasing of the current density gradient near the q=2 radius induced by Ne puffing has discussed for different Frascati Tokamak Upgraded (FTU) L-mode ohmic plasmas. The dynamic of modes can be divided in three phases. The formation and dynamic of MHD activity strictly depends on the amount of Ne in plasma, for this reason, Ne puffing represents a very efficient method to deliberately induce formation of repeatable MHD targets for different experimental needs.

  10. Modeling of Feedback Stabilization of External MHD Modes in Toroidal Geometry

    NASA Astrophysics Data System (ADS)

    Chu, M. S.; Chance, M. S.; Okabayashi, M.

    2000-10-01

    The intelligent shell feedback scheme(C.M. Bishop, Plasma Phys. Contr. Nucl. Fusion 31), 1179 (1989). seeks to utilize external coils to suppress the unstable MHD modes slowed down by the resistive shell. We present a new formulation and numerical results of the interaction between the plasma and its outside vacuum region, with complete plasma response and the inclusion of a resistive vessel in general toroidal geometry. This is achieved by using the Green's function technique, which is a generalization of that previously used for the VACUUM(M.S. Chance, Phys. Plasmas 4), 2161 (1997). code and coupled with the ideal MHD code GATO. The effectiveness of different realizations of the intelligent shell concept is gauged by their ability to minimize the available free energy to drive the MHD mode. Computations indicate poloidal coverage of 30% of the total resistive wall surface area and 6 or 7 segments of ``intelligent coil'' arrays superimposed on the resistive wall will allow recovery of up to 90% the effectiveness of the ideal shell in stabilizing the ideal external kink.

  11. Smoothed MHD equations for numerical simulations of ideal quasi-neutral gas dynamic flows

    NASA Astrophysics Data System (ADS)

    Popov, Mikhail V.; Elizarova, Tatiana G.

    2015-11-01

    We introduce a mathematical model and related numerical method for numerical modeling of ideal magnetohydrodynamic (MHD) gas flows as an extension of previously known quasi-gasdynamic (QGD) equations. This approach is based on smoothing, or averaging of the original MHD equation system over a small time interval that leads to a new equation system, named quasi-MHD, or QMHD system. The QMHD equations are closely related to the original MHD system except for additional strongly non-linear dissipative τ-terms with a small parameter τ as a factor. The τ-terms depend on the solution itself and decrease in regions with the small space gradients of the solution. In this sense the QMHD system could be regarded as an approach with adaptive artificial dissipation. The QMHD is a generalization of regularized (or quasi-) gas dynamic equation system suggested in last three decades. In the QMHD numerical method the evolution of all physical variables is presented in a non-split divergence form. Divergence-free evolution of the magnetic field provides by using a constrained transport method based on Faraday's law of induction. Accuracy and convergence of the QMHD method is verified on a wide set of standard MHD tests including the 3D Orszag-Tang vortex flow.

  12. MHD and Kinetic Modeling of the Ionospheres of Venus and Mars

    SciTech Connect

    Shinagawa, H.; Terada, N.

    2009-06-16

    It is widely recognized that both Venus and Mars possess no significant global intrinsic magnetic fields, and that the solar wind interacts directly with the upper atmospheres and ionospheres of Venus and Mars. In addition, local crustal magnetic fields are also present in various regions at Mars, suggesting that some regions of the Martian ionosphere are influenced not only by the solar wind but also by the crustal magnetic field. Previous studies have suggested that the basic structures of the ionospheres of the planets can be described by fluid and MHD(magnetohydrodynamic) processes. Various models of the ionospheres of Venus and Mars based on the MHD formulation have been constructed during the last two decades. Although the MHD approach has been successful in reproducing the ionospheres of the planets, some studies have indicated that MHD modeling is not necessarily appropriate in the regions of the topside ionosphere, the ionopause, and the magnetosheath, where the ion kinetic processes are likely to play an important role. The kinetic processes in the topside ionosphere might have significant influences even in the lower ionosphere. Thanks to a great progress made for computer power as well as the efficiency of calculations of the hybrid model, high-resolution kinetic models of the solar wind interaction with Venus and Mars, which self-consistently include the ionosphere, have been developed. In this paper, status of MHD and kinetic modeling of the ionospheres of Venus and Mars is briefly reviewed.

  13. Decreasing population selection rates of resistance mutation K65R over time in HIV-1 patients receiving combination therapy including tenofovir

    PubMed Central

    Theys, K.; Snoeck, J.; Vercauteren, J.; Abecasis, A. B.; Vandamme, A.-M.; Camacho, R. J.

    2013-01-01

    Objectives The use of tenofovir is highly associated with the emergence of mutation K65R, which confers broad resistance to nucleoside/nucleotide analogue reverse transcriptase inhibitors (NRTIs), especially when tenofovir is combined with other NRTIs also selecting for K65R. Although recent HIV-1 treatment guidelines discouraging these combinations resulted in reduced K65R selection with tenofovir, updated information on the impact of currently recommended regimens on the population selection rate of K65R is presently lacking. Methods In this study, we evaluated changes over time in the selection rate of resistance mutation K65R in a large population of 2736 HIV-1-infected patients failing combination antiretroviral treatment between 2002 and 2010. Results The K65R resistance mutation was detected in 144 patients, a prevalence of 5.3%. A large majority of observed K65R cases were explained by the use of tenofovir, reflecting its wide use in clinical practice. However, changing patterns over time in NRTIs accompanying tenofovir resulted in a persistent decreasing probability of K65R selection by tenofovir-based therapy. The currently recommended NRTI combination tenofovir/emtricitabine was associated with a low probability of K65R emergence. For any given dual NRTI combination including tenofovir, higher selection rates of K65R were consistently observed with a non-nucleoside reverse transcriptase inhibitor than with a protease inhibitor as the third agent. Discussion Our finding of a stable time trend of K65R despite elevated use of tenofovir illustrates increased potency of current HIV-1 therapy including tenofovir. PMID:23027713

  14. Suspected nosocomial infections with multi-drug resistant E. coli, including extended-spectrum beta-lactamase (ESBL)-producing strains, in an equine clinic.

    PubMed

    Walther, Birgit; Lübke-Becker, Antina; Stamm, Ivonne; Gehlen, Heidrun; Barton, Ann Kristin; Janssen, Traute; Wieler, Lothar H; Guenther, Sebastian

    2014-01-01

    Enterobacteriaceae such as Escherichia coli are common commensals as well as opportunistic and obligate pathogens. They cause a broad spectrum of infectious diseases in various hosts, including hospital-associated infections. In recent years, the rise of extended spectrum beta-lactamase (ESBL)-producing E. coli in companion animals (dogs, cats and horses) has been striking. However, reports on nosocomial infections are mostly anecdotic. Here we report on the suspected nosocomial spread of both ESBL-producing and non-ESBL-producing multi-drug resistant E. coli isolates in three equine patients within an equine clinic. Unlike easy-to-clean hospitalization opportunities available for small animal settings like boxes and cages made of ceramic floor tiles or stainless steel, clinical settings for horses are challenging environments for infection control programs due to unavoidable extraneous material including at least hay and materials used for horse bedding. The development of practice-orientated recommendations is needed to improve the possibilities for infection control to prevent nosocomial infections with multi-drug resistant and other transmissible pathogens in equine clinical settings.

  15. FTE Dependence on IMF Orientation and Presence of Hall Physics in Global MHD Simulations

    NASA Astrophysics Data System (ADS)

    Maynard, K. M.; Germaschewski, K.; Lin, L.; Raeder, J.

    2013-12-01

    Flux Transfer Events (FTEs) are poleward traveling flux ropes that form in the dayside magnetopause and represent significant coupling of the solar wind to the magnetosphere during times of southward IMF. In the 35 years since their discovery, FTEs have been extensively observed and modeled; however, there is still no consensus on their generation mechanism. Previous modeling efforts have shown that FTE occurrence and size depend on the resistivity model that is used in simulations and the structure of X-lines in the magnetopause. We use Hall OpenGGCM, a global Hall-MHD code, to study the formation and propagation of FTEs in the dayside magnetopause using synthetic solar wind conditions. We examine large scale FTE structure and nearby magnetic separators for a range of IMF clock angles and dipole tilts. In addition, we investigate how FTE formation and recurrence rate depends on the presence of the Hall term in the generalized Ohm's law compared with resistive MHD.

  16. Calculation of Magnetospheric Equilibria and Evolution of Plasma Bubbles with a New Finite-Volume MHD/Magnetofriction Code

    NASA Astrophysics Data System (ADS)

    Silin, I.; Toffoletto, F.; Wolf, R.; Sazykin, S. Y.

    2013-12-01

    We present a finite-volume MHD code for simulations of magnetospheric dynamics of the plasma sheet and the inner magnetosphere. The code uses staggered non-uniform Cartesian grids to preserve the divergence-free magnetic fields, along with various numerical approximations and flux limiters for the plasma variables. The code can be initialized with empirical magnetic field models, such as the Tsyganenko models along with pressure information from either the Tsyganenko-Mukai models, or observational data, such as DMSP pressure maps. Artificial "friction term" can be added to the momentum equation, which turns the MHD code into "magnetofriction" code which can be used to construct approximate equilibrium solutions. We demonstrate some applications for our code, in both the "magnetofriction" and MHD mode, including relaxation of the empirical models to equilibrium and the evolution of a plasma bubble in the near magnetotail. The latter MHD simulation results exhibit oscillations about their equilibrium position in agreement with recent observations.

  17. Conceptual design study of potential early commercial MHD powerplant. Report of task 2 results

    NASA Astrophysics Data System (ADS)

    Hals, F. A.

    1981-03-01

    The conceptual design of one of the potential early commercial MHD power plants was studied. The plant employs oxygen enrichment of the combustion air and preheating of this oxygen enriched air to an intermediate temperature of 1200 F attainable with a tubular type recuperative heat exchanger. Conceptual designs of plant componets and equipment with performance, operational characteristics, and costs are reported. Plant economics and overall performance including full and part load operation are reviewed. The projected performance and estimated cost of this early MHD plant are compared to conventional power plants, although it does not offer the same high efficiency and low costs as the mature MHD power plant. Environmental aspects and the methods incorporated in plant design for emission control of sulfur and nitrogen are reviewed.

  18. Conceptual design study of potential early commercial MHD powerplant. Report of task 2 results

    NASA Technical Reports Server (NTRS)

    Hals, F. A.

    1981-01-01

    The conceptual design of one of the potential early commercial MHD power plants was studied. The plant employs oxygen enrichment of the combustion air and preheating of this oxygen enriched air to an intermediate temperature of 1200 F attainable with a tubular type recuperative heat exchanger. Conceptual designs of plant componets and equipment with performance, operational characteristics, and costs are reported. Plant economics and overall performance including full and part load operation are reviewed. The projected performance and estimated cost of this early MHD plant are compared to conventional power plants, although it does not offer the same high efficiency and low costs as the mature MHD power plant. Environmental aspects and the methods incorporated in plant design for emission control of sulfur and nitrogen are reviewed.

  19. MHD simulations for investigating interaction processes between a CME and ambient solar wind

    NASA Astrophysics Data System (ADS)

    An, Junmo; Magara, Tetsuya

    2016-05-01

    The interaction between coronal mass ejections (CMEs) and ambient solar winds is one of the important issues of space weather because it affects the trajectory of a flying CME, which determines whether the CME hits the Earth and produces geomagnetic disturbances or not. In this study, two-step 3D magnetohydrodynamic (MHD) simulations including a spheromak-type CME and an ambient solar wind are performed to investigate their interaction processes such as deflection and rotation of a CME. We perform the 1st-step MHD simulation using averaged surface magnetic field data to construct a steady state with an ambient solar wind. A spheromak-type CME is then injected through the solar surface, and subsequent evolution is reproduced by performing the 2nd-step MHD simulation. We discuss key parameters that characterize interaction processes between a CME and ambient solar wind.

  20. MHD Ballooning Instability in the Plasma Sheet

    SciTech Connect

    C.Z. Cheng; S. Zaharia

    2003-10-20

    Based on the ideal-MHD model the stability of ballooning modes is investigated by employing realistic 3D magnetospheric equilibria, in particular for the substorm growth phase. Previous MHD ballooning stability calculations making use of approximations on the plasma compressibility can give rise to erroneous conclusions. Our results show that without making approximations on the plasma compressibility the MHD ballooning modes are unstable for the entire plasma sheet where beta (sub)eq is greater than or equal to 1, and the most unstable modes are located in the strong cross-tail current sheet region in the near-Earth plasma sheet, which maps to the initial brightening location of the breakup arc in the ionosphere. However, the MHD beq threshold is too low in comparison with observations by AMPTE/CCE at X = -(8 - 9)R(sub)E, which show that a low-frequency instability is excited only when beq increases over 50. The difficulty is mitigated by considering the kinetic effects of ion gyrorad ii and trapped electron dynamics, which can greatly increase the stabilizing effects of field line tension and thus enhance the beta(sub)eq threshold [Cheng and Lui, 1998]. The consequence is to reduce the equatorial region of the unstable ballooning modes to the strong cross-tail current sheet region where the free energy associated with the plasma pressure gradient and magnetic field curvature is maximum.

  1. MHD (magnetohydrodynamics) instabilities in simple plasma configuration

    SciTech Connect

    Manheimer, W.M.; Lashmore-Davies, C.

    1984-01-01

    This work provides what, we hope, is a relatively simple, self contained description of MHD instabilities in plasmas with simple configurations. By simple configuration, we mean a plasma in which all quantities vary in only one spatial direction. We deal with such plasmas here because we want to emphasize the basic physics of MHD instabilities. Although some fusion devices are inherently two or three dimensional in nature, there are others, specifically tokamaks and reversed field pinches which are, to good approximation, one dimensional. Also, these devices both display a wealth of complex MHD activity which can be fruitfully discussed. One deceptive aspect of MHD instabilities is that the simplest ones are extremely easy to understand. However more complicated instabilities, for instance in a plasma where both an axial and azimuthal field are present are much more difficult to visualize; but they are also much more interesting. This work is divided into two parts. Chapters 2-9 describe linear theory and chapters 10-15 describe the nonlinear theory. The latter part is naturally much more speculative than the former because less is known about nonlinear theory.

  2. Robust and Efficient Riemann Solvers for MHD

    NASA Astrophysics Data System (ADS)

    Miyoshi, T.; Kusano, K.

    2008-04-01

    Robust and efficient approximate Riemann solvers for magnetohydrodynamics (MHD) are constructed. Particularly, a family of positively conservative Harten-Lax-van Leer (HLL)-type Riemann solvers, the so-called HLLD (`D' denotes Discontinuities), HLLR (`R' denotes Rotational), HLLC (`C' denotes Contact), and HLL solvers, is systematically considered.

  3. Featured Image: Tests of an MHD Code

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-09-01

    Creating the codes that are used to numerically model astrophysical systems takes a lot of work and a lot of testing! A new, publicly available moving-mesh magnetohydrodynamics (MHD) code, DISCO, is designed to model 2D and 3D orbital fluid motion, such as that of astrophysical disks. In a recent article, DISCO creator Paul Duffell (University of California, Berkeley) presents the code and the outcomes from a series of standard tests of DISCOs stability, accuracy, and scalability.From left to right and top to bottom, the test outputs shown above are: a cylindrical Kelvin-Helmholtz flow (showing off DISCOs numerical grid in 2D), a passive scalar in a smooth vortex (can DISCO maintain contact discontinuities?), a global look at the cylindrical Kelvin-Helmholtz flow, a Jupiter-mass planet opening a gap in a viscous disk, an MHD flywheel (a test of DISCOs stability), an MHD explosion revealing shock structures, an MHD rotor (a more challenging version of the explosion), a Flock 3D MRI test (can DISCO study linear growth of the magnetorotational instability in disks?), and a nonlinear 3D MRI test.Check out the gif below for a closer look at each of these images, or follow the link to the original article to see even more!CitationPaul C. Duffell 2016 ApJS 226 2. doi:10.3847/0067-0049/226/1/2

  4. Three-fluid, 3D MHD solar wind modeling with turbulence transport and eddy viscosity

    NASA Astrophysics Data System (ADS)

    Usmanov, A. V.; Goldstein, M. L.; Matthaeus, W. H.

    2014-12-01

    We present results from a three-fluid, fully three-dimensional MHD solar wind model that includes turbulence transport, eddy viscosity, turbulent resistivity, and turbulent heating. The solar wind plasma is described as a co-moving system of three species: the solar wind protons, electrons, and interstellar pickup protons. Separate energy equations are employed for each species. We obtain numerical solutions of Reynolds-averaged solar wind equations coupled with turbulence transport equations in the region from 0.3 to 100 AU. The integrated system of equations includes 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. 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 turbulence parameters, throughout the heliosphere. The model results are compared with observations on WIND, Ulysses and Voyager 2 spacecraft. This work is partially supported by LWS and Heliophysics Grand Challenges programs.

  5. Statistical properties of MHD fluctuations associated with high speed streams from HELIOS 2 observations

    NASA Technical Reports Server (NTRS)

    Bavassano, B.; Dobrowolny, H.; Fanfoni, G.; Mariani, F.; Ness, N. F.

    1981-01-01

    Helios 2 magnetic data were used to obtain several statistical properties of MHD fluctuations associated with the trailing edge of a given stream served in different solar rotations. Eigenvalues and eigenvectors of the variance matrix, total power and degree of compressibility of the fluctuations were derived and discussed both as a function of distance from the Sun and as a function of the frequency range included in the sample. The results obtained add new information to the picture of MHD turbulence in the solar wind. In particular, a dependence from frequency range of the radial gradients of various statistical quantities is obtained.

  6. Effects of centrifugal modification of magnetohydrodynamic equilibrium on resistive wall mode stability

    NASA Astrophysics Data System (ADS)

    Shiraishi, J.; Aiba, N.; Miyato, N.; Yagi, M.

    2014-08-01

    Toroidal rotation effects are self-consistently taken into account not only in the linear magnetohydrodynamic (MHD) stability analysis but also in the equilibrium calculation. The MHD equilibrium computation is affected by centrifugal force due to the toroidal rotation. To study the toroidal rotation effects on resistive wall modes (RWMs), a new code has been developed. The RWMaC modules, which solve the electromagnetic dynamics in vacuum and the resistive wall, have been implemented in the MINERVA code, which solves the Frieman-Rotenberg equation that describes the linear ideal MHD dynamics in a rotating plasma. It is shown that modification of MHD equilibrium by the centrifugal force significantly reduces growth rates of RWMs with fast rotation in the order of M2 = 0.1 where M is the Mach number. Moreover, it can open a stable window which does not exist under the assumption that the rotation affects only the linear dynamics. The rotation modifies the equilibrium pressure gradient and current density profiles, which results in the change of potential energy including rotational effects.

  7. 3-D MHD Simulation of Oscillating Field Current Drive

    NASA Astrophysics Data System (ADS)

    Ebrahimi, F.; Prager, S. C.; Wright, J. C.

    2000-10-01

    Oscillating Field Current Drive (OFCD) is a proposed low frequency steady-state current drive technique for the Reversed Field Pinch (RFP). In OFCD toroidal and poloidal oscillating electric fields are applied with 90^circ phase difference to inject magnetic helicity. In the present work, the 3-D nonlinear, resistive MHD code DEBS is used to simulate OFCD in relaxed RFP plasmas. The present simulations are at high Lundquist number S=10^5 and low spect ratio R/a=1.5. The physics issues investigated are the response of background magnetic fluctuations to the oscillating fields, the relative contributions of the tearing mode dynamo and the oscillating fields to the current profile, and the sustainment and control of the steady-state current profile. Initial results with low amplitude oscillating fields show the expected increase in magnetic helicity and current. Results with higher amplitude will also be presented.

  8. Gonorrhoea and gonococcal antimicrobial resistance surveillance networks in the WHO European Region, including the independent countries of the former Soviet Union.

    PubMed

    Unemo, Magnus; Ison, Catherine A; Cole, Michelle; Spiteri, Gianfranco; van de Laar, Marita; Khotenashvili, Lali

    2013-12-01

    Antimicrobial resistance (AMR) in Neisseria gonorrhoeae has emerged for essentially all antimicrobials following their introduction into clinical practice. During the latest decade, susceptibility to the last remaining options for antimicrobial monotherapy, the extended-spectrum cephalosporins (ESC), has markedly decreased internationally and treatment failures with these ESCs have been verified. In response to this developing situation, WHO and the European Centre for Disease Prevention and Control (ECDC) have published global and region-specific response plans, respectively. One main component of these action/response plans is to enhance the surveillance of AMR and treatment failures. This paper describes the perspectives from the diverse WHO European Region (53 countries), including the independent countries of the former Soviet Union, regarding gonococcal AMR surveillance networks. The WHO European Region has a high prevalence of resistance to all previously recommended antimicrobials, and most of the first strictly verified treatment failures with cefixime and ceftriaxone were also reported from Europe. In the European Union/European Economic Area (EU/EEA), the European gonococcal antimicrobial surveillance programme (Euro-GASP) funded by the ECDC is running. In 2011, the Euro-GASP included 21/31 (68%) EU/EEA countries, and the programme is further strengthened annually. However, in the non-EU/EEA countries, internationally reported and quality assured gonococcal AMR data are lacking in 87% of the countries and, worryingly, appropriate support for establishment of a GASP is still lacking. Accordingly, national and international support, including political and financial commitment, for gonococcal AMR surveillance in the non-EU/EEA countries of the WHO European Region is essential.

  9. Symmetry, Statistics and Structure in MHD Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2007-01-01

    Here, we examine homogeneous MHD turbulence in terms of truncated Fourier series. The ideal MHD equations and the associated statistical theory of absolute equilibrium ensembles are symmetric under P, C and T. However, the presence of invariant helicities, which are pseudoscalars under P and C, dynamically breaks this symmetry. This occurs because the surface of constant energy in phase space has disjoint parts, called components: while ensemble averages are taken over all components, a dynamical phase trajectory is confined to only one component. As the Birkhoff-Khinchin theorem tells us, ideal MHD turbulence is thus non-ergodic. This non-ergodicity manifests itself in low-wave number Fourier modes that have large mean values (while absolute ensemble theory predicts mean values of zero). Therefore, we have coherent structure in ideal MHD turbulence. The level of non-ergodicity and amount of energy contained in the associated coherent structure depends on the values of the helicities, as well as on the presence, or not, of a mean magnetic field and/or overall rotation. In addition to the well known cross and magnetic helicities, we also present a new invariant, which we call the parallel helicity, since it occurs when mean field and rotation axis are aligned. The question of applicability of these results to real (i.e., dissipative) MHD turbulence is also examined. Several long-time numerical simulations on a 64(exp 3) grid are given as examples. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection of these results with inverse spectral cascades, selective decay, and magnetic dynamos is also discussed.

  10. MHD modeling of DIII-D QH-mode discharges and comparison to observations

    NASA Astrophysics Data System (ADS)

    King, Jacob

    2016-10-01

    MHD modeling of DIII-D QH-mode discharges and comparison to observations Nonlinear NIMROD simulations, initialized from a reconstruction of a DIII-D QH-mode discharge with broadband MHD, saturate into a turbulent state, but do not saturate when flow is not included. This is consistent with the experimental results of the quiescent regime observed on DIII-D with broadband MHD activity [Garofalo et al., PoP (2015) and refs. within]. These ELM-free discharges have the normalized pedestal-plasma confinement necessary for burning-plasma operation on ITER. Relative to QH-mode operation with more coherent MHD activity, operation with broadband MHD tends to occur at higher densities and lower rotation and thus may be more relevant to ITER. The nonlinear NIMROD simulations require highly accurate equilibrium reconstructions. Our equilibrium reconstructions include the scrape-off-layer profiles and the measured toroidal and poloidal rotation profiles. The simulation develops into a saturated turbulent state and the n=1 and 2 modes become dominant through an inverse cascade. Each toroidal mode in the range of n=1-5 is dominant at a different time. The perturbations are advected and sheared apart in the counter-clockwise direction consistent with the direction of the poloidal flow inside the LCFS. Work towards validation through comparison to magnetic coil and Doppler reflectometry measurements is presented. Consistent with experimental observations during QH-mode, the simulated state leads to large particle transport relative to the thermal transport. Analysis shows that the phase of the density and temperature perturbations differ resulting in greater convective particle transport relative to the convective thermal transport. This work supported by the U.S. Department of Energy Office of Science and the SciDAC Center for Extended MHD Modeling under Contract Numbers DE-FC02-06ER54875, DE-FC02-08ER54972 and DE-FC02-04ER54698.

  11. Self-consistent stationary MHD shear flows in the solar atmosphere as electric field generators

    NASA Astrophysics Data System (ADS)

    Nickeler, D. H.; Karlický, M.; Wiegelmann, T.; Kraus, M.

    2014-09-01

    Context. Magnetic fields and flows in coronal structures, for example, in gradual phases in flares, can be described by 2D and 3D magnetohydrostatic (MHS) and steady magnetohydrodynamic (MHD) equilibria. Aims: Within a physically simplified, but exact mathematical model, we study the electric currents and corresponding electric fields generated by shear flows. Methods: Starting from exact and analytically calculated magnetic potential fields, we solved the nonlinear MHD equations self-consistently. By applying a magnetic shear flow and assuming a nonideal MHD environment, we calculated an electric field via Faraday's law. The formal solution for the electromagnetic field allowed us to compute an expression of an effective resistivity similar to the collisionless Speiser resistivity. Results: We find that the electric field can be highly spatially structured, or in other words, filamented. The electric field component parallel to the magnetic field is the dominant component and is high where the resistivity has a maximum. The electric field is a potential field, therefore, the highest energy gain of the particles can be directly derived from the corresponding voltage. In our example of a coronal post-flare scenario we obtain electron energies of tens of keV, which are on the same order of magnitude as found observationally. This energy serves as a source for heating and acceleration of particles.

  12. Integron, Plasmid and Host Strain Characteristics of Escherichia coli from Humans and Food Included in the Norwegian Antimicrobial Resistance Monitoring Programs

    PubMed Central

    Sunde, Marianne; Simonsen, Gunnar Skov; Slettemeås, Jannice Schau; Böckerman, Inger; Norström, Madelaine

    2015-01-01

    Antimicrobial resistant Escherichia coli (n=331) isolates from humans with bloodstream infections were investigated for the presence of class 1 and class 2 integrons. The integron cassettes arrays were characterized and the findings were compared with data from similar investigations on resistant E. coli from meat and meat products (n=241) produced during the same time period. All isolates were obtained from the Norwegian monitoring programs for antimicrobial resistance in human pathogens and in the veterinary sector. Methods used included PCR, sequencing, conjugation experiments, plasmid replicon typing and subtyping, pulsed-field-gel-electrophoresis and serotyping. Integrons of class 1 and 2 occurred significantly more frequently among human isolates; 45.4% (95% CI: 39.9-50.9) than among isolates from meat; 18% (95% CI: 13.2 -23.3), (p<0.01, Chi-square test). Identical cassette arrays including dfrA1-aadA1, aadA1, dfrA12-orfF-aadA2, oxa-30-aadA1 (class 1 integrons) and dfrA1-sat1-aadA1 (class 2 integrons) were detected from both humans and meat. However, the most prevalent cassette array in human isolates, dfrA17-aadA5, did not occur in isolates from meat, suggesting a possible linkage between this class 1 integron and a subpopulation of E. coli adapted to a human host. The drfA1-aadA1 and aadA1 class 1 integrons were found frequently in both human and meat isolates. These isolates were subjected to further studies to investigate similarities with regard to transferability, plasmid and host strain characteristics. We detected incF plasmids with pMLST profile F24:A-:B1 carrying drfA1-aadA1 integrons in isolates from pork and in a more distantly related E. coli strain from a human with septicaemia. Furthermore, we showed that most of the class 1 integrons with aadA1 were located on incF plasmids with pMLST profile F51:A-:B10 in human isolates. The plasmid was present in unrelated as well as closely related host strains, demonstrating that dissemination of this

  13. Efficacy, safety, and tolerability of a 24-month treatment regimen including delamanid in a child with extensively drug-resistant tuberculosis

    PubMed Central

    Esposito, Susanna; Bosis, Samantha; Tadolini, Marina; Bianchini, Sonia; Migliori, Giovanni Battista; Principi, Nicola

    2016-01-01

    Abstract Rational: Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) are emerging problems in several countries. These infections require long and expensive treatment regimens. Recently, 2 new drugs, bedaquiline and delamanid, have been approved in several countries for use in adults with severe, difficult-to-treat MDR-TB, and it has been suggested that they could also be administered to children with MDR-TB and limited treatment options. However, no study has been completed on their efficacy. Patient concerns: This report describes a 12-year-old child with XDR-TB who was cured after a 24-month therapy regimen, which included delamanid. Diagnoses: The patient showed progressive clinical deterioration after 5 months of treatment with the majority of anti-TB drugs available on the market. Interventions: After unsuccessfull treatment with several anti-TB drugs for 5 months, he was treated with a regimen including for 24 months. Outcomes: Direct smear microscopy of the gastric aspirates and gastric aspirate cultures for Mycobacterium tuberculosis became negative after only 1 week and remained persistently negative. During the 24-month treatment, all blood test results remained within the normal range, no adverse events were reported, and corrected QT interval was always normal. A clinical and laboratory control was performed 3 months after discontinuation of delamanid, and the other drugs did not reveal any modification of both general conditions as well as laboratory and radiological findings. The patient was considered cured. Lessons: The positive outcome associated with the favorable safety and tolerability profile showed that long-term therapy with delamanid can significantly contribute to treating apparently hopeless XDR-TB cases in children. PMID:27861363

  14. Genotypic and Antimicrobial Susceptibility of Carbapenem-resistant Acinetobacter baumannii: Analysis of ISAba Elements and blaOXA-23-like Genes Including a New Variant

    PubMed Central

    Bahador, Abbas; Raoofian, Reza; Pourakbari, Babak; Taheri, Mohammad; Hashemizadeh, Zahra; Hashemi, Farhad B.

    2015-01-01

    Carbapenem-resistant Acinetobacter baumannii (CR-AB) causes serious nosocomial infections, especially in ICU wards of hospitals, worldwide. Expression of blaOXA genes is the chief mechanism of conferring carbapenem resistance among CR-AB. Although some blaOXA genes have been studied among CR-AB isolates from Iran, their blaOXA-23-like genes have not been investigated. We used a multiplex-PCR to detect Ambler class A, B, and D carbapenemases of 85 isolates, and determined that 34 harbored blaOXA-23-like genes. Amplified fragment length polymorphism (AFLP) genotyping, followed by DNA sequencing of blaOXA-23-like amplicons of CR-AB from each AFLP group was used to characterize their blaOXA-23-like genes. We also assessed the antimicrobial susceptibility pattern of CR-AB isolates, and tested whether they harbored insertion sequences ISAba1 and ISAba4. Sequence comparison with reference strain A. baumannii (NCTC12156) revealed five types of mutations in blaOXA-23-like genes; including one novel variant and four mutants that were already reported from China and the USA. All of the blaOXA-23-like genes mutations were associated with increased minimum inhibitory concentrations (MICs) against imipenem. ISAba1 and ISAba4 sequences were detected upstream of blaOXA-23 genes in 19 and 7% of isolates, respectively. The isolation of CR-AB with new blaOXA-23 mutations including some that have been reported from the USA and China highlights CR-AB pervasive distribution, which underscores the importance of concerted national and global efforts to control the spread of CR-AB isolates worldwide. PMID:26617588

  15. Genotypic and Antimicrobial Susceptibility of Carbapenem-resistant Acinetobacter baumannii: Analysis of is Aba Elements and bla OXA-23-like Genes Including a New Variant.

    PubMed

    Bahador, Abbas; Raoofian, Reza; Pourakbari, Babak; Taheri, Mohammad; Hashemizadeh, Zahra; Hashemi, Farhad B

    2015-01-01

    Carbapenem-resistant Acinetobacter baumannii (CR-AB) causes serious nosocomial infections, especially in ICU wards of hospitals, worldwide. Expression of bla OXA genes is the chief mechanism of conferring carbapenem resistance among CR-AB. Although some bla OXA genes have been studied among CR-AB isolates from Iran, their bla OXA-23-like genes have not been investigated. We used a multiplex-PCR to detect Ambler class A, B, and D carbapenemases of 85 isolates, and determined that 34 harbored bla OXA-23-like genes. Amplified fragment length polymorphism (AFLP) genotyping, followed by DNA sequencing of bla OXA-23-like amplicons of CR-AB from each AFLP group was used to characterize their bla OXA-23-like genes. We also assessed the antimicrobial susceptibility pattern of CR-AB isolates, and tested whether they harbored insertion sequences ISAba1 and ISAba4. Sequence comparison with reference strain A. baumannii (NCTC12156) revealed five types of mutations in bla OXA-23-like genes; including one novel variant and four mutants that were already reported from China and the USA. All of the bla OXA-23-like genes mutations were associated with increased minimum inhibitory concentrations (MICs) against imipenem. ISAba1 and ISAba4 sequences were detected upstream of bla OXA-23 genes in 19 and 7% of isolates, respectively. The isolation of CR-AB with new bla OXA-23 mutations including some that have been reported from the USA and China highlights CR-AB pervasive distribution, which underscores the importance of concerted national and global efforts to control the spread of CR-AB isolates worldwide.

  16. MHD simulations of magnetized laser-plasma interaction for laboratory astrophysics

    NASA Astrophysics Data System (ADS)

    Khiar, Benjamin; Ciardi, Andrea; Vinci, Tommaso; Revet, Guilhem; Fuchs, Julien; Higginson, Drew

    2015-11-01

    Laser-driven plasmas coupled with externally applied strong, steady-state, magnetic fields have applications that range from ICF to astrophysical studies of jet collimation, accretion shock dynamics in young stars and streaming instabilities in space plasmas. We have recently included the modelling of laser energy deposition in our three-dimensional, resistive two-temperature MHD code GORGON. The model assumes linear inverse-bremsstrahlung absorption and the laser propagation is done in the geometrical optics approximation. We present full scale numerical simulations of actual experiments performed on the ELFIE installation at LULI, including plasma generated from single and multiple laser plasmas embedded in a magnetic field of strength up to 20 T, and experiments and astrophysical simulations that have shown the viability of poloidal magnetic fields to directly result in the collimation of outflows and the formation of jets in astrophysical accreting systems, such as in young stellar objects. The authors acknowledge the support from the Ile-de-France DIM ACAV, from the LABEX Plas@par and from the ANR grant SILAMPA.

  17. Energy storage and dissipation in the magnetotail during substorms. 2. MHD simulations

    SciTech Connect

    Steinolfson, R.S. ); Winglee, R.M. )

    1993-05-01

    The authors present a global MHD simulation of the magnetotail in an effort to study magnetic storm development. They address the question of energy storage in the current sheet in the early phases of storm growth, which previous simulations have not shown. They address this problem by dealing with the variation of the resistivity throughout the magnetosphere. They argue that MHD theory should provide a suitable representation to this problem on a global scale, even if it does not handle all details adequately. For their simulation they use three different forms for the resistivity. First is a uniform and constant resistivity. Second is a resistivity proportional to the current density, which is related to argument that resistivity is driven by wave-particle interactions which should be strongest in regions where the current is the greatest. Thirdly is a model where the resistivity varies with the magnetic field strength, which was suggested by previous results from particle simulations of the same problem. The simulation then gives approximately the same response of the magnetosphere for all three of the models. Each results in the formation and ejection of plasmoids, but the energy stored in the magnetotail, the timing of substorm onset in relation to the appearance of a southward interplanetary magnetic field, and the speed of ejection of the plasmoids formed differ with the resistivity models.

  18. Numerical MHD codes for modeling astrophysical flows

    NASA Astrophysics Data System (ADS)

    Koldoba, A. V.; Ustyugova, G. V.; Lii, P. S.; Comins, M. L.; Dyda, S.; Romanova, M. M.; Lovelace, R. V. E.

    2016-05-01

    We describe a Godunov-type magnetohydrodynamic (MHD) code based on the Miyoshi and Kusano (2005) solver which can be used to solve various astrophysical hydrodynamic and MHD problems. The energy equation is in the form of entropy conservation. The code has been implemented on several different coordinate systems: 2.5D axisymmetric cylindrical coordinates, 2D Cartesian coordinates, 2D plane polar coordinates, and fully 3D cylindrical coordinates. Viscosity and diffusivity are implemented in the code to control the accretion rate in the disk and the rate of penetration of the disk matter through the magnetic field lines. The code has been utilized for the numerical investigations of a number of different astrophysical problems, several examples of which are shown.

  19. Amplitudes of MHD Waves in Sunspots

    NASA Astrophysics Data System (ADS)

    Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint, Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.; Rajaguru, Paul

    2016-05-01

    The conversion of p-modes into MHD waves by strong magnetic fields occurs mainly in the sub-photospheric layers. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on small amplitude oscillations observed in the photosphere with Hinode SOT/SP in which we analyze time series for sunspots ARs 12186 (11.10.2014) and 12434 (17.10.2015). No significant magnetic field oscillations are recovered in the umbra or penumbra in the ME inversion. However, periodicities in the inclination angle are found at the umbral/penumbral boundary with 5 minute periods. Upward propagating waves are indicated in the intensity signals correlated between HMI and AIA at different heights. We compare SP results with the oscillations observed in HMI data. Simultaneous IRIS data shows transition region brightening above the umbral core.

  20. MHD processes in the outer heliosphere

    NASA Technical Reports Server (NTRS)

    Burlaga, L. F.

    1984-01-01

    The magnetic field measurements from Voyager and the magnetohydrodynamic (MHD) processes in the outer heliosphere are reviewed. A bibliography of the experimental and theoretical work concerning magnetic fields and plasmas observed in the outer heliosphere is given. Emphasis in this review is on basic concepts and dynamical processes involving the magnetic field. The theory that serves to explain and unify the interplanetary magnetic field and plasma observations is magnetohydrodynamics. Basic physical processes and observations that relate directly to solutions of the MHD equations are emphasized, but obtaining solutions of this complex system of equations involves various assumptions and approximations. The spatial and temporal complexity of the outer heliosphere and some approaches for dealing with this complexity are discussed.

  1. Coherent Eigenmodes in Homogeneous MHD Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2010-01-01

    The statistical mechanics of Fourier models of ideal, homogeneous, incompressible magnetohydrodynamic (MHD) turbulence is discussed, along with their relevance for dissipative magnetofluids. Although statistical theory predicts that Fourier coefficients of fluid velocity and magnetic field are zero-mean random variables, numerical simulations clearly show that certain coefficients have a non-zero mean value that can be very large compared to the associated standard deviation, i.e., we have coherent structure. We use eigenanalysis of the modal covariance matrices in the probability density function to explain this phenomena in terms of `broken ergodicity', which is defined to occur when dynamical behavior does not match ensemble predictions on very long time-scales. We provide examples from 2-D and 3-D magnetohydrodynamic simulations of homogeneous turbulence, and show new results from long-time simulations of MHD turbulence with and without a mean magnetic field

  2. MHD shocks in coronal mass ejections

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1991-01-01

    The primary objective of this research program is the study of the magnetohydrodynamic (MHD) shocks and nonlinear simple waves produced as a result of the interaction of ejected lower coronal plasma with the ambient corona. The types of shocks and nonlinear simple waves produced for representative coronal conditions and disturbance velocities were determined. The wave system and the interactions between the ejecta and ambient corona were studied using both analytic theory and numerical solutions of the time-dependent, nonlinear MHD equations. Observations from the SMM coronagraph/polarimeter provided both guidance and motivation and are used extensively in evaluating the results. As a natural consequence of the comparisons with the data, the simulations assisted in better understanding the physical interactions in coronal mass ejections (CME's).

  3. Analytical investigation of critical MHD phenomena

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Development and analysis of schemes for suppression of the startup overvoltage transient in the AEDC High Performance Demonstration Experiment (HPDE), analysis of performance enhancement due to electrode voltage drop reduction by use of pyrolytic graphites in the HPDE, prediction of optimal loading schemes for the HPDE, prediction of PHDE performance with a diagonal electrical connection, and predictions of the likelihood and effects of axial current leakage between adjacent electrodes in the HPDE are reviewed. Simulations of tests at the AEDC/HPDE with STD Research Corporation multidimensional and time dependent computer codes provided additional validation for the computer codes and shed light on physical mechanisms which govern performance and durability of MHD power generators. The magnetoaerothermal effect was predicted by STD Research Corporation to have a significant effect on the HPDE/MHD generator performance at high interaction.

  4. Inductive-dynamic magnetosphere-ionosphere coupling via MHD waves

    NASA Astrophysics Data System (ADS)

    Tu, Jiannan; Song, Paul; Vasyliūnas, Vytenis M.

    2014-01-01

    In the present study, we investigate magnetosphere-ionosphere/thermosphere (M-IT) coupling via MHD waves by numerically solving time-dependent continuity, momentum, and energy equations for ions and neutrals, together with Maxwell's equations (Ampère's and Faraday's laws) and with photochemistry included. This inductive-dynamic approach we use is fundamentally different from those in previous magnetosphere-ionosphere (M-I) coupling models: all MHD wave modes are retained, and energy and momentum exchange between waves and plasma are incorporated into the governing equations, allowing a self-consistent examination of dynamic M-I coupling. Simulations, using an implicit numerical scheme, of the 1-D ionosphere/thermosphere system responding to an imposed convection velocity at the top boundary are presented to show how magnetosphere and ionosphere are coupled through Alfvén waves during the transient stage when the IT system changes from one quasi steady state to another. Wave reflection from the low-altitude ionosphere plays an essential role, causing overshoots and oscillations of ionospheric perturbations, and the dynamical Hall effect is an inherent aspect of the M-I coupling. The simulations demonstrate that the ionosphere/thermosphere responds to magnetospheric driving forces as a damped oscillator.

  5. MHD (magnetohydrodynamic) undersea propulsion: A novel concept with renewed interest

    SciTech Connect

    Doss, E.D.; Geyer, H.K. ); Roy, G.D. )

    1990-01-01

    This paper discusses the reasons for the national and international renewed interest in the concept of MHD seawater propulsion. The main advantages of this concept are presented, together with some of the technical challenges that need to be overcome to achieve reliability, performance, and stealth. The paper discusses in more detail some of the technical issues and loss mechanisms influencing the thruster performance in terms of its electrical efficiency. Among the issues discussed are the jet losses and nozzle efficiency. Ohmic losses and frictional losses inside the thruster. Also discussed are the electrical end losses caused by the fringing magnetic field near the end of the electrodes. It has been shown that the frictional and end losses can have strong adverse effects on the thruster performance. Furthermore, a parametric study has been performed to investigate the effects of several parameters on the performance of the MHD thrusters. Those parameters include the magnetic field, thruster diameter, all roughness, flow velocity, and electrical load factor. The results of the parametric study indicate that the thruster efficiency increases with the strength of the magnetic field and thruster diameter, and decreases with the wall roughness and the flow velocity. 8 refs., 8 figs.

  6. An Unsplit, Cell-Centered Godunov Method for Ideal MHD

    SciTech Connect

    Fisher, R; Crockett, R; Colella, P; Klein, R; McKee, C

    2003-10-16

    We present a second-order Godunov algorithm for multidimensional, ideal MHD. Our algorithm is based on the unsplit formulation of Colella, with all of the primary dependent variables centered at the same location. To properly represent the divergence-free condition of the magnetic fields, we apply a discrete projection to the intermediate values of the field at cell faces, and apply a filter to the primary dependent variables at the end of each time step. We apply the method to a suite of linear and nonlinear tests to ascertain accuracy and stability of the scheme under a variety of conditions. The test suite includes rotated planar linear waves, MHD shock tube problems, and low-beta flux tubes. For all of these cases, we observe that the algorithm is second-order accurate for smooth solutions, converges to the correct weak solution for problems involving shocks, and exhibits no evidence of instability or loss of accuracy due to the possible presence of non-solenoidal fields.

  7. An unsplit, cell-centered Godunov method for ideal MHD

    SciTech Connect

    Crockett, Robert K.; Colella, Phillip; Fisher, Robert T.; Klein, Richard I.; McKee, Christopher F.

    2003-08-29

    We present a second-order Godunov algorithm for multidimensional, ideal MHD. Our algorithm is based on the unsplit formulation of Colella (J. Comput. Phys. vol. 87, 1990), with all of the primary dependent variables centered at the same location. To properly represent the divergence-free condition of the magnetic fields, we apply a discrete projection to the intermediate values of the field at cell faces, and apply a filter to the primary dependent variables at the end of each time step. We test the method against a suite of linear and nonlinear tests to ascertain accuracy and stability of the scheme under a variety of conditions. The test suite includes rotated planar linear waves, MHD shock tube problems, low-beta flux tubes, and a magnetized rotor problem. For all of these cases, we observe that the algorithm is second-order accurate for smooth solutions, converges to the correct weak solution for problems involving shocks, and exhibits no evidence of instability or loss of accuracy due to the possible presence of non-solenoidal fields.

  8. Capabilities of Fully Parallelized MHD Stability Code MARS

    NASA Astrophysics Data System (ADS)

    Svidzinski, Vladimir; Galkin, Sergei; Kim, Jin-Soo; Liu, Yueqiang

    2016-10-01

    Results of full parallelization of the plasma stability code MARS will be reported. MARS calculates eigenmodes in 2D axisymmetric toroidal equilibria in MHD-kinetic plasma models. Parallel version of MARS, named PMARS, has been recently developed at FAR-TECH. Parallelized MARS is an efficient tool for simulation of MHD instabilities with low, intermediate and high toroidal mode numbers within both fluid and kinetic plasma models, implemented in MARS. Parallelization of the code included parallelization of the construction of the matrix for the eigenvalue problem and parallelization of the inverse vector iterations algorithm, implemented in MARS for the solution of the formulated eigenvalue problem. Construction of the matrix is parallelized by distributing the load among processors assigned to different magnetic surfaces. Parallelization of the solution of the eigenvalue problem is made by repeating steps of the MARS algorithm using parallel libraries and procedures. Parallelized MARS is capable of calculating eigenmodes with significantly increased spatial resolution: up to 5,000 adapted radial grid points with up to 500 poloidal harmonics. Such resolution is sufficient for simulation of kink, tearing and peeling-ballooning instabilities with physically relevant parameters. Work is supported by the U.S. DOE SBIR program.

  9. Statistical Theory of the Ideal MHD Geodynamo

    NASA Technical Reports Server (NTRS)

    Shebalin, J. V.

    2012-01-01

    A statistical theory of geodynamo action is developed, using a mathematical model of the geodynamo as a rotating outer core containing an ideal (i.e., no dissipation), incompressible, turbulent, convecting magnetofluid. On the concentric inner and outer spherical bounding surfaces the normal components of the velocity, magnetic field, vorticity and electric current are zero, as is the temperature fluctuation. This allows the use of a set of Galerkin expansion functions that are common to both velocity and magnetic field, as well as vorticity, current and the temperature fluctuation. The resulting dynamical system, based on the Boussinesq form of the magnetohydrodynamic (MHD) equations, represents MHD turbulence in a spherical domain. These basic equations (minus the temperature equation) and boundary conditions have been used previously in numerical simulations of forced, decaying MHD turbulence inside a sphere [1,2]. Here, the ideal case is studied through statistical analysis and leads to a prediction that an ideal coherent structure will be found in the form of a large-scale quasistationary magnetic field that results from broken ergodicity, an effect that has been previously studied both analytically and numerically for homogeneous MHD turbulence [3,4]. The axial dipole component becomes prominent when there is a relatively large magnetic helicity (proportional to the global correlation of magnetic vector potential and magnetic field) and a stationary, nonzero cross helicity (proportional to the global correlation of velocity and magnetic field). The expected angle of the dipole moment vector with respect to the rotation axis is found to decrease to a minimum as the average cross helicity increases for a fixed value of magnetic helicity and then to increase again when average cross helicity approaches its maximum possible value. Only a relatively small value of cross helicity is needed to produce a dipole moment vector that is aligned at approx.10deg with the

  10. MHD simulations on an unstructured mesh

    SciTech Connect

    Strauss, H.R.; Park, W.; Belova, E.; Fu, G.Y.; Longcope, D.W.; Sugiyama, L.E.

    1998-12-31

    Two reasons for using an unstructured computational mesh are adaptivity, and alignment with arbitrarily shaped boundaries. Two codes which use finite element discretization on an unstructured mesh are described. FEM3D solves 2D and 3D RMHD using an adaptive grid. MH3D++, which incorporates methods of FEM3D into the MH3D generalized MHD code, can be used with shaped boundaries, which might be 3D.

  11. Laboratory-produced MHD plasma jets

    NASA Astrophysics Data System (ADS)

    Bellan, Paul

    2008-04-01

    Because space plasmas are neither confined by vacuum chamber walls nor have magnetic fields produced by physical coils, space plasmas have shapes that are much less determinate than lab plasmas. An experimental program underway at Caltech produces plasmas where the shape is neither fixed by a vacuum chamber wall nor imposed by an external coil set, but rather is allowed to be determined by self-organizing MHD processes subject to the constraint of imposed boundary conditions analogous to the boundary conditions of space plasmas. These self-organizing processes are believed to be fundamental to astrophysical jets, solar coronal loops, and MHD turbulence (e.g. Taylor relaxation). The experimental dynamics are sufficiently reproducible to allow detailed study despite the morphology being complex and dynamic. A surprising result has been the observation that instead of the plasma uniformly filling up the available volume, the plasma is spatially localized in a highly collimated, small diameter magnetic flux tube, the length and axis of which change in time in response to MHD forces. A model shows that the collimation results from stagnation of linked magnetic flux frozen into a MHD-driven jet that accelerates plasma from the wall into the flux tube, filling the flux tube with plasma. Jet flow has been imaged with a high-speed multi-frame camera, diagnosed via Doppler spectroscopy, and most recently (i) the collision between two opposing, color-coded jets flowing from opposite ends of a flux tube has been observed, and (ii) the collision of a jet with a target cloud has been observed.

  12. Design Study: Rocket Based MHD Generator

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This report addresses the technical feasibility and design of a rocket based MHD generator using a sub-scale LOx/RP rocket motor. The design study was constrained by assuming the generator must function within the performance and structural limits of an existing magnet and by assuming realistic limits on (1) the axial electric field, (2) the Hall parameter, (3) current density, and (4) heat flux (given the criteria of heat sink operation). The major results of the work are summarized as follows: (1) A Faraday type of generator with rectangular cross section is designed to operate with a combustor pressure of 300 psi. Based on a magnetic field strength of 1.5 Tesla, the electrical power output from this generator is estimated to be 54.2 KW with potassium seed (weight fraction 3.74%) and 92 KW with cesium seed (weight fraction 9.66%). The former corresponds to a enthalpy extraction ratio of 2.36% while that for the latter is 4.16%; (2) A conceptual design of the Faraday MHD channel is proposed, based on a maximum operating time of 10 to 15 seconds. This concept utilizes a phenolic back wall for inserting the electrodes and inter-electrode insulators. Copper electrode and aluminum oxide insulator are suggested for this channel; and (3) A testing configuration for the sub-scale rocket based MHD system is proposed. An estimate of performance of an ideal rocket based MHD accelerator is performed. With a current density constraint of 5 Amps/cm(exp 2) and a conductivity of 30 Siemens/m, the push power density can be 250, 431, and 750 MW/m(sup 3) when the induced voltage uB have values of 5, 10, and 15 KV/m, respectively.

  13. Inductive ionospheric solver for magnetospheric MHD simulations

    NASA Astrophysics Data System (ADS)

    Vanhamäki, H.

    2011-01-01

    We present a new scheme for solving the ionospheric boundary conditions required in magnetospheric MHD simulations. In contrast to the electrostatic ionospheric solvers currently in use, the new solver takes ionospheric induction into account by solving Faraday's law simultaneously with Ohm's law and current continuity. From the viewpoint of an MHD simulation, the new inductive solver is similar to the electrostatic solvers, as the same input data is used (field-aligned current [FAC] and ionospheric conductances) and similar output is produced (ionospheric electric field). The inductive solver is tested using realistic, databased models of an omega-band and westward traveling surge. Although the tests were performed with local models and MHD simulations require a global ionospheric solution, we may nevertheless conclude that the new solution scheme is feasible also in practice. In the test cases the difference between static and electrodynamic solutions is up to ~10 V km-1 in certain locations, or up to 20-40% of the total electric field. This is in agreement with previous estimates. It should also be noted that if FAC is replaced by the ground magnetic field (or ionospheric equivalent current) in the input data set, exactly the same formalism can be used to construct an inductive version of the KRM method originally developed by Kamide et al. (1981).

  14. Multi-dimensional MHD simple waves

    SciTech Connect

    Webb, G. M.; Ratkiewicz, R.; Brio, M.; Zank, G. P.

    1996-07-20

    In this paper we consider a formalism for multi-dimensional simple MHD waves using ideas developed by Boillat. For simple wave solutions one assumes that all the physical variables (the density {rho}, gas pressure p, fluid velocity u, gas entropy S, and magnetic induction B in the MHD case) depend on a single phase function {phi}(r,t). The simple wave solution ansatz and the MHD equations then require that the phase function {phi} satisfies an implicit equation of the form f({phi})=r{center_dot}n({phi})-{lambda}({phi})t, where n({phi})={nabla}{phi}/|{nabla}{phi}| is the wave normal, {lambda}({phi})={omega}/k=-{phi}{sub t}/|{nabla}{phi}| is the normal speed of the wave front, and f({phi}) is an arbitrary differentiable function of {phi}. The formalism allows for more general simple waves than that usually dealt with in which n({phi}) is a constant unit vector that does not vary along the wave front. The formalism has implications for shock formation and wave breaking for multi-dimensional waves.

  15. Multi-dimensional MHD simple waves

    NASA Technical Reports Server (NTRS)

    Webb, G. M.; Ratkiewicz, R.; Brio, M.; Zank, G. P.

    1995-01-01

    In this paper we consider a formalism for multi-dimensional simple MHD waves using ideas developed by Boillat. For simple wave solutions one assumes that all the physical variables (the density rho, gas pressure p, fluid velocity V, gas entropy S, and magnetic induction B in the MHD case) depend on a single phase function phi(r,t). The simple wave solution ansatz and the MHD equations then require that the phase function has the form phi = r x n(phi) - lambda(phi)t, where = n(phi) = Delta phi / (absolute value of Delta phi) is the wave normal and lambda(phi) = omega/k = -phi t / (absolute value of Delta phi) is the normal speed of the wave front. The formalism allows for more general simple waves than that usually dealt with in which n(phi) is a constant unit vector that does not vary along the wave front. The formalism has implications for shock formation for multi-dimensional waves.

  16. Building Action Principles for Extended MHD Models

    NASA Astrophysics Data System (ADS)

    Keramidas Charidakos, Ioannis; Lingam, Manasvi; Morrison, Philip; White, Ryan; Wurm, Alexander

    2014-10-01

    The general, non-dissipative, two-fluid model in plasma physics is Hamiltonian, but this property is sometimes lost in the process of deriving simplified two-fluid or one-fluid models from the two-fluid equations of motion. One way to ensure that the reduced models are Hamiltonian is to derive them from an action. We start with the general two-fluid action functional for an electron and an ion fluid interacting with an electromagnetic field, expressed in Lagrangian variables. We perform a change of variables and make various approximations (eg. quasineutrality and ordering of the fields) and small parameter expansions directly in the action. The resulting equations of motion are then mapped to the Eulerian fluid variables using a novel nonlocal Lagrange-Euler map. The correct Eulerian equations are obtained after we impose locality. Using this method and the proper approximations and expansions, we recover Lust's general two-fluid model, extended 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. U.S. Dept. of Energy Contract # DE-FG05-80ET-53088, Western New England University Research Fund.

  17. Fuel conservation and pollution control by MHD

    NASA Astrophysics Data System (ADS)

    Messerle, H. K.; Campbell, B.

    1980-06-01

    MHD generators, which directly convert thermal energy in a fluid into electricity, promise a more effective use of fuel for bulk power production than conventional steam plants, bettering efficiency by over 50% and reducing the generating cost by 20%. Using a Rankine steam cycle, overall power plant efficiency can increase from 33% to 50%, while fuel requirements can be reduced by one third and thermal pollution by one half. Since overall fuel consumption would drop, atmospheric pollution would be decreased, and coal consumption could be diverted to areas where oil is presently being used. The MHD generator structure and operation are discussed, and its general system requirements are explained. A table of energy use and an efficiency graph are provided for comparison purposes. Work is currently being done on a 2 MW open cycle MHD generator at the University of Sydney, Australia, and computer studies are in progress to evaluate the Faraday generator performance for the experimental 2 MW facility and larger power generators with segmented sets of electrodes.

  18. The Statistical Mechanics of Ideal MHD Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2003-01-01

    Turbulence is a universal, nonlinear phenomenon found in all energetic fluid and plasma motion. In particular. understanding magneto hydrodynamic (MHD) turbulence and incorporating its effects in the computation and prediction of the flow of ionized gases in space, for example, are great challenges that must be met if such computations and predictions are to be meaningful. Although a general solution to the "problem of turbulence" does not exist in closed form, numerical integrations allow us to explore the phase space of solutions for both ideal and dissipative flows. For homogeneous, incompressible turbulence, Fourier methods are appropriate, and phase space is defined by the Fourier coefficients of the physical fields. In the case of ideal MHD flows, a fairly robust statistical mechanics has been developed, in which the symmetry and ergodic properties of phase space is understood. A discussion of these properties will illuminate our principal discovery: Coherent structure and randomness co-exist in ideal MHD turbulence. For dissipative flows, as opposed to ideal flows, progress beyond the dimensional analysis of Kolmogorov has been difficult. Here, some possible future directions that draw on the ideal results will also be discussed. Our conclusion will be that while ideal turbulence is now well understood, real turbulence still presents great challenges.

  19. NASA Lewis Research Center combustion MHD experiment

    NASA Astrophysics Data System (ADS)

    Smith, J. M.

    The MHD power generation experiments were conducted in a high field strength cryomagnet which was adapted from an existing facility. In its original construction, it consisted of 12 high purity aluminum coils pool cooled in a bath of liquid neon. In this configuration, a peak field of 15 tesla was produced. For the present experiments, the center four coils were removed and a 23 cm diameter transverse warm bore tube was inserted to allow the placement of the MHD experiment between the remaining eight coils. In this configuration, a peak field of 6 tesla should be obtainable. The time duration of the experiment is limited by the neon supply which allows on the order of 1 minute of total operating time followed by an 18-hour reliquefaction period. As a result, the experiments are run in a pulsed mode. The run duration for the data presented here was 5 sec. The magnetic field profile along the MHD duct is shown. Since the working fluid is in essence superheated steam, it is easily water quenched at the exit of the diffuser and the components are designed vacuum tight so that the exhaust pipe and demister an be pumped down to simulate the vacuum of outer space.

  20. Modeling open boundaries in dissipative MHD simulation

    NASA Astrophysics Data System (ADS)

    Meier, E. T.; Glasser, A. H.; Lukin, V. S.; Shumlak, U.

    2012-04-01

    The truncation of large physical domains to concentrate computational resources is necessary or desirable in simulating many natural and man-made plasma phenomena. Three open boundary condition (BC) methods for such domain truncation of dissipative magnetohydrodynamics (MHD) problems are described and compared here. A novel technique, lacuna-based open boundary conditions (LOBC), is presented for applying open BC to dissipative MHD and other hyperbolic and mixed hyperbolic-parabolic systems of partial differential equations. LOBC, based on manipulating Calderon-type near-boundary sources, essentially damp hyperbolic effects in an exterior region attached to the simulation domain and apply BC appropriate for the remaining parabolic effects (if present) at the exterior region boundary. Another technique, approximate Riemann BC (ARBC), is adapted from finite volume and discontinuous Galerkin methods. In ARBC, the value of incoming flux is specified using a local, characteristic-based method. A third commonly-used open BC, zero-normal derivative BC (ZND BC), is presented for comparison. These open BC are tested in several gas dynamics and dissipative MHD problems. LOBC are found to give stable, low-reflection solutions even in the presence of strong parabolic behavior, while ARBC are stable only when hyperbolic behavior is dominant. Pros and cons of the techniques are discussed and put into context within the body of open BC research to date.

  1. Anisotropic MHD model and some solutions

    SciTech Connect

    Kuznetsov, V. D.; Dzhalilov, N. S.

    2010-09-15

    MHD waves and instabilities in a collisionless anisotropic-pressure plasma are analyzed in an anisotropic MHD model based on the 16-moment approximation, and the results are found to agree well with those obtained in the low-frequency limit of the kinetic model. It is shown that accounting for heat fluxes leads to an asymmetry in the phase velocities of the wave modes with respect to the heat flux direction and also to a strong interaction between the modes, especially between the backward ones (those that propagate in a direction opposite to that of the heat flux). A correct description of the mirror instability is given. The resonant interaction of three backward modes-fast acoustic, fast magnetosonic, and slow acoustic-under the conditions for the onset of the classical firehose instability triggers a new type of instability the growth rate of which is faster than the maximum growth rate of the conventional firehose instability. The results prove that, in contrast to the familiar Chew-Goldberger-Low approximate model, the anisotropic MHD approach provides a correct description of the large-scale dynamics of collisionless anisotropic plasmas (such as solar corona, solar wind, and ionospheric and magnetospheric plasmas).

  2. Theoretical modelling of the feedback stabilization of external MHD modes in toroidal geometry

    NASA Astrophysics Data System (ADS)

    Chance, M. S.; Chu, M. S.; Okabayashi, M.; Turnbull, A. D.

    2002-03-01

    A theoretical framework for understanding the feedback mechanism for stabilization of external MHD modes has been formulated. Efficient computational tools - the GATO stability code coupled with a substantially modified VACUUM code - have been developed to effectively design viable feedback systems against these modes. The analysis assumed a thin resistive shell and a feedback coil structure accurately modelled in θ and phi, albeit with only a single harmonic variation in phi. Time constants and induced currents in the enclosing resistive shell are calculated. An optimized configuration based on an idealized model has been computed for the DIII-D device. Up to 90% of the effectiveness of an ideal wall can be achieved.

  3. Computer Controlled MHD Power Consolidation and Pulse Generation System

    DTIC Science & Technology

    2007-11-02

    4465 Publication Date: Aug 01,1990 Title: Computer Controlled MHD Power Consolidation and Pulse Generation System Personal Author: Johnson, R...of Copies In Library: 000001 Record ID: 26725 : Computer Controlled MHD Power Consolidation and Pulse Generation System Final Technical Progress...Four-pulse CI System For A Diagonally Connected MHD Generator 14 9 Diagonal Output Voltage for Rsource =10 ohms, Rload = 1 ohm 16 10 Diagonal

  4. Advanced MHD Algorithm for Solar and Space Science: lst Year Semi Annual Progress Report

    NASA Technical Reports Server (NTRS)

    Schnack, Dalton D.; Lionello, Roberto

    2003-01-01

    We report progress for the development of MH4D for the first and second quarters of FY2004, December 29, 2002 - June 6, 2003. The present version of MH4D can now solve the full viscous and resistive MHD equations using either an explicit or a semi-implicit time advancement algorithm. In this report we describe progress in the following areas. During the two last quarters we have presented poster at the EGS-AGU-EUG Joint Assembly in Nice, France, April 6-11, 2003, and a poster at the 2003 International Sherwood Theory Conference in Corpus Christi, Texas, April 28-30 2003. In the area of code development, we have implemented the MHD equations and the semi-implicit algorithm. The new features have been tested.

  5. Structural organization and expression of amplified chromosomal sequences, which include the rudimentary gene, in cultured Drosophila cells resistant to N-(phosphonacetyl)-L-aspartate.

    PubMed

    Laval, M; Azou, Y; Miassod, R

    1989-12-01

    We have used 160 kilobases of cloned Drosophila genomic DNA from the rudimentary (r) region to examine the organization of amplified DNA in Drosophila cells resistant to 10 mM N-(phosphonacetyl)-L-aspartate (PALAr cells) obtained by stepwise selection. Evidence for the direct tandem linkage of the amplified sequences is presented. The pattern and intensity of amplified bands as well as the presence of novel junctions in the DNA sequence of PALAr cells indicate that there are two types of units of 150 and 120 kilobases long. The sequence of the smaller unit is entirely included within the larger one. The longer of the two units is present twice while the shorter one is amplified eightfold as compared to the level of the relevant DNA sequences in the wild-type. These data are consistent with a model in which successive crossing-over events over several cell cycles lead to amplification of the selected r gene and flanking sequences. However, these data can also be accounted for by a totally different mechanism in which multiple copies of DNA are generated by rolling circle replication. Transcription units other than the r gene are present within the 150 kilobase region of amplified DNA. These are found to be overexpressed in PALAr cells, though some transcripts are underrepresented relative to the copy number of the corresponding coding sequences.

  6. Effective method for MHD retrofit of power plants

    SciTech Connect

    Berry, G.F.; Dennis, C.B.; Johnson, T.R.; Minkov, V.

    1981-10-01

    Retrofitting existing power plants with an open-cycle MHD system has been re-examined in light of recent developments in the heat and seed recovery technology area. A new retrofit cycle configuration has been developed which provides for a direct gas-gas coupling; also, the MHD topping cycle can be decoupled from the existing plant for either separate or joint operation. As an example, the MHD retrofit concept has been applied to Illinois Power Company's Vermilion Station No. 1, a coal-fired power plant presently in operation. Substantial increases in efficiency have been demonstrated and the economic validity of the MHD retrofit approach has been established.

  7. EDITORIAL: Selected papers from the 16th Workshop on MHD Stability Control: Optimizing and Understanding the Role of Coils for Mode Control Selected papers from the 16th Workshop on MHD Stability Control: Optimizing and Understanding the Role of Coils for Mode Control

    NASA Astrophysics Data System (ADS)

    La Haye, Rob

    2012-09-01

    The Magnetohydrodynamic (MHD) Control Workshop with the theme 'Optimizing and Understanding the Role of Coils for Mode Control' was held at General Atomics (20-22 November 2011) following the 2011 APS-DPP Annual Meeting in Salt Lake City, Utah (14-18 November). This was the 16th in the annual series and was organized jointly by Columbia University, General Atomics, Princeton Plasma Physics Laboratory, and the University of Wisconsin-Madison. Program committee participation included representatives from the EU and Japan along with other US laboratory and university institutions. This workshop highlighted the role of applied non-axisymmetric magnetic fields from both internal and external coils for control of MHD stability to achieve high performance fusion plasmas. The application of 3D magnetic field offers control of important elements of equilibrium, stability, and transport. The use of active 3D fields to stabilize global instabilities and to correct magnetic field errors is an established tool for achieving high beta configurations. 3D fields also affect transport and plasma momentum, and are shown to be important for the control of edge localized modes (ELMs), resistive wall modes, and optimized stellarator configurations. The format was similar to previous workshops, including 13 invited talks, 21 contributed talks, and this year there were 2 panel discussions ('Error Field Correction' led by Andrew Cole of Columbia University and 'Application of Coils in General' led by Richard Buttery of General Atomics). Ted Strait of General Atomics also gave a summary of the International Tokamak Physics Activity (ITPA) MHD meeting in Padua, a group for which he is now the leader. In this special section of Plasma Physics and Controlled Fusion (PPCF) is a sample of the presentations at the workshop, which have been subject to the normal refereeing procedures of the journal. They include a review (A Boozer) and an invited talk (R Fitzpatrick) on error fields, an invited

  8. Analysis of Helicities and Hall and MHD Dynamo Effects in Two-Fluid Reversed-Field Pinch Simulations

    NASA Astrophysics Data System (ADS)

    Sauppe, Joshua; Sovinec, Carl

    2015-11-01

    Relaxation in the RFP is studied numerically with extended-MHD modeling that includes the Hall term and ion gyroviscous stress. Previous results show significant coupling between magnetic relaxation and parallel flow evolution [King PoP 19, 055905]. Computations presented here display quasi-periodic relaxation events with current relaxation through MHD and Hall dynamo drives. The MHD dynamo always relaxes currents while the Hall dynamo may add or subtract from it, but the total dynamo drive is similar to single-fluid MHD computations. Changes in plasma momentum are due to viscous coupling to the wall and fluctuation-induced Maxwell stresses transport momentum radially inward when two-fluid effects are included. The magnetic helicity and hybrid helicity, a two-fluid extension of magnetic helicity that includes cross and kinetic helicity [Turner, 1986], are well-conserved relative to magnetic energy at each event. The cross helicity is well-conserved in single-fluid MHD but is significantly affected by both two-fluid effects and ion gyroviscosity. The plasma parallel current evolves towards the predicted flat profile; however, the plasma flow does not. Work supported through NSF grant PHY-0821899 and DOE grant DE-FG02-06ER54850.

  9. MHD Integrated Topping Cycle Project. Thirteenth quarterly technical progress report, August 1, 1990--October 31, 1990

    SciTech Connect

    Not Available

    1992-01-01

    The overall objective of the project is to design and construct prototypical hardware for an integrated MHD topping cycle, and conduct long duration proof-of-concept tests of integrated system at the US DOE Component Development and Integration Facility in Butte, Montana. The results of the long duration tests will augment the existing engineering design data base on MHD power train reliability, availability, maintainability, and performance, and will serve as a basis for scaling up the topping cycle design to the next level of development, an early commercial scale power plant retrofit. The components of the MHD power train to be designed, fabricated, and tested include: A slagging coal combustor with a rated capacity of 50 MW thermal input, capable of operation with an Eastern (Illinois {number_sign}6) or Western (Montana Rosebud) coal, a segmented supersonic nozzle, a supersonic MHD channel capable of generating at least 1.5 MW of electrical power, a segmented supersonic diffuser section to interface the channel with existing facility quench and exhaust systems, a complete set of current control circuits for local diagonal current control along the channel, and a set of current consolidation circuits to interface the channel with the existing facility inverter.

  10. Multimegawatt nuclear electric propulsion with gaseous and vapor core reactors with MHD

    NASA Astrophysics Data System (ADS)

    Knight, Travis; Anghaie, Samim; Smith, Blair; Houts, Michael

    2001-02-01

    This study investigated the development of a system concept for space power generation and nuclear electric propulsion based on a fissioning plasma core reactor (FPCR) with magnetohydrodynamic (MHD) power conversion system, coupled to a magnetoplasmadynamic (MPD) thruster. The FPCR is a liquid-vapor core reactor concept operating with metallic uranium or uranium tetrafluoride (UF4) vapor as the fissioning fuel and alkali metals or their fluorides as working fluid in a closed Rankine cycle with MHD energy conversion. Candidate working fluids include K, Li, Na, KF, LiF, NaF, etc. The system features core outlet temperatures of 3000 to 4000 K at pressures of about 1 to 10 MPa, MHD temperatures of 2000 to 3000 K, and radiator temperatures of 1200 to 2000 K. This combination of parameters offers the potential for low total system specific mass in the range of 0.4 to 0.6 kg/kWe. The MHD output could be coupled with minimal power conditioning to the variable specific impulse magnetoplasma rocket (VASIMR), MPD thrusters or other types of thruster for producing thrust at very high specific impulse (Isp=1500 to 10,000 s). .

  11. On The Role of MHD Waves in Heating Localised Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Erdélyi, R.; Nelson, C. J.

    2016-04-01

    Satellite and ground-based observations from e.g. SOHO, TRACE, STEREO, Hinode, SDO and IRIS to DST/ROSA, IBIS, CoMP, STT/CRISP have provided a wealth of evidence of waves and oscillations present in a wide range of spatial scales of the magnetised solar atmosphere. Our understanding about localised solar structures has been considerably changed in light of these high spatial and time resolution observations. However, MHD waves not only enable us to perform sub-resolution magneto-seismology of magnetic waveguides but are also potential candidates to carry and damp the necessary non-thermal energy in these localised waveguides. First, we will briefly outline the basic recent developments in MHD wave theory focussing on linear waves. Next, we discuss the role of the most frequently studied wave classes, including the Alfven, and magneto-acoustic kink and sausage waves. The current theoretical (and often difficult) interpretations of the detected solar atmospheric wave and oscillatory phenomena within the framework of MHD will be shown. Last, the latest reported observational findings of potential MHD wave flux, in terms of localised plasma heating, in the solar atmosphere is discussed, bringing us closer to solve the coronal heating problem.

  12. Development of MHD Wave Diagnostic and Models of Coronal Active Regions

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Thompson, B. J.; Davila, J. M.

    2004-05-01

    We investigate the generation, propagation, and damping of MHD waves in active regions, with the goal to develop a diagnostic tool of active region structure, dynamics, and stability. We used 3D MHD model to study the generation and the propagation of EIT waves in a simple model of an active regions, and the interaction of EIT waves with the active region magnetic field. We model the oscillation of active region loops numerically using the 3D MHD model active regions. Such oscillations have been recently observed by TRACE. We use photospheric magnetograms as the boundary conditions for the magnetic field model, and construct an initial field using force-free extrapolation. Finite plasma temperature, density, and gravity are included in the model. We construct loop density structures in the model, guided by TRACE and EIT observations in the EUV. We demonstrate that by comparing the results of the MHD models of waves in an active region to observations we will be able to construct a diagnostic tool for the physical properties of the active regions, such as magnetic field and density structure.

  13. Multi-drug resistant E.coli urosepsis in physicians following transrectal ultrasound guided prostate biopsies--three cases including one death.

    PubMed

    Carlson, William H; Bell, David G; Lawen, Joseph G; Rendon, Ricardo A

    2010-04-01

    Three male physicians underwent transrectal ultrasound guided prostate biopsies for elevated prostate-specific antigen levels or irregular digital rectal exam findings. All three of these patients developed urosepsis secondary to multi-drug resistant organisms despite antibiotic prophylaxis. There are increasing reports of infectious complications following prostate biopsy caused by multi-drug resistant organisms. These cases highlight the potentially lethal risks to healthcare workers who are more likely to harbor multi-drug resistant organisms than the general population. Further research into preoperative assessment and appropriate antibiotic prophylaxis in all potentially high risk patients is warranted.

  14. Magnetohydrodynamic (MHD) driven droplet mixer

    DOEpatents

    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.

  15. Randomized comparison of renal denervation versus intensified pharmacotherapy including spironolactone in true-resistant hypertension: six-month results from the Prague-15 study.

    PubMed

    Rosa, Ján; Widimský, Petr; Toušek, Petr; Petrák, Ondřej; Čurila, Karol; Waldauf, Petr; Bednář, František; Zelinka, Tomáš; Holaj, Robert; Štrauch, Branislav; Šomlóová, Zuzana; Táborský, Miloš; Václavík, Jan; Kociánová, Eva; Branny, Marian; Nykl, Igor; Jiravský, Otakar; Widimský, Jiří

    2015-02-01

    This prospective, randomized, open-label multicenter trial evaluated the efficacy of catheter-based renal denervation (Symplicity, Medtronic) versus intensified pharmacological treatment including spironolactone (if tolerated) in patients with true-resistant hypertension. This was confirmed by 24-hour ambulatory blood pressure monitoring after excluding secondary hypertension and confirmation of adherence to therapy by measurement of plasma antihypertensive drug levels before enrollment. One-hundred six patients were randomized to renal denervation (n=52), or intensified pharmacological treatment (n=54) with baseline systolic blood pressure of 159±17 and 155±17 mm Hg and average number of drugs 5.1 and 5.4, respectively. A significant reduction in 24-hour average systolic blood pressure after 6 months (-8.6 [95% cofidence interval: -11.8, -5.3] mm Hg; P<0.001 in renal denervation versus -8.1 [95% cofidence interval: -12.7, -3.4] mm Hg; P=0.001 in pharmacological group) was observed, which was comparable in both groups. Similarly, a significant reduction in systolic office blood pressure (-12.4 [95% cofidence interval: -17.0, -7.8] mm Hg; P<0.001 in renal denervation versus -14.3 [95% cofidence interval: -19.7, -8.9] mm Hg; P<0.001 in pharmacological group) was present. Between-group differences in change were not significant. The average number of antihypertensive drugs used after 6 months was significantly higher in the pharmacological group (+0.3 drugs; P<0.001). A significant increase in serum creatinine and a parallel decrease of creatinine clearance were observed in the pharmacological group; between-group difference were borderline significant. The 6-month results of this study confirmed the safety of renal denervation. In conclusion, renal denervation achieved reduction of blood pressure comparable with intensified pharmacotherapy.

  16. Mercuric ion-resistance operons of plasmid R100 and transposon Tn501: the beginning of the operon including the regulatory region and the first two structural genes.

    PubMed Central

    Misra, T K; Brown, N L; Fritzinger, D C; Pridmore, R D; Barnes, W M; Haberstroh, L; Silver, S

    1984-01-01

    The mercuric ion-resistance operons of plasmid R100 (originally from Shigella) and transposon Tn501 (originally from a plasmid isolated in Pseudomonas) have been compared by DNA sequence analysis. The sequences for the first 1340 base pairs of Tn501 are given with the best alignment with the comparable 1319 base pairs of R100. The homology between the two sequences starts at base 58 after the end of the insertion sequence IS-1 of R100. The sequences include the transcriptional regulatory region, and the homology is particularly strong in regions just upstream from potential transcriptional initiation sites. The trans-acting regulatory gene merR consists of 180 base pairs in both cases and codes for a highly basic polypeptide of 60 amino acids, which is also rich in serine. The Tn501 and R100 merR genes differ in 25 of the 180 base positions, and the resulting polypeptides differ in seven amino acids. The regulatory region before the major transcription initiation site contains potential -35 and -10 sequences and dyad symmetrical sequences, which may be the merR binding sites for transcriptional regulation. The first structural gene, merT, encodes a highly hydrophobic polypeptide of 116 amino acids. The R100 and Tn501 merT genes differ in 17% of their positions, leading to 14 (12%) amino acid changes. This region had previously been shown to encode a protein governing membrane transport of mercuric ions. The second structural gene, merC, would give a 91 amino acid polypeptide with a hydrophobic amino-terminal segment. The Tn501 and R100 merC genes differ at 37 base positions, leading to 10 amino acid changes. PMID:6091128

  17. Drift-resistive-inertial ballooning modes in quasihelical stellarators

    SciTech Connect

    Rafiq, T.; Kritz, A. H.; Hegna, C. C.; Callen, J. D.

    2010-02-15

    A linear stability theory of nonideal magnetohydrodynamic (MHD) ballooning modes is investigated using a two fluid model for electron-ion plasmas. Drift-resistive-inertial ballooning mode eigenvalues and eigenfunctions are calculated for a variety of equilibria including axisymmetric shifted circular geometry (s-alpha model) as well as for three dimensional configurations relevant for the Helically Symmetric Stellarator (HSX) [F. S. B. Anderson, A. F. Almagri, D. T. Anderson, et al., Fusion Technology 27, 273 (1995)]. For typical HSX parameters, characteristic ballooning mode growth rates exceed the electron collision frequency. In this regime, electron inertial effects dominate plasma resistivity and produce an instability whose growth rate scales with the electromagnetic skin depth. However, as plasma beta is increased, the resistive and inertial effects become unimportant. Under these conditions, the mode is completely stabilized by drift frequency effects, which dominate resistivity and inertia. Numerical results indicate that in the absence of drift effects, the resistive-inertial MHD modes are purely growing and persist in regimes where ideal MHD ballooning modes are stable. It is found that the magnitudes of the linear growth rates are not sensitive to the addition of a mirror term to the magnetic spectrum that spoils the quasihelical symmetry of the configuration. The eigenvalues and eigenvectors in the strong ballooning approximation are used together with a quasilinear mixing length estimate to determine particle flux and particle diffusivity. The particle diffusivity increases with rising density gradient and collisionality in a plasma with a low electron temperature. This increase in transport is consistent with the increase observed in the edge region of HSX plasmas. The magnitude of the particle diffusivity is computed to be in the range from 5 to 10 m{sup 2}/s, which is consistent with the experimental measured particle diffusivity at the edge of HSX

  18. MHD Electrode and wall constructions

    DOEpatents

    Way, Stewart; Lempert, Joseph

    1984-01-01

    Electrode and wall constructions for the walls of a channel transmitting the hot plasma in a magnetohydrodynamic generator. The electrodes and walls are made of a plurality of similar modules which are spaced from one another along the channel. The electrodes can be metallic or ceramic, and each module includes one or more electrodes which are exposed to the plasma and a metallic cooling bar which is spaced from the plasma and which has passages through which a cooling fluid flows to remove heat transmitted from the electrode to the cooling bar. Each electrode module is spaced from and electrically insulated from each adjacent module while interconnected by the cooling fluid which serially flows among selected modules. A wall module includes an electrically insulating ceramic body exposed to the plasma and affixed, preferably by mechanical clips or by brazing, to a metallic cooling bar spaced from the plasma and having cooling fluid passages. Each wall module is, similar to the electrode modules, electrically insulated from the adjacent modules and serially interconnected to other modules by the cooling fluid.

  19. Nonlinear MHD Waves in a Prominence Foot

    NASA Astrophysics Data System (ADS)

    Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.

    2015-11-01

    We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ˜ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5-11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5-14 G. For the typical prominence density the corresponding fast magnetosonic speed is ˜20 km s-1, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.

  20. Annular MHD Physics for Turbojet Energy Bypass

    NASA Technical Reports Server (NTRS)

    Schneider, Steven J.

    2011-01-01

    The use of annular Hall type MHD generator/accelerator ducts for turbojet energy bypass is evaluated assuming weakly ionized flows obtained from pulsed nanosecond discharges. The equations for a 1-D, axisymmetric MHD generator/accelerator are derived and numerically integrated to determine the generator/accelerator performance characteristics. The concept offers a shockless means of interacting with high speed inlet flows and potentially offers variable inlet geometry performance without the complexity of moving parts simply by varying the generator loading parameter. The cycle analysis conducted iteratively with a spike inlet and turbojet flying at M = 7 at 30 km altitude is estimated to have a positive thrust per unit mass flow of 185 N-s/kg. The turbojet allowable combustor temperature is set at an aggressive 2200 deg K. The annular MHD Hall generator/accelerator is L = 3 m in length with a B(sub r) = 5 Tesla magnetic field and a conductivity of sigma = 5 mho/m for the generator and sigma= 1.0 mho/m for the accelerator. The calculated isentropic efficiency for the generator is eta(sub sg) = 84 percent at an enthalpy extraction ratio, eta(sub Ng) = 0.63. The calculated isentropic efficiency for the accelerator is eta(sub sa) = 81 percent at an enthalpy addition ratio, eta(sub Na) = 0.62. An assessment of the ionization fraction necessary to achieve a conductivity of sigma = 1.0 mho/m is n(sub e)/n = 1.90 X 10(exp -6), and for sigma = 5.0 mho/m is n(sub e)/n = 9.52 X 10(exp -6).

  1. MHD Turbulence at Moderate Magnetic Reynolds Number

    NASA Technical Reports Server (NTRS)

    Knaepen, B.; Kassinos, S.; Carati, D.

    2003-01-01

    In the present article we will consider the decay of MHD turbulence under the influence of a strong external magnetic field at moderate magnetic Reynolds numbers. Typical values of R(sub m) that are considered here range from R(sub m) approx. 0.1 to R(sub m) approx. 20. As a comparison, the initial kinetic Reynolds number common to all our simulations is Re(sub L) = 199. This means that the range of Prandtl numbers explored is 5 x 10(exp -4) to 10(exp -1). Our motivation is mainly to exhibit how the transition from the QS approximation to FMHD occurs. At the lowest values of R(sub m) studied here, the QS approximation is shown to model the flow faithfully. However, for the higher values of R(sub m) considered, it is clearly inadequate but can be replaced by another approximation which will be referred to as the Quasi-Linear (QL) approximation. Another objective of the present study is to describe how variations in the magnetic Reynolds number (while maintaining all other parameters constant) affect the dynamics of the flow. This complements past studies where variations in either the strength of the external magnetic field or the kinetic Reynolds number were considered. This article is organized as follows. In section 2 we recall the definition of the quasi-static approximation. Section 3 is devoted to the description of the numerical experiments performed using the quasi-static approximation and full MHD. In section 4 we describe the quasi-linear approximation and test it numerically against full MHD. A concluding summary is given in section 5.

  2. NONLINEAR MHD WAVES IN A PROMINENCE FOOT

    SciTech Connect

    Ofman, L.; Knizhnik, K.; Kucera, T.; Schmieder, B.

    2015-11-10

    We study nonlinear waves in a prominence foot using a 2.5D MHD model motivated by recent high-resolution observations with Hinode/Solar Optical Telescope in Ca ii emission of a prominence on 2012 October 10 showing highly dynamic small-scale motions in the prominence material. Observations of Hα intensities and of Doppler shifts show similar propagating fluctuations. However, the optically thick nature of the emission lines inhibits a unique quantitative interpretation in terms of density. Nevertheless, we find evidence of nonlinear wave activity in the prominence foot by examining the relative magnitude of the fluctuation intensity (δI/I ∼ δn/n). The waves are evident as significant density fluctuations that vary with height and apparently travel upward from the chromosphere into the prominence material with quasi-periodic fluctuations with a typical period in the range of 5–11 minutes and wavelengths <2000 km. Recent Doppler shift observations show the transverse displacement of the propagating waves. The magnetic field was measured with the THEMIS instrument and was found to be 5–14 G. For the typical prominence density the corresponding fast magnetosonic speed is ∼20 km s{sup −1}, in qualitative agreement with the propagation speed of the detected waves. The 2.5D MHD numerical model is constrained with the typical parameters of the prominence waves seen in observations. Our numerical results reproduce the nonlinear fast magnetosonic waves and provide strong support for the presence of these waves in the prominence foot. We also explore gravitational MHD oscillations of the heavy prominence foot material supported by dipped magnetic field structure.

  3. Detection of vancomycin-resistant enterococci from faecal samples of Iberian wolf and Iberian lynx, including Enterococcus faecium strains of CC17 and the new singleton ST573.

    PubMed

    Gonçalves, Alexandre; Igrejas, Gilberto; Radhouani, Hajer; López, María; Guerra, Ana; Petrucci-Fonseca, Francisco; Alcaide, Eva; Zorrilla, Irene; Serra, Rodrigo; Torres, Carmen; Poeta, Patrícia

    2011-12-01

    The aim of this study was to perform the molecular characterization of vancomycin resistant enterococci (VRE) within the faecal flora of Iberian wolf and Iberian lynx. The association with other resistance genes and the detection of virulence genes were also analysed. From 2008 to 2010, 365 faecal samples from Iberian wolf and Iberian lynx were collected and tested for VRE recovery. Mechanisms of resistance to vancomycin and other antibiotics, as well as genes encoding virulence factors were detected through PCR. Multilocus Sequence Typing (MLST) was performed for Enterococcus faecium strains. VRE were recovered in 8 of the 365 analysed samples. The vanA gene was identified in two E. faecium isolates recovered from Iberian wolf faecal samples and the remaining six showed intrinsic resistance (3 vanC1-E. gallinarum and 3 vanC2-E. casseliflavus, from Iberian wolf and Iberian lynx faecal samples, respectively). One vanA-containing isolate showed tetracycline and erythromycin resistance [with erm(B) and tet(L) genes] and the other one also exhibited ampicillin and kanamycin resistance [with erm(B), tet(M) and aph(3')-III genes]. One of the vanA-isolates revealed a new sequence type named ST573 and the other one belonged to the CC17 clonal complex (ST18). The hyl gene was detected in one E. casseliflavus and three E. gallinarum but not among vanA-positive isolates, and the occurrence of cylA and cylL genes was confirmed in two E. casseliflavus isolates. A low prevalence of VRE has been detected in faecal samples of Iberian wolf and Iberian lynx and strains with an acquired mechanism of resistance to vancomycin have not been detected among Iberian lynx.

  4. Stellarator expansion methods for MHD equilibrium and stability calculations

    SciTech Connect

    Lynch, V.E.; Charlton, L.A.; Hicks, H.R.; Holmes, J.A.; Carreras, B.A.; Hender, T.C.; Garcia, L.

    1986-03-01

    Two methods for performing stellarator expansion, or average method, MHD calculations are described. The first method includes the calculation of vacuum, equilibrium, and stability, using the Greene and Johnson stellarator expansion in which the equilibrium is reduced to a 2-D problem by averaging over the geometric toroidal angle in real space coordinates. In the second method, the average is performed in a system of vacuum magnetic coordinates. Both methods are implemented to utilize realistic vacuum field information, making them applicable to configuration studies and machine design, as well as to basic research. Illustrative examples are presented to detail the sensitivities of the calculations to physical parameters and to show numerical convergence and the comparison of these methods with each other and with other methods.

  5. V3FIT: Three-Dimensional MHD Equilibrium Reconstruction

    NASA Astrophysics Data System (ADS)

    Hanson, James D.; Shields, John; Hirshman, S. P.; Lazarus, E. A.; Lao, L.; Knowlton, S. F.

    2007-11-01

    V3FIT is a three-dimensional MHD equilibrium reconstruction code, based on the VMEC equilibrium code. V3FIT is a general and easily extensible reconstruction code, designed so that information from many types of diagnostics can be used to determine the equilibrium. The first diagnostics included in V3FIT were magnetic diagnostics. We will present results on reconstruction using microwave interferometers and polarimeters as diagnostics. We will also show comparisons between V3FIT and EFIT reconstructions using experimental data from the DIII-D tokamak. This work is supported in part by US DOE Grant DE-FG02-03ER54692B and a US DOE Postdoctoral Research Fellowship.

  6. Transpiration cooled electrodes and insulators for MHD generators

    DOEpatents

    Hoover, Jr., Delmer Q.

    1981-01-01

    Systems for cooling the inner duct walls in a magnetohydrodynamic (MHD) generator. The inner face components, adjacent the plasma, are formed of a porous material known as a transpiration material. Selected cooling gases are transpired through the duct walls, including electrically insulating and electrode segments, and into the plasma. A wide variety of structural materials and coolant gases at selected temperatures and pressures can be utilized and the gases can be drawn from the generation system compressor, the surrounding environment, and combustion and seed treatment products otherwise discharged, among many other sources. The conduits conducting the cooling gas are electrically insulated through low pressure bushings and connectors so as to electrically isolate the generator duct from the ground.

  7. Magnetogasdynamic Phenomena in Pulsed MHD Flows.

    DTIC Science & Technology

    1979-10-01

    r D-A079 919 STD RESEARCH CORP ARCADIA CALIF F/a 20/9 VA NETOGASDYNAMIC PHENODE’A IN PULSED MHD FLOWS.(U) OCT 79 D A OLIVER, T F SWEAN. D M MARKHAN...N00014-77-C-0574 UNCLASSIFIED STD -UP-002-77-1 NL ".’ rnunnnnunnnnSllflflflflflflf lllll /////IlEEEEE//!i *fl///////lfl l I/fflIEN I2) STD -UP-002-77-1...DEMETRIADES OCTOBER 1979 --A li JTlrSUMMARY REPORT FOR THE PERIOD 1 OCTOBER 1978 THROUGH 30 SEPTEMBER 1979 STD RESEARCH CORPORATION ARCADIA, CA S1006 PREPARED

  8. MHD oxidant intermediate temperature ceramic heater study

    NASA Technical Reports Server (NTRS)

    Carlson, A. W.; Chait, I. L.; Saari, D. P.; Marksberry, C. L.

    1981-01-01

    The use of three types of directly fired ceramic heaters for preheating oxygen enriched air to an intermediate temperature of 1144K was investigated. The three types of ceramic heaters are: (1) a fixed bed, periodic flow ceramic brick regenerative heater; (2) a ceramic pebble regenerative heater. The heater design, performance and operating characteristics under conditions in which the particulate matter is not solidified are evaluated. A comparison and overall evaluation of the three types of ceramic heaters and temperature range determination at which the particulate matter in the MHD exhaust gas is estimated to be a dry powder are presented.

  9. Results from conceptual design study of potential early commercial MHD/steam power plants

    NASA Technical Reports Server (NTRS)

    Hals, F.; Kessler, R.; Swallom, D.; Westra, L.; Zar, J.; Morgan, W.; Bozzuto, C.

    1981-01-01

    This paper presents conceptual design information for a potential early MHD power plant developed in the second phase of a joint study of such plants. Conceptual designs of plant components and equipment with performance, operational characteristics and costs are reported on. Plant economics and overall performance including full and part load operation are reviewed. Environmental aspects and the methods incorporated in plant design for emission control of sulfur and nitrogen oxides are reviewed. Results from reliability/availability analysis conducted are also included.

  10. MHD Integrated Topping Cycle Project

    NASA Astrophysics Data System (ADS)

    1993-04-01

    Manufacture, assembly, and checkout of combustion subsystem hardware was completed and the hardware was delivered to CDIF along with the water electrical isolators. A successful nozzle proof test was concluded; its purpose was to evaluate adequacy of the nozzle structure and sealing of sidewall-to-electrode wall joints, water tubes, and stud and wire penetrations at operating pressure. Design modifications to spare channel inlet frame were made to enable iron oxide injection. Results of tests in the CDIF 1A1 channel which compared effect of different cathode wall iron oxide injection locations indicated that injection through the side port may be more effective, particularly if one of the two ports becomes clogged. Design confirmation testing of a pneumatically driven ram to clear a plugged iron oxide injector tip was performed. Manufacture of spare and replacement parts for 1A4 channel and diffuser was begun. Construction of the cathode power cabinets and associated control system was completed. Hot-fire checkout series was completed for the combustion subsystem; 16.8 thermal hours were accumulated during seven tests. This test series demonstrated adequacy of overall cooling of combustion subsystem and provided an initial evaluation of heat losses and slagging characteristics. Several major facility activities at the CDIF were accomplished including installation and testing of new iron oxide pumps, initial on-line checkout of coal feed system modifications, modification of seed system including replacement of silo rotary feeder, installation of new filter receiver on the silo, conversion of fly ash bin to dust collector, removal of all of the electrical wiring (used for 1A1 channel) between the channel and HVR in order to install 1A4 wiring, and installation of the 1A4 channel.

  11. Movement of IS26-associated antibiotic resistance genes occurs via a translocatable unit that includes a single IS26 and preferentially inserts adjacent to another IS26.

    PubMed

    Harmer, Christopher J; Moran, Robert A; Hall, Ruth M

    2014-10-07

    The insertion sequence IS26 plays a key role in disseminating antibiotic resistance genes in Gram-negative bacteria, forming regions containing more than one antibiotic resistance gene that are flanked by and interspersed with copies of IS26. A model presented for a second mode of IS26 movement that explains the structure of these regions involves a translocatable unit consisting of a unique DNA segment carrying an antibiotic resistance (or other) gene and a single IS copy. Structures resembling class I transposons are generated via RecA-independent incorporation of a translocatable unit next to a second IS26 such that the ISs are in direct orientation. Repeating this process would lead to arrays of resistance genes with directly oriented copies of IS26 at each end and between each unique segment. This model requires that IS26 recognizes another IS26 as a target, and in transposition experiments, the frequency of cointegrate formation was 60-fold higher when the target plasmid contained IS26. This reaction was conservative, with no additional IS26 or target site duplication generated, and orientation specific as the IS26s in the cointegrates were always in the same orientation. Consequently, the cointegrates were identical to those formed via the known mode of IS26 movement when a target IS26 was not present. Intact transposase genes in both IS26s were required for high-frequency cointegrate formation as inactivation of either one reduced the frequency 30-fold. However, the IS26 target specificity was retained. Conversion of each residue in the DDE motif of the Tnp26 transposase also reduced the cointegration frequency. Importance: Resistance to antibiotics belonging to several of the different classes used to treat infections is a critical problem. Multiply antibiotic-resistant bacteria usually carry large regions containing several antibiotic resistance genes, and in Gram-negative bacteria, IS26 is often seen in these clusters. A model to explain the unusual

  12. Emerging importance of mismatch repair components including UvrD helicase and their cross-talk with the development of drug resistance in malaria parasite.

    PubMed

    Ahmad, Moaz; Tuteja, Renu

    2014-12-01

    Human malaria is an important parasitic infection responsible for a significant number of deaths worldwide, particularly in tropical and subtropical regions. The recent scenario has worsened mainly because of the emergence of drug-resistant malaria parasites having the potential to spread across the world. Drug-resistant parasites possess a defective mismatch repair (MMR); therefore, it is essential to explore its mechanism in detail to determine the underlying cause. Recently, artemisinin-resistant parasites have been reported to exhibit nonsynonymous single nucleotide polymorphisms in genes involved in MMR pathways such as MutL homolog (MLH) and UvrD. Plasmodium falciparum MLH is an endonuclease required to restore the defective MMR in drug-resistant W2 strain of P. falciparum. Although the role of helicases in eukaryotic MMR has been questioned, the identification and characterization of the UvrD helicase and their cross-talk with MLH in P. falciparum suggests the possible involvement of UvrD in MMR. A comparative genome-wide analysis revealed the presence of the UvrD helicase in Plasmodium species, while it is absent in human host. Therefore, PfUvrD may emerge as a suitable drug target to control malaria. This review study is focused on recent developments in MMR biochemistry, emerging importance of the UvrD helicase, possibility of its involvement in MMR and the emerging cross-talk between MMR components and drug resistance in malaria parasite.

  13. Incidence, Antimicrobial Resistance, and Molecular Characteristics of Nontyphoidal Salmonella Including Extended-Spectrum β-Lactamase Producers in Retail Chicken Meat.

    PubMed

    Choi, Dasom; Chon, Jung-Whan; Kim, Hong-Seok; Kim, Dong-Hyeon; Lim, Jong-Soo; Yim, Jin-Hyeok; Seo, Kun-Ho

    2015-11-01

    The present study was undertaken to determine the prevalence of Salmonella in 100 chicken carcass samples from five integrated broiler operation brands in Korea. Serotypes, antibiotic resistance patterns, extended-spectrum β-lactamase (ESBL) genotype, and clonal divergence using multilocus sequence typing of the isolated strains were analyzed. A total of 42 chicken samples were contaminated with nontyphoidal Salmonella (NTS) isolates: 16 isolates (38%) were Salmonella Virchow, 9 (21%) were Salmonella Bareilly, and 8 (19%) were Salmonella Infantis. A multidrug resistance (MDR; resistant to more than three classes of antibiotics) phenotype was observed in 29% of the isolates, which were resistant to five or more classes of antibiotics. The dominant MDR type was resistance to classes of penicillin, cephalosporins, aminoglycosides, quinolones, and tetracyclines. All the MDR isolates were positive for ESBL producers, and all but one (with the CTX-M-1 genotype) had the CTX-M-15 genotype. Multilocus sequence typing of the isolates revealed ST16 as the dominant sequence type; Salmonella Virchow, Salmonella Infantis, and Salmonella Richmond were all ST16, indicating a close genetic relationship between these serovars. This is the first study in Korea showing the CTX-M-1 type of NTS and the prevalence of ESBL-producing strains among NTS isolated from retail chicken meat. Our findings suggest that MDR Salmonella contamination is widely prevalent in retail chicken meat, and consumption of inadequately cooked products could lead to dissemination of NTS, which is hazardous to human health.

  14. Nonlinear tearing mode study using the almost ideal magnetohydrodynamics (MHD) constraint

    SciTech Connect

    Ren, C.; Callen, J.D.; Jensen, T.H.

    1998-12-31

    The tearing mode is an important resistive magnetohydrodynamics (MHD) mode. It perturbs the initial equilibrium magnetic flux surfaces through magnetic field line reconnection to form new flux surfaces with magnetic islands. In the study of the tearing mode, usually the initial equilibria are one dimensional with two ignorable coordinates and the perturbed equilibria are two dimensional with one ignorable coordinate. The tearing mode can be linearly unstable and its growth saturates at a fine amplitude. The neoclassical tearing mode theory shows that the mode can be nonlinearly driven by the bootstrap current even when it is linearly stable to the classical tearing mode. It is important to study the nonlinear behavior of the tearing mode. As an intrinsically nonlinear approach, the use of the almost ideal MHD constraint is suited to study the nonlinear properties of the tearing mode. In this paper, as a validation of the method, the authors study two characteristics of the tearing mode using the almost ideal MHD constraint: (1) the linear stability condition for the initial one dimensional equilibrium; and (2) the final saturation level for the unstable case. In this work, they only consider the simplest case where no gradient of pressure or current density exists at the mode resonant surface.

  15. MHD shocks in the ISM

    NASA Technical Reports Server (NTRS)

    Chernoff, D. F.; Hollenbach, David J.; Mckee, Christopher F.

    1990-01-01

    Researchers survey shock solutions of a partially ionized gas with a magnetic field. The gas is modeled by interacting neutral, ion, electron and charged grain components. They employ a small neutral-ion chemical network to follow the dissociation and ionization of the major species. Cooling by molecular hydrogen (rotational, vibrational and dissociation), grains and dipole molecules is included. There are three basic types of solutions (C, C asterisk, and J) and some more complicated flows involving combinations of the basic types. The initial preshock conditions cover hydrogen nuclei densities of 1 less than n less than 10(exp 10) cm(-3) and shock velocities of 5 less than v(sub s) less than 60 km/s. The magnetic field is varied over 5 decades and the sensitivity of the results to grain parameters, UV and cosmic ray fluxes is ascertained. The parameter space is quite complicated, but there exist some simple divisions. When the initial ionization fraction is small (chi sub i less than 10(-5)), there is a sharp transition between fully C solutions at low velocity and strong J solutions at high velocity. When the initial ionization fraction is larger, C asterisk and/or very weak J shocks are present at low velocities in addition to the C solutions. The flow again changes to strong J shocks at high velocities. When the ionization fraction is large and the flow is only slightly greater than the bulk Alfven velocity, there is a complicated mixture of C, C asterisk and J solutions.

  16. Effect of fast electrons on the stability of resistive interchange modes in the TJ-II stellarator

    NASA Astrophysics Data System (ADS)

    García, L.; Ochando, M. A.; Carreras, B. A.; Carralero, D.; Hidalgo, C.; van Milligen, B. Ph.

    2016-06-01

    In this paper, we report on electromagnetic phenomena in low-β plasmas at the TJ-II stellarator, controlled by external heating. To understand the observations qualitatively, we introduce a simple modification of the standard resistive MHD equations, to include the potential impact of fast electrons on instabilities. The dominant instabilities of the modeling regime are resistive interchange modes, and calculations are performed in a configuration with similar characteristics as the TJ-II stellarator. The main effect of the trapping of fast electrons by magnetic islands induced by MHD instabilities is to increase the magnetic component of the fluctuations, changing the character of the instability to tearing-like and modifying the frequency of the modes. These effects seem to be consistent with some of the experimental observations.

  17. Effect of intradialytic resistance band exercise on physical function in patients on maintenance hemodialysis: a pilot study.

    PubMed

    Bullani, Roberto; El-Housseini, Youssef; Giordano, Fabrice; Larcinese, Anna; Ciutto, Lorella; Bertrand, Pauline Coti; Wuerzner, Grégoire; Burnier, Michel; Teta, Daniel

    2011-01-01

    Although physical activity is recommended in patients on maintenance hemodialysis (MHD), randomized controlled trials testing the effects of exercise in this population have given conflicting results. In general, aerobic exercises mostly failed to produce improvements in physical function, whereas resistance exercises, although less studied, appeared to be more promising. The use of sophisticated materials such as leg press and free weights may preclude widespread application of resistance training in patients on MHD. Simple and cheap elastic bands may thus be an attractive alternative. We tested the feasibility of a supervised intradialytic resistance band exercise training program, and its effects on physical function, in patients on MHD. A total of 11 unselected adult patients on MHD from our center, aged 70 ± 10.7 (mean ± standard deviation) years, including 8 men and 3 women, accepted to follow the program under the supervision of qualified physiotherapists. Thirty-six exercise sessions of moderate intensity (twice a week, mean duration 40 minutes each, during 4.5 to 6 months), mainly involving leg muscles against an elastic resistance, were performed. The exercise program was well tolerated and all patients completed it. Statistically significant improvements were observed in the following tests: Tinetti test, 23.9 ± 3.9 points before versus 25.7 ± 3.5 points after the program (P = .022); the Timed Up and Go test, 12.1 ± 6.6 versus 10 ± 5.8 seconds (P = .0156). Improvements in the 6-minute walk distance and in the one-leg balance tests just failed to reach statistical significance. In this single-center pilot study, an intradialytic resistance band exercise program was feasible, well tolerated, and showed encouraging results on physical function.

  18. International Conference on MHD Electrical Power Generation, 7th, Massachusetts Institute of Technology, Cambridge, MA, June 16-20, 1980, Proceedings. Volumes 1, 2 & 3

    NASA Astrophysics Data System (ADS)

    Dawson, A. M.; Overlan, D.

    The first volume of this conference on magnetohydrodynamics (MHD) for electrical power generation covers: (1) MHD pilot plants; (2) MHD generator experiments and modeling; (3) the performance of various MHD generator types; (4) MHD channel design considerations; (5) MHD channel materials considerations; (6) MHD system components, heat recovery and emissions; and (7) MHD oxidizers and inverters. The second volume deals with (8) MHD system magnets and combustors; (9) MHD field, flow and chemical processes; (10) MHD fluid dynamics; (11) MHD electrical power plant design; (12) current transfer and diagnostics; and (13) MHD power plant systems considerations.

  19. The RFP dynamo: MHD to kinetic regimes

    NASA Astrophysics Data System (ADS)

    Sarff, J. S.; Almagri, A. F.; den Hartog, D. J.; McCollam, K. J.; Nornberg, M. D.; Sauppe, J. P.; Sovinec, C. R.; Terry, P. W.; Triana, J. C.; Brower, D. L.; Ding, W. X.; Parke, E.

    2015-11-01

    The hallmark of magnetic relaxation in an RFP plasma is profile flattening of J0 .B0 /B2 effected by a dynamo-like emf in Ohm's law. This is well-studied in single-fluid MHD, but recent MST results and extended MHD modeling show that both and the Hall emf, - /ene , are important, revealing decoupled electron and ion motion. Since dynamo is current-related, the electron fluid emf, , captures both effects. In MST, the electron flow is dominantly Ve , 1 ~E1 ×B0 /B2 , implying ~ / B . This and the Hall emf are measured in MST for comparison in Ohm's law. A finite-pressure response is also possible, e.g., ``diamagnetic dynamo'', ∇ . /ene , associated with diamagnetic drift, and ``kinetic dynamo'' associated with collisionless streaming of electrons in a stochastic magnetic field. Correlation measurements and using FIR interferometry and Thomson scattering reveal these as small but finite in MST. A kinetic emf might be expected for any high-beta plasma with inhomogeneous pressure. Support by DOE/NSF.

  20. 3D Hall MHD Reconnection Dynamics

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Rudakov, L.

    2002-05-01

    A 3D Hall MHD simulation code (VooDoo) has recently been developed at the Naval Research Laboratory. We present preliminary results of a fully 3D magnetic reconnection study using this code. The initial configuration of the plasma system is as follows. The ambient, reversed magnetic field is in the x-direction and is proportional to B0 tanh(y/Ly) where Ly is the scale length of the current sheet. Perturbation fields δ Bx and δ By are introduced to initiate the reconnection process. This initial configuration is similar to that used in the 2D GEM reconnection study. However, the perturbation fields are localized in the z-direction. We consider two cases: no guide field (Bz = 0) and a weak guide field (Bz = 0.1B0). We find that the reconnection process is not stationary in the z-direction but propagates in the B x ∇ n direction consistent with Hall drift physics. Hence, an asymmetric disruption of the current sheet ensues. The flow structure of the plasma in the vicinity of the X-point is complex. We find that the `neutral line' (i.e, along the z-direction) is not an ignorable coordinate and is not periodic in Hall MHD reconnection dynamics; two assumptions that are often made in reconnection studies. \\ Research supported by NASA and ONR

  1. Solar wind turbulence: Observations of MHD effects

    NASA Technical Reports Server (NTRS)

    Bavassano, B.

    1995-01-01

    Since the first in-situ observations it was realized that the solar wind is permeated by large-amplitude variations on a very extended range of scales. In this paper an overview of our present state of knowledge for fluctuations in the magnetohydrodynamic (MHD) regime is given. These fluctuations are an important component of the solar wind variability and notably contribute to the overall energy and momentum flux. They generally have a turbulent character and their amplitude is large enough to suggest the presence of nonlinear effects. In recent years the use of high time-resolution data on an extended range of heliocentric distances has allowed major steps towards a satisfactory understanding of the solar wind MHD fluctuations. Their radial evolution in the expanding wind has been determined through detailed analyses of the variations in their spectral features. correlations. and anisotropics. The role of interplanetary sources has been carefully investigated. The influence of interactions with structures convected by the solar wind has been examined. Fluctuations have been studied in the light of theories developed to draw together the effects of both incompressibility and compressibility. Increasing attention has been devoted to the intermittent character of the turbulence. Finally, very recent observations by Ulysses at high heliographic latitudes have allowed the first in-situ analysis of turbulence features in polar regions of the heliosphere.

  2. Singular Currents Near Magnetic Islands in MHD Equilibria: Effects of Pressure Variation Within Flux Surfaces and of Symmetry

    NASA Astrophysics Data System (ADS)

    Reiman, Allan

    2016-10-01

    We present an analytic calculation of the MHD equilibrium current near a magnetic island that includes the effect of the pressure variation on the flux surfaces in that region. The current has logarithmic singularities at the X-lines of magnetic islands in non-stellarator-symmetric equilibria. The singular components vanish in stellarator-symmetric MHD equilibria. (Equilibria invariant under combined reflection in the poloidal and toroidal angles. Tokamaks with balanced double-null divertors are stellarator symmetric, but single-null tokamaks are not.) These equilibrium solutions are to be contrasted with equilibria having B . ∇p = 0 , where the singular components of the pressure-driven currents vanish regardless of the symmetry. They are also to be contrasted with 3D MHD equilibrium solutions that have simply nested flux surfaces, where the pressure-driven current goes like 1 / x near rational surfaces, where x is the distance from the rational surface. (Except in the case of quasi-symmetric flux surfaces.) We work with a closed subset of the MHD equilibrium equations that involves only perpendicular force balance, and is decoupled from parallel force balance. It is not correct to use the parallel component of the conventional MHD force balance equation, B . ∇p = 0 , near magnetic islands. DOE contract DEAC02-76CH03073.

  3. Sub-Alfvénic reduced full-f Kinetic MHD equations to study flute like instabilities

    NASA Astrophysics Data System (ADS)

    Sengupta, W.; Hassam, A.; Antonsen, T. M., Jr.

    2016-10-01

    We develop a set of reduced sub-Alfvénic fluid as well as kinetic MHD equations which are suitable for studying flute like instabilities in MHD ordering. The full-f kinetic equations are obtained by reducing Kulsrud's complete set of kinetic MHD system and includes trapped ion dynamics in a toroidal geometry. The nonlinear equations show the presence of Mercier modes, electromagnetic effects, GAMs and Rosenbluth-Hinton zero frequency zonal flows. Linear stability based on our equations shall be compared to the well known Kruskal-Oberman Kinetic MHD stability criteria. In the supersonic limit, for large q, our system can be shown to be equivalent to CGL double adiabatic theory. In the marginal stability limit, we shall discuss trapped particle stabilization of interchange modes. Comparison will also be made to the sub-Alfvénic reduced MHD fluid equations in a large aspect ratio tokamak. We shall show that the trapped particle effects in kinetic theory can be treated as a boundary layer of width the square root of the inverse aspect ratio in phase space. Work supported by DOE.

  4. C-5-Modified Tetrahydropyrano-Tetrahydofuran-Derived Protease Inhibitors (PIs) Exert Potent Inhibition of the Replication of HIV-1 Variants Highly Resistant to Various PIs, including Darunavir

    PubMed Central

    Aoki, Manabu; Hayashi, Hironori; Yedidi, Ravikiran S.; Martyr, Cuthbert D.; Takamatsu, Yuki; Aoki-Ogata, Hiromi; Nakamura, Teruya; Nakata, Hirotomo; Das, Debananda; Yamagata, Yuriko; Ghosh, Arun K.

    2015-01-01

    ABSTRACT We identified three nonpeptidic HIV-1 protease inhibitors (PIs), GRL-015, -085, and -097, containing tetrahydropyrano-tetrahydrofuran (Tp-THF) with a C-5 hydroxyl. The three compounds were potent against a wild-type laboratory HIV-1 strain (HIV-1WT), with 50% effective concentrations (EC50s) of 3.0 to 49 nM, and exhibited minimal cytotoxicity, with 50% cytotoxic concentrations (CC50) for GRL-015, -085, and -097 of 80, >100, and >100 μM, respectively. All the three compounds potently inhibited the replication of highly PI-resistant HIV-1 variants selected with each of the currently available PIs and recombinant clinical HIV-1 isolates obtained from patients harboring multidrug-resistant HIV-1 variants (HIVMDR). Importantly, darunavir (DRV) was >1,000 times less active against a highly DRV-resistant HIV-1 variant (HIV-1DRVRP51); the three compounds remained active against HIV-1DRVRP51 with only a 6.8- to 68-fold reduction. Moreover, the emergence of HIV-1 variants resistant to the three compounds was considerably delayed compared to the case of DRV. In particular, HIV-1 variants resistant to GRL-085 and -097 did not emerge even when two different highly DRV-resistant HIV-1 variants were used as a starting population. In the structural analyses, Tp-THF of GRL-015, -085, and -097 showed strong hydrogen bond interactions with the backbone atoms of active-site amino acid residues (Asp29 and Asp30) of HIV-1 protease. A strong hydrogen bonding formation between the hydroxyl moiety of Tp-THF and a carbonyl oxygen atom of Gly48 was newly identified. The present findings indicate that the three compounds warrant further study as possible therapeutic agents for treating individuals harboring wild-type HIV and/or HIVMDR. IMPORTANCE Darunavir (DRV) inhibits the replication of most existing multidrug-resistant HIV-1 strains and has a high genetic barrier. However, the emergence of highly DRV-resistant HIV-1 strains (HIVDRVR) has recently been observed in vivo and in

  5. Synthesis and antimicrobial activity of small cationic amphipathic aminobenzamide marine natural product mimics and evaluation of relevance against clinical isolates including ESBL-CARBA producing multi-resistant bacteria.

    PubMed

    Igumnova, Elizaveta M; Mishchenko, Ekaterina; Haug, Tor; Blencke, Hans-Matti; Sollid, Johanna U Ericson; Fredheim, Elizabeth G Aarag; Lauksund, Silje; Stensvåg, Klara; Strøm, Morten B

    2016-11-15

    A library of small aminobenzamide derivatives was synthesised to explore a cationic amphipathic motif found in marine natural antimicrobials. The most potent compound E23 displayed minimal inhibitory concentrations (MICs) of 0.5-2μg/ml against several Gram-positive bacterial strains, including methicillin resistant Staphylococcus epidermidis (MRSE).E23 was also potent against 275 clinical isolates including Staphylococcus aureus, Enterococcus spp., Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae, as well as methicillin-resistant S. aureus (MRSA), vancomycin-resistant enterococci (VRE), and ESBL-CARBA producing multi-resistant Gram-negative bacteria. The study demonstrates how structural motifs found in marine natural antimicrobials can be a valuable source for making novel antimicrobial lead-compounds.

  6. Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics – Revisiting Perturbative Hybrid Kinetic-MHD Theory

    PubMed Central

    Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

    2016-01-01

    It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle’s Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas. PMID:27160346

  7. Flow-Induced New Channels of Energy Exchange in Multi-Scale Plasma Dynamics - Revisiting Perturbative Hybrid Kinetic-MHD Theory.

    PubMed

    Shiraishi, Junya; Miyato, Naoaki; Matsunaga, Go

    2016-05-10

    It is found that new channels of energy exchange between macro- and microscopic dynamics exist in plasmas. They are induced by macroscopic plasma flow. This finding is based on the kinetic-magnetohydrodynamic (MHD) theory, which analyses interaction between macroscopic (MHD-scale) motion and microscopic (particle-scale) dynamics. The kinetic-MHD theory is extended to include effects of macroscopic plasma flow self-consistently. The extension is realised by generalising an energy exchange term due to wave-particle resonance, denoted by δ WK. The first extension is generalisation of the particle's Lagrangian, and the second one stems from modification to the particle distribution function due to flow. These extensions lead to a generalised expression of δ WK, which affects the MHD stability of plasmas.

  8. MHD seawater thruster performance: A comparison of predictions with experimental results from a two Tesla test facility

    SciTech Connect

    Picologlou, B.F.; Doss, E.D.; Geyer, H.K. ); Sikes, W.C.; Ranellone, R.F. )

    1992-01-01

    A two Tesla test facility was designed, built, and operated to investigate the performance of magnetohydrodynamic (MHD) seawater thrusters. The results of this investigation are used to validate a design oriented MHD thruster performance computer code. The thruster performance code consists of a one-dimensional MHD hydrodynamic model coupled to a two-dimensional electrical model. The code includes major loss mechanisms affecting the performance of the thruster. Among these losses are the joule dissipation losses, frictional losses, electrical end losses, and single electrode potential losses. The facility test loop, its components, and their design are presented in detail. Additionally, the test matrix and its rationale are discussed. Representative experimental results of the test program are presented, and are compared to pretest computer model predictions. Good agreement between predicted and measured data has served to validate the thruster performance computer models.

  9. Design and calculated performance and cost of the ECAS Phase II open cycle MHD power generation system

    NASA Technical Reports Server (NTRS)

    Harris, L. P.

    1977-01-01

    A 2000 MWe MHD/steam plant for central station applications has been designed and costed as part of the Energy Conversion Alternatives Study (ECAS). This plant is fueled by Illinois No. 6 coal, rejects heat through mechanical draft wet cooling towers, and includes coal processing equipment, seed reprocessing, electrical inversion of the MHD generator output and emission controls to current EPA standards. It yields an estimated overall efficiency of 0.483 (7066 Btu/kWe-hr), a capital cost of $718 per kWe (1975 dollars), and a cost of electricity at 65% capacity factor of 32 mills per kWe-hr. If the assumed life and reliability could be achieved with these performance parameters, the MHD system should prove attractive.

  10. Synergistic interactions in two-drug and three-drug combinations (thymol, EDTA and vancomycin) against multi drug resistant bacteria including E. coli.

    PubMed

    Hamoud, Razan; Zimmermann, Stefan; Reichling, Jürgen; Wink, Michael

    2014-03-15

    Combinations of two or more drugs, which affect different targets, have frequently been used as a new approach against resistant bacteria. In our work we studied the antimicrobial activity (MIC, MBC) of individual drugs (the phenolic monoterpene thymol, EDTA and vancomycin), of two-drug interactions between thymol and EDTA in comparison with three-drug interactions with vancomycin against sensitive and resistant bacteria. Thymol demonstrated moderate bactericidal activity (MBC between 60 and 4000μg/ml) while EDTA only exhibited bacteriostatic activity over a range of 60-4000μg/ml. MICs of vancomycin were between 0.125 and 16μg/ml against Gram-positive and between 32 and 128μg/ml against Gram-negative bacteria. Checkerboard dilution and time-kill curve assays were performed to evaluate the mode of interaction of several combinations against Methicillin-resistant Staphylococcus aureus (MRSA NCTC 10442) and Escherichia coli (ATCC 25922). Checkerboard data indicate indifferent interaction against Gram-positive (FICI=1-1.3) and synergy against Gram-negative bacteria (FICI≈0.4), while time kill analyses suggest synergistic effect in different combinations against both types of bacteria. It is remarkable that the combinations could enhance the sensitivity of E. coli to vancomycin 16-fold to which it is normally insensitive. We have provided proof for the concept, that combinations of known antibiotics with modern phytotherapeutics can expand the spectrum of useful therapeutics.

  11. Antibiotic Resistance Pattern and Evaluation of Metallo-Beta Lactamase Genes Including bla- IMP and bla- VIM Types in Pseudomonas aeruginosa Isolated from Patients in Tehran Hospitals.

    PubMed

    Aghamiri, Samira; Amirmozafari, Nour; Fallah Mehrabadi, Jalil; Fouladtan, Babak; Samadi Kafil, Hossein

    2014-01-01

    Beta-lactamase producing strains of Pseudomonas aeruginosa are important etiological agents of hospital infections. Carbapenems are among the most effective antibiotics used against Pseudomonas infections, but they can be rendered infective by group B β -lactamase, commonly called metallo-beta lactamase. In this study, the antimicrobial sensitivity patterns of P. aeruginosa strains isolated from 9 different hospitals in Tehran, Iran, as well as the prevalence of MBLs genes (bla- VIM and bla- IMP ) were determined. A total of 212 strains of P. aeruginosa recovered from patients in hospitals in Tehran were confirmed by both biochemical methods and PCR. Their antimicrobial sensitivity patterns were determined by Kirby-Bauer disk diffusion method. Following MIC determination, imipenem resistant strains were selected by DDST method which was followed by PCR tests for determination of MBLs genes: bla- IMP and bla- VIM . The results indicated that, in the DDST phenotypic method, among the 100 imipenem resistant isolates, 75 strains were MBLs positive. The PCR test indicated that 70 strains (33%) carried bla- VIM gene and 20 strains (9%) harbored bla- IMP . The results indicated that the extent of antibiotic resistance among Pseudomonas aeruginosa is on the rise. This may be due to production of MBLs enzymes. Therefore, determination of antibiotic sensitivity patterns and MBLs production by these bacteria, can be important in control of clinical Pseudomonas infection.

  12. Development of multidrug resistance due to multiple factors including P-glycoprotein overexpression under K-selection after MYC and HRAS oncogene activation.

    PubMed

    Nakamura, Yukari; Sato, Hiroyuki; Motokura, Toru

    2006-05-15

    Multistep tumorigenesis is a form of microevolution consisting of mutation and selection. To clarify the role of selection modalities in tumor development, we examined two alternative evolutionary conditions, r-selection in sparse culture, which allows cells to proliferate rapidly, and K-selection in confluent culture, in which overcrowding constrains cell proliferation. Using MYC- and EJ-RAS-transformed rat embryo fibroblasts, we found that K-selected cells acquired and stably maintained multidrug resistance (MDR) to DOX, VCR, MTX and Ara-C. Then, we examined the involvement of a number of factors potentially causal of the development of MDR, that is, ploidy, Tp53 mutation, doubling time and the expression levels of genes related to drug resistance. Although ploidy status and Tp53 mutations did not correlate with MDR, we found that Abcb1/Mdr1, encoding P-glycoprotein (Pgp), was significantly upregulated after K-selection. Cyclosporin A, a competitive inhibitor of Pgp, increased the intracellular accumulation of DOX and reduced the resistance to it. Indeed, the population of Pgp-transfected cells significantly expanded under K-, but not under r-selection. In addition to Pgp upregulation, altered expression of other genes such as Cda/cytidine deaminase and Slc29a1/equilibrative nucleoside transporter 1 and prolonged doubling times were associated with MDR. This system reproduces events associated with MDR in vivo and would be useful for analysis of MDR development.

  13. MHD Augmentation of Rocket Engines Using Beamed Energy

    NASA Astrophysics Data System (ADS)

    Lineberry, John T.; Chapman, James N.; Litchford, Ron J.; Jones, Jonathan

    2003-05-01

    MHD technology and fundamental relations that pertain to accelerating a working fluid for propulsion of space vehicles are reviewed. Previous concepts on MHD propulsion have considered use of an on-board power supply to provide the electric power for the MHD thruster which is accompanied by an obvious weight penalty. In this study, an orbiting power station that beams microwave or laser power to the spacecraft is considered which eliminates this penalty making the thruster significantly more effective from the thrust-to-weight viewpoint. The objective of the study was to investigate augmenting a rocket motor to increase the ISP into the 2,500 seconds range using MHD acceleration. Mission scenarios are presented to parametrically compare the MHD augmented motor. Accelerator performance is calculated for an array of cases which vary the mass throughput, magnetic field strength and MHD interaction level. Performance improved with size, magnetic field strength and interaction level, although lower interaction levels can also produce attractive configurations. Accelerator efficiencies are typically 80-90%. The results display a large regime for improved performance in which the extent of the regime is critically dependent upon the weight of the power receiving equipment (rectenna). It is concluded that this system has potential when used with an orbiting power station that transmits power to the space vehicle by microwave radiation or laser beams. The most critical technology improvement needed is a reduced weight rectenna system but more development is also needed on the MHD accelerator, which is currently underway with NASA sponsorship.

  14. Revisiting MHD stability comparison theorems: Some surprising new results

    NASA Astrophysics Data System (ADS)

    Cerfon, Antoine; Freidberg, Jeffrey

    2009-05-01

    The classic MHD stability comparison theorems (Kruskal-Oberman, Rosenbluth-Rostoker) show that ideal MHD yields the most stringent stability limits according to the hierarchy δWCGL>δWKIN>δWMHD. This has long justified the use of ideal MHD for conservative predictions of MHD stability boundaries. We reexamine these theorems, with the following conclusions:(1) It is crucial to distinguish between ergodic and closed field line systems.(2) It is essential to account for resonant particles in the kinetic MHD model.(3) For ergodic systems the original kinetic MHD analysis over-estimates stability: δWKIN>δWMHD. Our new result predicts δWKIN=δWMHD.(4) For closed line systems plasma compressibility effects become important, and resonant particle effects vanish. Both the original and new analysis predict δWKIN>δWMHD. However, using a Vlasov-Fluid model with Vlasov ions and fluid electrons we show that both δWKIN and δWMHD, while mathematically correct, yield the wrong physical result. The V-F model shows that at marginal stability the compressibility stabilization term vanishes identically! For ergodic systems, marginal stability is always incompressible, so δWKIN=δWMHD=δWVF. For compressible modes in closed line systems, however, perpendicular resonant particle effects cancel the stabilizing effect of plasma compressibility predicted by ideal and kinetic MHD: δWKIN>δWMHD>δWVF.

  15. MHD performance demonstration experiment, FY 1974 to FY 1984

    NASA Astrophysics Data System (ADS)

    Whitehead, G. L.; Christensen, L. S.; Felderman, R. J.

    1984-06-01

    A national program for the development of commercial, open-cycle, magnetohydrodynamic (MHD) power generation is described. The emphasis of that national program was, and is, on establishing the engineering feasibilty of using coal to fuel the MHD power system. In order to establish feasibility it was necessary to experimentally demonstrate that an MHD generator system simulating a commercial-sized device can convert 16 to 18% of the available thermal energy into electric power at an isentropic efficiency of 60 to 70%. A presidential decree encouraged any government agency which might possess an organic MHD capability to assist ERDA in formulating and executing the national program. Since the largest MHD facility in the United States was located at the Arnold Engineering Development Center (AEDC), it was selected to be the national program element to demonstrate performance. As a result, the AEDC has been under contract since December 1973 (first to ERDA, later to its successor, the department of Energy, DOE) to modify existing equipment and to design, fabricate, and install new hardware to perform the MHD Performance Demonstration Experiment. The MHD facility is described and all results achieved to date are summarized.

  16. Power take-off analysis for diagonally connected MHD channels

    SciTech Connect

    Pan, Y C; Doss, E D

    1980-01-01

    The electrical loading of the power take-off region of diagonally connected MHD channels is investigated by a two-dimensional model. The study examines the loading schemes typical of those proposed for the U-25 and U-25 Bypass channels. The model is applicable for the following four cases: (1) connection with diodes only, (2) connection with diodes and equal resistors, (3) connection with diodes and variable resistances to obtain a given current distribution, and (4) connection with diodes and variable resistors under changing load. The analysis is applicable for the power take-off regions of single or multiple-output systems. The general behaviors of the current and the potential distributions in all four cases are discussed. The analytical results are in good agreement with the experimental data. It is found possible to design the electrical circuit of the channel in the take-off region so as to achieve a fairly even load current output under changing total load current.

  17. Suppression of MHD fluctuations leading to improved confinement in a gun-driven spheromak.

    PubMed

    McLean, H S; Woodruff, S; Hooper, E B; Bulmer, R H; Hill, D N; Holcomb, C; Moller, J; Stallard, B W; Wood, R D; Wang, Z

    2002-03-25

    Magnetic fluctuations have been reduced to approximately 1% during discharges on the Sustained Spheromak Physics Experiment by shaping the spatial distribution of the bias magnetic flux in the device. In the resulting quiescent regime, the safety factor profile is nearly flat in the plasma and the dominant ideal and resistive MHD modes are greatly reduced. During this period, the temperature profile is peaked at the magnetic axis and maps onto magnetic flux contours. Energy confinement time is improved over previous reports in a driven spheromak.

  18. Development of materials for open-cycle magnetohydrodynamics (MHD): ceramic electrode. Final report

    SciTech Connect

    Bates, J.L.; Marchant, D.D.

    1986-09-01

    Pacific Northwest Laboratory, supported by the US Department of Energy, developed advanced materials for use in open-cycle, closed cycle magnetohydrodynamics (MHD) power generation, an advanced energy conversion system in which the flow of electrically conducting fluid interacts with an electric field to convert the energy directly into electricity. The purpose of the PNL work was to develop electrodes for the MHD channel. Such electrodes must have: (1) electrical conductivity above 0.01 (ohm-cm)/sup -1/ from near room temperature to 1900/sup 0/K, (2) resistance to both electrochemical and chemical corrosion by both slag and potassium seed, (3) resistance to erosion by high-velocity gases and particles, (4) resistance to thermal shock, (5) adequate thermal conductivity, (6) compatibility with other channel components, particularly the electrical insulators, (7) oxidation-reduction stability, and (8) adequate thermionic emission. This report describes the concept and development of high-temperature, graded ceramic composite electrode materials and their electrical and structural properties. 47 refs., 16 figs., 13 tabs.

  19. Broken Symmetry and Coherent Structure in MHD Turbulence

    NASA Technical Reports Server (NTRS)

    Shebalin, John V.

    2007-01-01

    Absolute equilibrium ensemble theory for ideal homogeneous magnetohydrodynamic (MHD) turbulence is fairly well developed. Theory and Simulation indicate that ideal MHD turbulence non-ergodic and contains coherent structure. The question of applicability real (i.e., dissipative) MHD turbulence is examined. Results from several very long time numerical simulations on a 64(exp 3) grid are presented. It is seen that coherent structure begins to form before decay dominates over nonlinearity. The connection with inverse spectral cascades and selective decay will also be discussed.

  20. A summary of the ECAS MHD power plant results

    NASA Technical Reports Server (NTRS)

    Seikel, G. R.; Harris, L. P.

    1976-01-01

    The performance and the cost of electricity (COE) for MHD systems utilizing coal or coal derived fuels are summarized along with a conceptual open cycle MHD plant design. The results show that open cycle coal fired recuperatively preheated MHD systems have potentially one of the highest coal-pile-to-bus bar efficiencies (48.3%) and also one of the lowest COE of the systems studied. Closed cycle, inert gas systems do not appear to have the potential of exceeding the efficiency of or competing with the COE of advanced steam plants.

  1. A helically distorted MHD flux rope model

    NASA Technical Reports Server (NTRS)

    Theobald, Michael L.; Montgomery, David

    1990-01-01

    A flux rope model is proposed which has a variable degree of helical distortion from axisymmetry. The basis for this suggestion is a series of numerical and analytical investigations of magnetohydrodynamic states which result when an axial electric current is directed down on dc magnetic field. The helically distorted states involve a flow velocity and seem to be favored because of their lower rate of energy dissipation. Emphasis is on the magnetometer and particle energy analyzer traces that might be characteristic of such flux ropes. It is shown that even a fractionally small helical distortion may considerably alter the traces in minimum-variance coordinates. In short, what may be fairly common MHD processes can render a flux rope almost unrecognizable under standard diagnostics, even if the departures from axisymmetry are not great.

  2. Global MHD Models of the Solar Corona

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Rose, Franklin (Technical Monitor)

    2001-01-01

    Global magnetohydrodynamic (MHD) models of the solar corona are computationally intensive, numerically complex simulations that have produced important new results over the past few years. After a brief overview of how these models usually work, I will address three topics: (1) How these models are now routinely used to predict the morphology of the corona and analyze Earth and space-based remote observations of the Sun; (2) The direct application of these models to the analysis of physical processes in the corona and chromosphere and to the interpretation of in situ solar wind observations; and (3) The use of results from global models to validate the approximations used to make detailed studies of physical processes in the corona that are not otherwise possible using the global models themselves.

  3. Drag reduction in turbulent MHD pipe flows

    NASA Technical Reports Server (NTRS)

    Orlandi, P.

    1996-01-01

    This is a preliminary study devoted to verifying whether or not direct simulations of turbulent Magneto-Hydro-Dynamic (MHD) flows in liquid metals reproduce experimental observations of drag reduction. Two different cases have been simulated by a finite difference scheme which is second order accurate in space and time. In the first case, an external azimuthal magnetic field is imposed. In this case, the magnetic field acts on the mean axial velocity and complete laminarization of the flow at N(sub a) = 30 has been achieved. In the second case, an axial magnetic field is imposed which affects only fluctuating velocities, and thus the action is less efficient. This second case is more practical, but comparison between numerical and experimental results is only qualitative.

  4. Numerical linearized MHD model of flapping oscillations

    NASA Astrophysics Data System (ADS)

    Korovinskiy, D. B.; Ivanov, I. B.; Semenov, V. S.; Erkaev, N. V.; Kiehas, S. A.

    2016-06-01

    Kink-like magnetotail flapping oscillations in a Harris-like current sheet with earthward growing normal magnetic field component Bz are studied by means of time-dependent 2D linearized MHD numerical simulations. The dispersion relation and two-dimensional eigenfunctions are obtained. The results are compared with analytical estimates of the double-gradient model, which are found to be reliable for configurations with small Bz up to values ˜ 0.05 of the lobe magnetic field. Coupled with previous results, present simulations confirm that the earthward/tailward growth direction of the Bz component acts as a switch between stable/unstable regimes of the flapping mode, while the mode dispersion curve is the same in both cases. It is confirmed that flapping oscillations may be triggered by a simple Gaussian initial perturbation of the Vz velocity.

  5. Multimegawatt NEP with vapor core reactor MHD

    NASA Astrophysics Data System (ADS)

    Smith, Blair; Knight, Travis; Anghaie, Samim

    2002-01-01

    Efforts at the Innovative Nuclear Space Power and Propulsion Institute have assessed the feasibility of combining gaseous or vapor core reactors with magnetohydrodynamic power generators to provide extremely high quality, high density, and low specific mass electrical power for space applications. Innovative shielding strategies are employed to maintain an effective but relatively low mass shield, which is the most dominating part of multi-megawatt space power systems. The fission driven magnetohydrodynamic generator produces tens of kilowatt DC power at specific mass of less than 0.5 kg/kW for the total power system. The MHD output with minor conditioning is coupled to magnetoplasmadynamic thruster to achieve an overall NEP system specific mass of less than 1.0 kg/kW for power levels above 20 MWe. Few other concepts would allow comparable ensuing payload savings and flexible mission abort options for manned flights to Mars for example. .

  6. MHD simulation of the Bastille day event

    NASA Astrophysics Data System (ADS)

    Linker, Jon; Torok, Tibor; Downs, Cooper; Lionello, Roberto; Titov, Viacheslav; Caplan, Ronald M.; Mikić, Zoran; Riley, Pete

    2016-03-01

    We describe a time-dependent, thermodynamic, three-dimensional MHD simulation of the July 14, 2000 coronal mass ejection (CME) and flare. The simulation starts with a background corona developed using an MDI-derived magnetic map for the boundary condition. Flux ropes using the modified Titov-Demoulin (TDm) model are used to energize the pre-event active region, which is then destabilized by photospheric flows that cancel flux near the polarity inversion line. More than 1033 ergs are impulsively released in the simulated eruption, driving a CME at 1500 km/s, close to the observed speed of 1700km/s. The post-flare emission in the simulation is morphologically similar to the observed post-flare loops. The resulting flux rope that propagates to 1 AU is similar in character to the flux rope observed at 1 AU, but the simulated ICME center passes 15° north of Earth.

  7. General Relativistic MHD Simulations of Jet Formation

    NASA Technical Reports Server (NTRS)

    Mizuno, Y.; Nishikawa, K.-I.; Hardee, P.; Koide, S.; Fishman, G. J.

    2005-01-01

    We have performed 3-dimensional general relativistic magnetohydrodynamic (GRMHD) simulations of jet formation from an accretion disk with/without initial perturbation around a rotating black hole. We input a sinusoidal perturbation (m = 5 mode) in the rotation velocity of the accretion disk. The simulation results show the formation of a relativistic jet from the accretion disk. Although the initial perturbation becomes weakened by the coupling among different modes, it survives and triggers lower modes. As a result, complex non-axisymmetric density structure develops in the disk and the jet. Newtonian MHD simulations of jet formation with a non-axisymmetric mode show the growth of the m = 2 mode but GRMHD simulations cannot see the clear growth of the m = 2 mode.

  8. A Two-Fluid, MHD Coronal Model

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

    1999-01-01

    We describe first results from a numerical two-fluid MHD model of the global structure of the solar Corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and Momentum sources are required to produce high speed wind from Corona] holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer the temperature and density are similar to those reported empirically by Li et al. [1998], and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub S), as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

  9. A Two-Fluid, MHD Coronal Model

    NASA Technical Reports Server (NTRS)

    Suess, Steven T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

    1998-01-01

    We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.

  10. High incidence of antimicrobial resistant organisms including extended spectrum beta-lactamase producing Enterobacteriaceae and methicillin-resistant Staphylococcus aureus in nasopharyngeal and blood isolates of HIV-infected children from Cape Town, South Africa

    PubMed Central

    Cotton, Mark F; Wasserman, Elizabeth; Smit, Juanita; Whitelaw, Andrew; Zar, Heather J

    2008-01-01

    Background There is little information on nasopharyngeal (NP) flora or bacteremia in HIV-infected children. Our aim was to describe the organisms and antimicrobial resistance patterns in children enrolled in a prospective study comparing daily and three times weekly trimethoprim-sulfamethoxazole (TMP-SMX) and isoniazid (INH) or placebo prophylaxis. Methods NP swabs were taken at baseline from HIV-infected children enrolled in the study. Standard microbiological techniques were used. Children were grouped according to previous or current exposure to TMP-SMX and whether enrolled to the study during a period of hospitalization. Blood culture results were also recorded within 12 months of baseline. Results Two hundred and three children, median age 1.8 (Interquartile [IQ]: 0.7–4) years had NP swabs submitted for culture. One hundred and eighty-four (90.7%) had either stage B or C HIV disease. One hundred and forty-one (69.8%) were receiving TMP-SMX and 19 (9.4%) were on antiretroviral therapy. The majority, 168 (82%) had a history of hospitalization and 91 (44.8%) were enrolled during a period of hospitalization. Thirty-two subjects (16.2%) died within 12 months of study entry. One hundred and eighty-one potential pathogens were found in 167 children. The most commonly isolated organisms were Streptococcus pneumoniae (48: 22.2%), Gram-negative respiratory organisms (Haemophilus influenzae and Moraxella catarrhalis) (47: 21.8%), Staphylococcus aureus (44: 20.4%), Enterobacteriaceae 32 (14.8%) and Pseudomonas 5 (2.3%). Resistance to TMP-SMX occurred in > 80% of pathogens except for M. catarrhalis (2: 18.2% of tested organisms). TMP-SMX resistance tended to be higher in those receiving it at baseline (p = 0.065). Carriage of Methicillin resistant S. aureus (MRSA) was significantly associated with being on TMP-SMX at baseline (p = 0.002). Minimal inhibitory concentrations (MIC) to penicillin were determined for 18 S. pneumoniae isolates: 7 (38.9%) were fully sensitive

  11. Two crystal structures of dihydrofolate reductase-thymidylate synthase from Cryptosporidium hominis reveal protein–ligand interactions including a structural basis for observed antifolate resistance

    SciTech Connect

    Anderson, Amy C.

    2005-03-01

    An analysis of the protein–ligand interactions in two crystal structures of DHFR-TS from C. hominis reveals a possible structural basis for observed antifolate resistance in C. hominis DHFR. A comparison with the structure of human DHFR reveals residue substitutions that may be exploited for the design of species-selective inhibitors. Cryptosporidium hominis is a protozoan parasite that causes acute gastrointestinal illness. There are no effective therapies for cryptosporidiosis, highlighting the need for new drug-lead discovery. An analysis of the protein–ligand interactions in two crystal structures of dihydrofolate reductase-thymidylate synthase (DHFR-TS) from C. hominis, determined at 2.8 and 2.87 Å resolution, reveals that the interactions of residues Ile29, Thr58 and Cys113 in the active site of C. hominis DHFR provide a possible structural basis for the observed antifolate resistance. A comparison with the structure of human DHFR reveals active-site differences that may be exploited for the design of species-selective inhibitors.

  12. A cluster of at least three esterase genes in Lucilia cuprina includes malathion carboxylesterase and two other esterases implicated in resistance to organophosphates

    SciTech Connect

    Smyth, K.A. |; Russell, R.J.; Oakeshott, J.G.

    1994-12-01

    Three distinct malathion carboxylesterase (MCE) phenotypes have been identified among strains of Lucilia cuprina. The high-activity phenotype shows 1.6- and 3.3-fold more MCE specific activity than the intermediate- and low-activity phenotypes, respectively. Flies with high MCE activity are 1000-fold more resistant to malathion than flies with either low or intermediate MCE phenotypes, which are equally susceptible. High and low MCE specific activity are allelic and encoded by the Rmal gene on chromosome 4. Rmal is clustered within one map unit of two other esterase genes, Rop1 and E9, which are implicated in resistance to other organophosphate insecticides. Intermediate MCE specific activity is also inherited within the cluster, although its allelism to Rmal, Rop1, or E9 is unclear. The cluster does not contain the gene for the hemolymph esterase E4, which maps 6.1 map units from Rop1, on the other side of the bubbled wing marker. The cluster appears to be homologous to part of a tandem array of 11 esterase genes on chromosome 3R of Drosophila melanogaster. 41 refs., 4 figs., 2 tabs.

  13. Strengths and limitations of various screening methods for carbapenem-resistant Enterobacteriaceae including new method recommended by clinical and laboratory standards institute, 2017: A tertiary care experience.

    PubMed

    Pragasam, Agila Kumari; Veeraraghavan, Balaji; Bakthavatchalam, Yamuna Devi; Gopi, Radha; Aslam, Raziya Fathima

    2017-01-01

    Carbapenemase-mediated carbapenem resistance is a major concern across the world. Rapid detection of carbapenemase-producing organisms is of great importance in clinical settings. However, it is essential to have a test with good sensitivity and specificity. The aim of the study was to compare the performance of RAPIDEC® CARBA NP and modified carbapenem inactivation method (mCIM) recommended by Clinical and Laboratory Standards Institute guideline 2017. A total of ninety carbapenem resistant Escherichia coli and Klebsiella pneumoniae have been tested. The presence of various carbapenemases was screened by conventional multiplex polymerase chain reaction. RAPIDEC® CARBA NP detected 90%, whereas mCIM detected 99% of the study isolates tested. Although RAPIDEC® CARBA NP is a rapid test, the sensitivity is reduced for blaOxa-48Likedetection; while mCIM could pick up blaOxa-48Likeenzymes with excellent sensitivity. Further, organisms producing low carbapenemase activity enzymes, thickness of the inoculum and the disc potency are likely to influence the test results of mCIM with an overnight delay.

  14. Statistical comparison of inter-substorm timings in global magnetohydrodynamics (MHD) and observations

    NASA Astrophysics Data System (ADS)

    Haiducek, J. D.; Welling, D. T.; Morley, S.; Ozturk, D. S.

    2015-12-01

    Magnetospheric substorms are events in which energy stored in the magnetotail is released into the auroral zone and into the downstream solar wind. Because of the complex, nonlinear, and possibly chaotic nature of the substorm energy release mechanism, it may be extremely difficult to forecast individual substorms in the near term. However, the inter-substorm timing (the amount of time elapsed between substorms) can be reproduced in a statistical sense, as was demonstrated by Freeman and Morley (2004) using their Minimal Substorm Model (MSM), a simple solar-wind driven model with the only free parameter being a recurrence time. The goal of the present work is to reproduce the observed distribution of inter-substorm timings with a global MHD model. The period of 1-31 January 2005 was simulated using the Space Weather Modeling Framework (SWMF), driven by solar wind observations. Substorms were identified in the model output by synthesizing surface magnetometer data and by looking for tailward-moving plasmoids. Substorms identified in the MHD model are then compared with observational data from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, Los Alamos National Laboratory (LANL) geostationary satellite energetic particle data, and surface magnetometer data. For each dataset (MHD model and observations), we calculate the substorm occurrence rate, and for the MHD model we additionally calculate the timing error of the substorm onsets relative to the observed substorms. Finally, we calculate distribution functions for the inter-substorm timings in both the observations and the model. The results of this analysis will guide improvements to the MHD-based substorm model, including the use of Hall MHD and embedded particle in cell (EPIC), leading to a better reproduction of the observed inter-substorm timings and an improved understanding of the underlying physical processes. ReferencesM. P. Freeman and S. K. Morley. A minimal substorm model that

  15. Io's Magnetospheric Interaction: An MHD Model with Day-Night Asymmetry

    NASA Technical Reports Server (NTRS)

    Kabin, K.; Combi, M. R.; Gombosi, T. I.; DeZeeuw, D. L.; Hansen, K. C.; Powell, K. G.

    2001-01-01

    In this paper we present the results of all improved three-dimensional MHD model for Io's interaction with Jupiter's magnetosphere. We have included the day-night asymmetry into the spatial distribution of our mass-loading, which allowed us to reproduce several smaller features or the Galileo December 1995 data set. The calculation is performed using our newly modified description of the pick-up processes that accounts for the effects of the corotational electric field existing in the Jovian magnetosphere. This change in the formulation of the source terms for the MHD equations resulted in significant improvements in the comparison with the Galileo measurements. We briefly discuss the limitations of our model and possible future improvements.

  16. Calculating Pressure-Driven Current Near Magnetic Islands for 3D MHD Equilibria

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, Dhanush; Reiman, Allan

    2016-10-01

    In general, 3D MHD equilibria in toroidal plasmas do not result in nested pressure surfaces. Instead, islands and chaotic regions appear in the equilibrium. Near small magnetic islands, the pressure varies within the flux surfaces, which has a significant effect on the pressure-driven current, introducing singularities. Previously, the MHD equilibrium current near a magnetic island was calculated, including the effect of ``stellarator symmetry,'' wherein the singular components of the pressure-driven current vanish [A. H. Reiman, Phys. Plasmas 23, 072502 (2016)]. Here we first solve for pressure in a cylindrical plasma from the heat diffusion equation, after adding a helical perturbation. We then numerically calculate the corresponding Pfirsch-Schluter current. At the small island limit, we compare the pressure-driven current with the previously calculated solution, and far from the island, we recover the solution for nested flux surfaces. Lastly, we compute the current for a toroidal plasma for symmetric and non-symmetric geometries.

  17. Alfvén ionization in an MHD-gas interactions code

    NASA Astrophysics Data System (ADS)

    Wilson, A. D.; Diver, D. A.

    2016-07-01

    A numerical model of partially ionized plasmas is developed in order to capture their evolving ionization fractions as a result of Alfvén ionization (AI). The mechanism of, and the parameter regime necessary for, AI is discussed and an expression for the AI rate based on fluid parameters, from a gas-MHD model, is derived. This AI term is added to an existing MHD-gas interactions' code, and the result is a linear, 2D, two-fluid model that includes momentum transfer between charged and neutral species as well as an ionization rate that depends on the velocity fields of both fluids. The dynamics of waves propagating through such a partially ionized plasma are investigated, and it is found that AI has a significant influence on the fluid dynamics as well as both the local and global ionization fraction.

  18. Ion Loss from Titan's Atmosphere versus Local Time: A two-fluid MHD Study

    NASA Astrophysics Data System (ADS)

    Ma, Y.; Russell, C. T.; Nagy, A. F.; Toth, G.; Dougherty, M. K.; Cravens, T. E.; Wellbrock, A.; Coates, A. J.; Garnier, P.; Wahlund, J.; Crary, F. J.

    2009-12-01

    This presentation report recent progress on modeling of plasma interaction around Titan. The single fluid MHD model reproduces only the sum of the electron temperature and ion temperature. Our recent modeling includes an electron energy equation in the Hall MHD model so that both electron temperature and ion temperature ARE self-consistently calculated. The plasma interaction with Titan is expected to vary as the moon moves around its orbit. Using the improved model, we compare the structure of the interaction under two extreme conditions, corresponding to upstream flow interacting with the nightside and dayside ionosphere respectively. Model results show that the dayside ionosphere is more extended and the flow is more disturbed in the 6 SLT case than in the 18 SLT case. We calculate the ion escape rates under these conditions and compare with Cassini observations of the only two available low altitudes Cassini flybys in Saturn's dawn (T5 flyby) and dusk (T34 flyby) sectors.

  19. Observation of SOL Current Correlated with MHD Activity in NBI-heated DIII-D Tokamak Discharges

    SciTech Connect

    H. Takahashi; E.D. Fredrickson; M.J. Schaffer; M.E. Austin; T.E. Evans; L.L. Lao; J.G. Watkins

    2004-03-26

    This work investigates the potential roles played by the scrape-off-layer current (SOLC) in MHD activity of tokamak plasmas, including effects on stability. SOLCs are found during MHD activity that are: (1) slowly growing after a mode-locking-like event, (2) oscillating in the several kHz range and phase-locked with magnetic and electron temperature oscillations, (3) rapidly growing with a sub-ms time scale during a thermal collapse and a current quench, and (4) spiky in temporal behavior and correlated with spiky features in Da signals commonly identified with the edge localized mode (ELM). These SOLCs are found to be an integral part of the MHD activity, with a propensity to flow in a toroidally non-axisymmetric pattern and with magnitude potentially large enough to play a role in the MHD stability. Candidate mechanisms that can drive these SOLCs are identified: (a) toroidally non-axisymmetric thermoelectric potential, (b) electromotive force (EMF) from MHD activity, and (c) flux swing, both toroidal and poloidal, of the plasma column. An effect is found, stemming from the shear in the field line pitch angle, that mitigates the efficacy of a toroidally non-axisymmetric SOLC to generate a toroidally non-axisymmetric error field. Other potential magnetic consequences of the SOLC are identified: (i) its error field can introduce complications in feedback control schemes for stabilizing MHD activity and (ii) its toroidally non-axisymmetric field can be falsely identified as an axisymmetric field by the tokamak control logic and in equilibrium reconstruction. The radial profile of a SOLC observed during a quiescent discharge period is determined, and found to possess polarity reversals as a function of radial distance.

  20. Possible uses for Phillips Laboratory MHD generator. Final report, 1 October 1994-30 August 1995

    SciTech Connect

    Turchi, P.J.

    1995-08-01

    There is interest in electromagnetic energy sources for applications to directed energy weapons. Candidates include portable conventional rotating machinery electric generators, magnetic flux compression generators (aka explosive generators, magnetocumulative generators or MCGs) based on explosive action, and magnetohydrodynamic (MHD) generators using chemical energy of explosives or rocket propellants. For portable high energy MHD generators, US technology base appeared to need rescue. The US has received a MHD device in the PAMlR-3U, developed in the former Soviet Union. The present discussion considers uses of this generator for programs on high-power microwave systems and other directed energy concepts. Future applications will be limited by development and funding of specific technical needs. A useful next step would be detailed design of a system to charge high-voltage pulsers. This design should include comparison of single-pulse switching to achieve high-voltage from an inductive storage coil (energy storage option) vs repetitive switching at low voltage, followed by custom built transformers (direct drive option).

  1. Diagnostic development and support of MHD (magnetohydrodynamics) test facilities

    SciTech Connect

    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.

  2. TRANSITION FROM KINETIC TO MHD BEHAVIOR IN A COLLISIONLESS PLASMA

    SciTech Connect

    Parashar, Tulasi N.; Matthaeus, William H.; Shay, Michael A.; Wan, Minping

    2015-10-01

    The study of kinetic effects in heliospheric plasmas requires representation of dynamics at sub-proton scales, but in most cases the system is driven by magnetohydrodynamic (MHD) activity at larger scales. The latter requirement challenges available computational resources, which raises the question of how large such a system must be to exhibit MHD traits at large scales while kinetic behavior is accurately represented at small scales. Here we study this implied transition from kinetic to MHD-like behavior using particle-in-cell (PIC) simulations, initialized using an Orszag–Tang Vortex. The PIC code treats protons, as well as electrons, kinetically, and we address the question of interest by examining several different indicators of MHD-like behavior.

  3. Transition from Kinetic to MHD Behavior in a Collisionless Plasma

    NASA Astrophysics Data System (ADS)

    Parashar, Tulasi N.; Matthaeus, William H.; Shay, Michael A.; Wan, Minping

    2015-10-01

    The study of kinetic effects in heliospheric plasmas requires representation of dynamics at sub-proton scales, but in most cases the system is driven by magnetohydrodynamic (MHD) activity at larger scales. The latter requirement challenges available computational resources, which raises the question of how large such a system must be to exhibit MHD traits at large scales while kinetic behavior is accurately represented at small scales. Here we study this implied transition from kinetic to MHD-like behavior using particle-in-cell (PIC) simulations, initialized using an Orszag-Tang Vortex. The PIC code treats protons, as well as electrons, kinetically, and we address the question of interest by examining several different indicators of MHD-like behavior.

  4. MHD generator component development. Quarterly report, July 1983-September 1983

    SciTech Connect

    Not Available

    1983-11-01

    The overall objectives of this program are two-fold: (1) To contribute, by appropriate systematic experimental and analytical investigations, to the engineering data base necessary for the design and construction of MHD generators at CDIF-scale (50 MW/sub th/) and baseload scale (2000 MW/sub th/). (2) To design and fabricate specific hardware items to be tested at the CDIF site in Butte, Montana. The program consists of a series of related tasks: (1) MHD channel design and performance; (2) MHD channel construction and lifetime; (3) MHD channel loading and control; (4) facility operation; (5) CDIF related hardware; and (6) high interaction tests of a supersonic channel. Progress is reported. (WHK)

  5. Energy exchange and wave action conservation for magnetohydrodynamic (MHD) waves in a general, slowly varying medium

    NASA Astrophysics Data System (ADS)

    Walker, A. D. M.

    2014-12-01

    Magnetohydrodynamic (MHD) waves in the solar wind and magnetosphere are propagated in a medium whose velocity is comparable to or greater than the wave velocity and which varies in both space and time. In the approximation where the scales of the time and space variation are long compared with the period and wavelength, the ray-tracing equations can be generalized and then include an additional first-order differential equation that determines the variation of frequency. In such circumstances the wave can exchange energy with the background: wave energy is not conserved. In such processes the wave action theorem shows that the wave action, defined as the ratio of the wave energy to the frequency in the local rest frame, is conserved. In this paper we discuss ray-tracing techniques and the energy exchange relation for MHD waves. We then provide a unified account of how to deal with energy transport by MHD waves in non-uniform media. The wave action theorem is derived directly from the basic MHD equations for sound waves, transverse Alfvén waves, and the fast and slow magnetosonic waves. The techniques described are applied to a number of illustrative cases. These include a sound wave in a medium undergoing a uniform compression, an isotropic Alfvén wave in a steady-state shear layer, and a transverse Alfvén wave in a simple model of the magnetotail undergoing compression. In each case the nature and magnitude of the energy exchange between wave and background is found.

  6. Induction of vacuolar invertase inhibitor mRNA in potato tubers contributes to cold-induced sweetening resistance and includes spliced hybrid mRNA variants.

    PubMed

    Brummell, David A; Chen, Ronan K Y; Harris, John C; Zhang, Huaibi; Hamiaux, Cyril; Kralicek, Andrew V; McKenzie, Marian J

    2011-06-01

    Cold storage of tubers of potato (Solanum tuberosum L.) compromises tuber quality in many cultivars by the accumulation of hexose sugars in a process called cold-induced sweetening. This is caused by the breakdown of starch to sucrose, which is cleaved to glucose and fructose by vacuolar acid invertase. During processing of affected tubers, the high temperatures involved in baking and frying cause the Maillard reaction between reducing sugars and free amino acids, resulting in the accumulation of acrylamide. cDNA clones with deduced proteins homologous to known invertase inhibitors were isolated and the two most abundant forms, termed INH1 and INH2, were shown to possess apoplastic and vacuolar localization, respectively. The INH2 gene showed developmentally regulated alternative splicing, so, in addition to the INH2α transcript encoding the full-length protein, two hybrid mRNAs (INH2β*A and INH2β*B) that encoded deduced vacuolar invertase inhibitors with divergent C-termini were detected, the result of mRNA splicing of an upstream region of INH2 to a downstream region of INH1. Hybrid RNAs are common in animals, where they may add to the diversity of the proteome, but are rarely described in plants. During cold storage, INH2α and the hybrid INH2β mRNAs accumulated to higher abundance in cultivars resistant to cold-induced sweetening than in susceptible cultivars. Increased amounts of invertase inhibitor may contribute to the suppression of acid invertase activity and prevent cleavage of sucrose. Evidence for increased RNA splicing activity was detected in several resistant lines, a mechanism that in some circumstances may generate a range of proteins with additional functional capacity to aid adaptability.

  7. Induction of vacuolar invertase inhibitor mRNA in potato tubers contributes to cold-induced sweetening resistance and includes spliced hybrid mRNA variants

    PubMed Central

    Brummell, David A.; Chen, Ronan K. Y.; Harris, John C.; Zhang, Huaibi; Hamiaux, Cyril; Kralicek, Andrew V.; McKenzie, Marian J.

    2011-01-01

    Cold storage of tubers of potato (Solanum tuberosum L.) compromises tuber quality in many cultivars by the accumulation of hexose sugars in a process called cold-induced sweetening. This is caused by the breakdown of starch to sucrose, which is cleaved to glucose and fructose by vacuolar acid invertase. During processing of affected tubers, the high temperatures involved in baking and frying cause the Maillard reaction between reducing sugars and free amino acids, resulting in the accumulation of acrylamide. cDNA clones with deduced proteins homologous to known invertase inhibitors were isolated and the two most abundant forms, termed INH1 and INH2, were shown to possess apoplastic and vacuolar localization, respectively. The INH2 gene showed developmentally regulated alternative splicing, so, in addition to the INH2α transcript encoding the full-length protein, two hybrid mRNAs (INH2β*A and INH2β*B) that encoded deduced vacuolar invertase inhibitors with divergent C-termini were detected, the result of mRNA splicing of an upstream region of INH2 to a downstream region of INH1. Hybrid RNAs are common in animals, where they may add to the diversity of the proteome, but are rarely described in plants. During cold storage, INH2α and the hybrid INH2β mRNAs accumulated to higher abundance in cultivars resistant to cold-induced sweetening than in susceptible cultivars. Increased amounts of invertase inhibitor may contribute to the suppression of acid invertase activity and prevent cleavage of sucrose. Evidence for increased RNA splicing activity was detected in several resistant lines, a mechanism that in some circumstances may generate a range of proteins with additional functional capacity to aid adaptability. PMID:21393382

  8. HVEPS Scramjet-Driven MHD Power Demonstration Test Results (Preprint)

    DTIC Science & Technology

    2007-06-01

    direct connect mode with a vacuum air ejector exhaust system that holds back pressure to about 4.0 psia in the downsteam exhaust quench tank ...analytical verification. The static pressure distribution data in comparison to CFD results and past tests, provides a high degree of confidence that... pressure , high temperature combustor to produce a high velocity plasma, flow that drives the MHD generator. The self-contained combustion-driven MHD

  9. MHD turbulence, reconnection, and test-particle acceleration

    NASA Technical Reports Server (NTRS)

    Gray, Perry C.; Matthaeus, William H.

    1992-01-01

    We examine homogeneous MHD turbulence and turbulent magnetic reconnection as possible mechanisms for accelerating cosmic ray particles. Test particle calculations are performed using fields from MHD simulations, and initially Maxwellian particle distributions are shown to evolve into power-law distributions. Simple estimates for both the maximum energy attainable and the mean energies of the accelerated particles are fairly successful and are consistent with timescales for flares and cosmic rays.

  10. An experimental studies with disk MHD channels on argon plazma

    SciTech Connect

    Koneev, S.M.A.; Kovalev, L.K.; Larionoff, A.E.; Poltavets, V.N.

    1994-12-31

    The most interesting works carried out over the past few years in the field of MHD generating electric power are the ones studying disk MHD channels. The results published give a hope to overcome one of the MHD generator essential disadvantages - relatively low effectiveness of converting heat power into electric one. In some works performed by different authors and at different plants the coefficients of energy conversion achieving 20% have been obtained and there is a hint of the future possible increase of up to 40%. In the majority of experimental studies non-equilibrium ionized inertial gases (Ar, He) with alkali metal (Cs, K) were used as a working medium, the operating temperature being 1800-2000 K. The present paper is dedicated to an experimental test rig-with-a-disk-MHD-channel development for operating on thermally ionized Ar with the temperature of up to 9000 K and pressure 10 up to 10 Pa. For heating a working medium an electric arc in a special plazmotron is used. As the experiments on linear MHD channels have shown, along the whole working area the plasma is non-equilibrium with a substantial break off of an electron temperature providing conductivity of more then 100 Sm/m. The aim of creation this test rig is in simulating the processes of the working medium flow and electric energy generation in disk MHD channels. An important research element is calculation techniques debugging and acquiring experience of development and carrying out disk MHD generator studies for the following experimental full-scale MHD plants with a disk channel to be created.

  11. Evaluation of the ECAS open cycle MHD power plant design

    NASA Technical Reports Server (NTRS)

    Seikel, G. R.; Staiger, P. J.; Pian, C. C. P.

    1978-01-01

    The Energy Conversion Alternatives Study (ECAS) MHD/steam power plant is described. The NASA critical evaluation of the design is summarized. Performance of the MHD plant is compared to that of the other type ECAS plant designs on the basis of efficiency and the 30-year levelized cost of electricity. Techniques to improve the plant design and the potential performance of lower technology plants requiring shorter development time and lower development cost are then discussed.

  12. Positive selection for resistance to 2-deoxyglucose gives rise, in Streptococcus salivarius, to seven classes of pleiotropic mutants, including ptsH and ptsI missense mutants.

    PubMed

    Gauthier, L; Thomas, S; Gagnon, G; Frenette, M; Trahan, L; Vadeboncoeur, C

    1994-09-01

    We have used the toxic non-metabolizable glucose/mannose analogue 2-deoxyglucose to isolate a comprehensive collection of mutants of the phosphoenolpyruvate:sugar phosphotransferase system from Streptococcus salivarius. To increase the range of possible mutations, we isolated spontaneous mutants on different media containing 2-deoxyglucose and various metabolizable sugars, either lactose, melibiose, galactose or fructose. We found that the frequency at which 2-deoxyglucose-resistant mutants were isolated varied according to the growth substrate. The highest frequency was obtained with the combination galactose and 2-deoxyglucose and was 15-fold higher than the rate observed with the mixture melibiose and 2-deoxyglucose, the combination that gave the lowest frequency. By combining results from: (i) Western blot analysis of IIIMan, a specific component of the phosphoenolpyruvate:mannose phosphotransferase system in S. salivarius; (ii) rocket immunoelectrophoresis of HPr and EI, the two general energy-coupling proteins of the phosphotransferase system; and (iii) from gene sequencing, mutants could be assigned to seven classes.(ABSTRACT TRUNCATED AT 250 WORDS)

  13. Pulse Detonation Rocket MHD Power Experiment

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Cook, Stephen (Technical Monitor)

    2002-01-01

    A pulse detonation research engine (MSFC (Marshall Space Flight Center) Model PDRE (Pulse Detonation Rocket Engine) G-2) has been developed for the purpose of examining integrated propulsion and magnetohydrodynamic power generation applications. The engine is based on a rectangular cross-section tube coupled to a converging-diverging nozzle, which is in turn attached to a segmented Faraday channel. As part of the shakedown testing activity, the pressure wave was interrogated along the length of the engine while running on hydrogen/oxygen propellants. Rapid transition to detonation wave propagation was insured through the use of a short Schelkin spiral near the head of the engine. The measured detonation wave velocities were in excess of 2500 m/s in agreement with the theoretical C-J velocity. The engine was first tested in a straight tube configuration without a nozzle, and the time resolved thrust was measured simultaneously with the head-end pressure. Similar measurements were made with the converging-diverging nozzle attached. The time correlation of the thrust and head-end pressure data was found to be excellent. The major purpose of the converging-diverging nozzle was to configure the engine for driving an MHD generator for the direct production of electrical power. Additional tests were therefore necessary in which seed (cesium-hydroxide dissolved in methanol) was directly injected into the engine as a spray. The exhaust plume was then interrogated with a microwave interferometer in an attempt to characterize the plasma conditions, and emission spectroscopy measurements were also acquired. Data reduction efforts indicate that the plasma exhaust is very highly ionized, although there is some uncertainty at this time as to the relative abundance of negative OH ions. The emission spectroscopy data provided some indication of the species in the exhaust as well as a measurement of temperature. A 24-electrode-pair segmented Faraday channel and 0.6 Tesla permanent

  14. FOI-PERFECT code: 3D relaxation MHD modeling and Applications

    NASA Astrophysics Data System (ADS)

    Wang, Gang-Hua; Duan, Shu-Chao; Comutational Physics Team Team

    2016-10-01

    One of the challenges in numerical simulations of electromagnetically driven high energy density (HED) systems is the existence of vacuum region. FOI-PERFECT code adopts a full relaxation magnetohydrodynamic (MHD) model. The electromagnetic part of the conventional model adopts the magnetic diffusion approximation. The vacuum region is approximated by artificially increasing the resistivity. On one hand the phase/group velocity is superluminal and hence non-physical in the vacuum region, on the other hand a diffusion equation with large diffusion coefficient can only be solved by implicit scheme which is difficult to be parallelized and converge. A better alternative is to solve the full electromagnetic equations. Maxwell's equations coupled with the constitutive equation, generalized Ohm's law, constitute a relaxation model. The dispersion relation is given to show its transition from electromagnetic propagation in vacuum to resistive MHD in plasma in a natural way. The phase and group velocities are finite for this system. A better time stepping is adopted to give a 3rd full order convergence in time domain without the stiff relaxation term restriction. Therefore it is convenient for explicit & parallel computations. Some numerical results of FOI-PERFECT code are also given. Project supported by the National Natural Science Foundation of China (Grant No. 11571293) And Foundation of China Academy of Engineering Physics (Grant No. 2015B0201023).

  15. NON-IDEAL MHD EFFECTS AND MAGNETIC BRAKING CATASTROPHE IN PROTOSTELLAR DISK FORMATION

    SciTech Connect

    Li Zhiyun; Krasnopolsky, Ruben; Shang Hsien

    2011-09-10

    Dense, star-forming cores of molecular clouds are observed to be significantly magnetized. A realistic magnetic field of moderate strength has been shown to suppress, through catastrophic magnetic braking, the formation of a rotationally supported disk (RSD) during the protostellar accretion phase of low-mass star formation in the ideal MHD limit. We address, through two-dimensional (axisymmetric) simulations, the question of whether realistic levels of non-ideal effects, computed with a simplified chemical network including dust grains, can weaken the magnetic braking enough to enable an RSD to form. We find that ambipolar diffusion (AD), the dominant non-ideal MHD effect over most of the density range relevant to disk formation, does not enable disk formation, at least in two dimensions. The reason is that AD allows the magnetic flux that would be dragged into the central stellar object in the ideal MHD limit to pile up instead in a small circumstellar region, where the magnetic field strength (and thus the braking efficiency) is greatly enhanced. We also find that, on the scale of tens of AU or more, a realistic level of Ohmic dissipation does not weaken the magnetic braking enough for an RSD to form, either by itself or in combination with AD. The Hall effect, the least explored of these three non-ideal MHD effects, can spin up the material close to the central object to a significant, supersonic rotation speed, even when the core is initially non-rotating, although the spun-up material remains too sub-Keplerian to form an RSD. The problem of catastrophic magnetic braking that prevents disk formation in dense cores magnetized to realistic levels remains unresolved. Possible resolutions of this problem are discussed.

  16. Physical Model Development and Benchmarking for MHD Flows in Blanket Design

    SciTech Connect

    Ramakanth Munipalli; P.-Y.Huang; C.Chandler; C.Rowell; M.-J.Ni; N.Morley; S.Smolentsev; M.Abdou

    2008-06-05

    An advanced simulation environment to model incompressible MHD flows relevant to blanket conditions in fusion reactors has been developed at HyPerComp in research collaboration with TEXCEL. The goals of this phase-II project are two-fold: The first is the incorporation of crucial physical phenomena such as induced magnetic field modeling, and extending the capabilities beyond fluid flow prediction to model heat transfer with natural convection and mass transfer including tritium transport and permeation. The second is the design of a sequence of benchmark tests to establish code competence for several classes of physical phenomena in isolation as well as in select (termed here as “canonical”,) combinations. No previous attempts to develop such a comprehensive MHD modeling capability exist in the literature, and this study represents essentially uncharted territory. During the course of this Phase-II project, a significant breakthrough was achieved in modeling liquid metal flows at high Hartmann numbers. We developed a unique mathematical technique to accurately compute the fluid flow in complex geometries at extremely high Hartmann numbers (10,000 and greater), thus extending the state of the art of liquid metal MHD modeling relevant to fusion reactors at the present time. These developments have been published in noted international journals. A sequence of theoretical and experimental results was used to verify and validate the results obtained. The code was applied to a complete DCLL module simulation study with promising results.

  17. Algorithm and exploratory study of the Hall MHD Rayleigh-Taylor instability.

    SciTech Connect

    Gardiner, Thomas Anthony

    2010-09-01

    This report is concerned with the influence of the Hall term on the nonlinear evolution of the Rayleigh-Taylor (RT) instability. This begins with a review of the magnetohydrodynamic (MHD) equations including the Hall term and the wave modes which are present in the system on time scales short enough that the plasma can be approximated as being stationary. In this limit one obtains what are known as the electron MHD (EMHD) equations which support two characteristic wave modes known as the whistler and Hall drift modes. Each of these modes is considered in some detail in order to draw attention to their key features. This analysis also serves to provide a background for testing the numerical algorithms used in this work. The numerical methods are briefly described and the EMHD solver is then tested for the evolution of whistler and Hall drift modes. These methods are then applied to study the nonlinear evolution of the MHD RT instability with and without the Hall term for two different configurations. The influence of the Hall term on the mixing and bubble growth rate are analyzed.

  18. MHD Model Estimates of the Contribution of Driven, Linear, Non-Plane Wave Dissipation to Chromospheric Heating Using a Complete Electrical Conductivity Tensor

    NASA Astrophysics Data System (ADS)

    Goodman, M. L.

    2008-12-01

    Analytic solutions of an MHD model that includes an anisotropic, inhomogeneous electrical conductivity tensor containing Hall, Pedersen, and Spitzer conductivities are used to compute resistive heating rates as a function of height z from the photosphere to the lower corona due to dissipation of driven, linear, non- plane waves. The background state of the atmosphere is assumed to be an FAL atmosphere. This state is linearly perturbed by a harmonic perturbation of frequency ν. The height dependence of the perturbation in the presence of the inhomogeneous background state is determined by solving the MHD equations given the harmonic, horizontal, driving magnetic field Bx1 at the photosphere, the constant vertical magnetic field Bz, and the magnetic field strength Bcond(z) that enters the electrical conductivity tensor. The variation of the heating rates per unit volume and mass with ν, Bx1, and Bcond(0) are determined. The heating rates are found to be ∝ Bcond(0)2 Bx12, and to increase with ν. The Pedersen resistivity is ∝ Bcond(0)2. It is several orders of magnitude greater than the Spitzer resistivity in the chromosphere, and determines the rate of heating by Pedersen current dissipation in the chromosphere. The Pedersen current is essentially a proton current in the chromosphere. The onset of Pedersen current dissipation rates large enough to balance the net radiative loss from the chromosphere occurs near the height of the FAL temperature minimum, and is triggered by the product of the electron and proton magnetizations first exceeding unity. The magnetizations and heating rate increase rapidly with height beginning near the temperature minimum. For the special case of Bz = 200 G, Bx1=140 G, and 400 ≤ Bcond(0) ≤ 1500 G the driver frequency for which the period averaged chromospheric heating flux FCh = 5 × 106 ergs-cm-2-sec-1 has the corresponding range of 91 ≥ ν ≥ 25 mHz. Larger magnetic field strengths correspond to lower frequencies for a

  19. A heuristic model for MRI turbulent stresses in Hall MHD

    NASA Astrophysics Data System (ADS)

    Lingam, Manasvi; Bhattacharjee, Amitava

    2016-07-01

    Although the Shakura-Sunyaev α viscosity prescription has been highly successful in characterizing myriad astrophysical environments, it has proven to be partly inadequate in modelling turbulent stresses driven by the magnetorotational instability (MRI). Hence, we adopt the approach employed by Ogilvie, but in the context of Hall magnetohydrodynamics (MHD), to study MRI turbulence. We utilize the exact evolution equations for the stresses, and the non-linear terms are closed through the invocation of dimensional analysis and physical considerations. We demonstrate that the inclusion of the Hall term leads to non-trivial results, including the modification of the Reynolds and Maxwell stresses, as well as the (asymptotic) non-equipartition between the kinetic and magnetic energies; the latter issue is also addressed via the analysis of non-linear waves. The asymptotic ratio of the kinetic to magnetic energies is shown to be independent of the choice of initial conditions, but it is governed by the Hall parameter. We contrast our model with an altered version of the Kazantsev prescription from small-scale dynamo theory, and the Hall term does not generally contribute in the latter approach, illustrating the limitations of this formalism. We indicate potential astrophysical applications of our model, including the solar wind where a lack of equipartition has been observed.

  20. Characterizing Pluto's plasma environment through multifluid MHD modelling

    NASA Astrophysics Data System (ADS)

    Hale, J. M.; Paty, C. S.

    2013-12-01

    We will report on preliminary results from simulations of the Hadean magnetosphere using a refined version of the global multifluid MHD model which has been successfully used to simulate numerous planetary systems, including Ganymede [Paty et al., 2008], Pluto [Harnett et al., 2005], Saturn [Kidder at al., 2012], and Titan [Snowden et al., 2011a,b], among others. This initial study focuses on exploring the exospheric and solar wind parameter space local to Pluto. We explore multiple system geometries including a simulation in which Pluto has no ionosphere, as appears to be the case due to freezing when Pluto resides at apoapsis, as well as several scenarios with different ionospheric and exospheric densities. Ionospheric densities are based on chemical modeling reported in Krasnopolsky and Cruikshank [1999] and solar wind conditions are based on system geometry at periapsis, apoapsis, and at the time of the New Horizons system flyby. We examine the role of the ionosphere and exosphere in determining the location and structure of the bow shock, as well as characterizing the impact of the variability of solar wind pressure and magnetic field throughout Pluto's orbit. This work supports the characterization of the magnetospheric environment of the Pluto system in preparation for the New Horizons encounter in 2015.

  1. Comparing MHD simulations of RFP plasmas to RELAX experiments

    NASA Astrophysics Data System (ADS)

    McCollam, K. J.; den Hartog, D. J.; Jacobson, C. M.; Sauppe, J. P.; Masamune, S.; Sanpei, A.

    2015-11-01

    Standard reversed-field pinch (RFP) plasmas provide a nonlinear dynamical system as a validation domain for numerical MHD simulation codes, which can be applied to general toroidal confinement scenarios including tokamaks. Using the NIMROD code, we calculate linear stability and simulate the nonlinear evolution of plasmas similar to those in the RELAX RFP experiment, whose relatively modest Lundquist numbers of order 104 make the simulations tractable given present computing resources. The chosen RELAX cases cover a broad range of RFP reversal parameters and have also been previously simulated with the MIPS code (N. Mizuguchi et al., TH/P3-26, IAEA FEC, 2012). Experimental diagnostics that can be used for validation purposes include Thomson scattering for electron temperature, interferometry for electron density, SXR imaging, and external and internal magnetic probes. RELAX's small aspect ratio (~ 2) motivates a comparison study using toroidal and cylindrical geometries in NIMROD. This work is supported by the U.S. DOE and NSF and by the Japan Society for the Promotion of Science.

  2. Mefloquine-oxazolidine derivatives, derived from mefloquine and arenecarbaldehydes: In vitro activity including against the multidrug-resistant tuberculosis strain T113.

    PubMed

    Gonçalves, Raoni S B; Kaiser, Carlos R; Lourenço, Maria C S; Bezerra, Flavio A F M; de Souza, Marcus V N; Wardell, James L; Wardell, Solange M S V; Henriques, Maria das Graças M de O; Costa, Thadeu

    2012-01-01

    Ten new mefloquine-oxazolidine derivatives, 4-[(1S,8aR)-3-(aryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline (1: aryl=substituted phenyl) and 4-[(1S,8aR)-3-(heteroaryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline [2: heteroaryl=5-nitrothien-2-yl (2a); 5-nitrofuran-2-yl (2b) and 4H-imidazol-2-yl) (2c)], have been synthesized and evaluated against Mycobacterium tuberculosis. Compounds 1f (aryl=3-ethoxyphenyl), 1g (Ar=3,4,5-(MeO)(3)-C(6)H(2)) and 2c were slightly more active than mefloquine (MIC=33μM) with MICs=24.5, 22.5 and 27.4, respectively, whereas compounds 1e (aryl=3,4-(MeO)(2)-C(6)H(3)) and 2a (MICs=11.9 and 12.1μM, respectively) were ca. 2.7 times more active than mefloquine, with a better tuberculostatic activity than the first line tuberculostatic agent ethambutol (MIC=15.9). The compounds were also assayed against the MDR strain T113 and the same MICs were observed. Thus the new derivatives have advantages over such anti-TB drugs as isoniazid, rifampicin, ethambutol and ofloxacin, for which this strain is resistant. The most active compounds were not cytotoxic to Murine Macrophages Cells in a concentration near their MIC values.

  3. In Planta Expression Screens of Phytophthora infestans RXLR Effectors Reveal Diverse Phenotypes, Including Activation of the Solanum bulbocastanum Disease Resistance Protein Rpi-blb2[W

    PubMed Central

    Oh, Sang-Keun; Young, Carolyn; Lee, Minkyoung; Oliva, Ricardo; Bozkurt, Tolga O.; Cano, Liliana M.; Win, Joe; Bos, Jorunn I.B.; Liu, Hsin-Yin; van Damme, Mireille; Morgan, William; Choi, Doil; Van der Vossen, Edwin A.G.; Vleeshouwers, Vivianne G.A.A.; Kamoun, Sophien

    2009-01-01

    The Irish potato famine pathogen Phytophthora infestans is predicted to secrete hundreds of effector proteins. To address the challenge of assigning biological functions to computationally predicted effector genes, we combined allele mining with high-throughput in planta expression. We developed a library of 62 infection-ready P. infestans RXLR effector clones, obtained using primer pairs corresponding to 32 genes and assigned activities to several of these genes. This approach revealed that 16 of the 62 examined effectors cause phenotypes when expressed inside plant cells. Besides the well-studied AVR3a effector, two additional effectors, PexRD8 and PexRD3645-1, suppressed the hypersensitive cell death triggered by the elicitin INF1, another secreted protein of P. infestans. One effector, PexRD2, promoted cell death in Nicotiana benthamiana and other solanaceous plants. Finally, two families of effectors induced hypersensitive cell death specifically in the presence of the Solanum bulbocastanum late blight resistance genes Rpi-blb1 and Rpi-blb2, thereby exhibiting the activities expected for Avrblb1 and Avrblb2. The AVRblb2 family was then studied in more detail and found to be highly variable and under diversifying selection in P. infestans. Structure-function experiments indicated that a 34–amino acid region in the C-terminal half of AVRblb2 is sufficient for triggering Rpi-blb2 hypersensitivity and that a single positively selected AVRblb2 residue is critical for recognition by Rpi-blb2. PMID:19794118

  4. The Biermann Catastrophe in Numerical MHD

    NASA Astrophysics Data System (ADS)

    Graziani, Carlo; Tzeferacos, Petros; Lee, Dongwook; Weide, Klaus; Lamb, Donald; Fatenejad, Milad; Miller, Joshua

    2014-10-01

    The Biermann Battery (BB) effect is widely invoked as a mechanism to generate cosmic magnetic fields from unmagnetized plasmas. The BB effect, which relies on large, non-aligned gradients of electron density and pressure, is expected to function most efficiently at shocks, where such gradients are largest. Simulations of cosmic magnetogenesis have accordingly relied on shocks to enhance the BB effect. What went unnoticed until recently is the fact that straightforward algorithmic implementations of the BB effect in MHD codes break down precisely at hydrodynamic discontinuities such as shocks - where the BB effect is of greatest interest - yielding results that fail to converge with resolution. We discuss this breakdown, show its origin, and present an alternative algorithm that gives finite and convergent results. We demonstrate convergence using an implementation of the algorithm within the FLASH code, and verify that the algorithm yields physically sensible results at shocks. We discuss novel - and physically observable - effects that attend the BB effect at shocks. This work was supported in part at the University of Chicago by DOE NNSA ASC.

  5. MHD air preheaters: Results of thermomechanical tests

    SciTech Connect

    Valente, T. )

    1994-12-01

    The thermomechanical tests conducted on four different high-purity periclase magnesia-fired brick were used to select suitable refractory material for the design of a regenerative heat exchanger (Cowper type) for an open-cycle indirect preheating, MHD pilot plant. Tests were conducted under the most severe temperature condition allowable in standard test equipment. The choice among the refractories were made supposing that the ranking established with these tests does not change for higher temperatures (up to 1,900 C). Refractory material M1 exhibited the best behavior. The reported values can be used for the preliminary design of the heat exchanger, using the appropriate safety coefficient. The effective behavior of the materials can be completely understood only with experimental data obtained by the effective operation condition, because size and shape of the material strongly affect the service behavior. The best test is a pilot plant, using scaled-down criteria. This will overcome the difficulty of the standard test at 1,900 C, caused by test equipment limitations.

  6. Corrosion and arc erosion in MHD channels

    SciTech Connect

    Rosa, R.J. . Dept. of Mechanical Engineering); Pollina, R.J. . Dept. of Mechanical Engineering EG and G Energy Measurements, Inc., Las Vegas, NV )

    1992-08-01

    The problems connected with gas side corrosion for the design of the lA4 (POC) channel hardware are explored and results of gas side wear rate tests in the Textron Mark VII facility are presented. It is shown that the proposed designs meet a 2000 hour lifetime criterion based upon these materials tests. Improvement in cathode lifetime is demonstrated with lower voltage intercathode gaps. The corrosion of these materials is discussed and it is shown how lifetimes are dependent upon gap voltage and average metal temperature. The importance of uniformity of slagging to the durability of the anode wall is demonstrated. The wear mechanism of the anodes in the MHD channel is analyzed. In addition to gas-side corrosion, the results of specific water corrosion tests of sidewall materials are discussed. All of the tests reported here were carried out to confirm the gas-side performance and the manufacturability of anode and sidewall designs and to address questions posed about the durability of tungsten-copper on the waterside. the results of water corrosion tests of the tungsten copper alloy sidewall material are presented to show that with proper control of waterside pH and, if necessary, dissolved oxygen, one can obtain reliable performance with no degradation of heat transfer with this material. The final choice of materials was determined primarily by the outcome of these tests and also by the question of the manufacturability of the prospective designs.

  7. A self-consistent two-dimensional resistive fluid theory of field-aligned potential structures including charge separation and magnetic and velocity shear

    NASA Technical Reports Server (NTRS)

    Hesse, Michael; Birn, Joachim; Schindler, Karl

    1990-01-01

    A self-consistent two-fluid theory that includes the magnetic field and shear patterns is developed to model stationary electrostatic structures with field-aligned potential drops. Shear flow is also included in the theory since this seems to be a prominent feature of the structures of interest. In addition, Ohmic dissipation, a Hall term, and pressure gradients in a generalized Ohm's law, modified for cases without quasi-neutrality, are included. In the analytic theory, the electrostatic force is balanced by field-aligned pressure gradients (i.e., thermal effects in the direction of the magnetic field) and by pressure gradients and magnetic stresses in the perpendicular direction. Within this theory, simple examples of applications are presented to demonstrate the kind of solutions resulting from the model. The results show how the effects of charge separation and shear in the magnetic field and the velocity can be combined to form self-consistent structures such as are found to exist above the aurora, suggested also in association with solar flares.

  8. Feasibility of MHD submarine propulsion. Phase II, MHD propulsion: Testing in a two Tesla test facility

    SciTech Connect

    Doss, E.D.; Sikes, W.C.

    1992-09-01

    This report describes the work performed during Phase 1 and Phase 2 of the collaborative research program established between Argonne National Laboratory (ANL) and Newport News Shipbuilding and Dry Dock Company (NNS). Phase I of the program focused on the development of computer models for Magnetohydrodynamic (MHD) propulsion. Phase 2 focused on the experimental validation of the thruster performance models and the identification, through testing, of any phenomena which may impact the attractiveness of this propulsion system for shipboard applications. The report discusses in detail the work performed in Phase 2 of the program. In Phase 2, a two Tesla test facility was designed, built, and operated. The facility test loop, its components, and their design are presented. The test matrix and its rationale are discussed. Representative experimental results of the test program are presented, and are compared to computer model predictions. In general, the results of the tests and their comparison with the predictions indicate that thephenomena affecting the performance of MHD seawater thrusters are well understood and can be accurately predicted with the developed thruster computer models.

  9. High-order conservative finite difference GLM-MHD schemes for cell-centered MHD

    NASA Astrophysics Data System (ADS)

    Mignone, Andrea; Tzeferacos, Petros; Bodo, Gianluigi

    2010-08-01

    We present and compare third- as well as fifth-order accurate finite difference schemes for the numerical solution of the compressible ideal MHD equations in multiple spatial dimensions. The selected methods lean on four different reconstruction techniques based on recently improved versions of the weighted essentially non-oscillatory (WENO) schemes, monotonicity preserving (MP) schemes as well as slope-limited polynomial reconstruction. The proposed numerical methods are highly accurate in smooth regions of the flow, avoid loss of accuracy in proximity of smooth extrema and provide sharp non-oscillatory transitions at discontinuities. We suggest a numerical formulation based on a cell-centered approach where all of the primary flow variables are discretized at the zone center. The divergence-free condition is enforced by augmenting the MHD equations with a generalized Lagrange multiplier yielding a mixed hyperbolic/parabolic correction, as in Dedner et al. [J. Comput. Phys. 175 (2002) 645-673]. The resulting family of schemes is robust, cost-effective and straightforward to implement. Compared to previous existing approaches, it completely avoids the CPU intensive workload associated with an elliptic divergence cleaning step and the additional complexities required by staggered mesh algorithms. Extensive numerical testing demonstrate the robustness and reliability of the proposed framework for computations involving both smooth and discontinuous features.

  10. Interpreting observations of molecular outflow sources: the MHD shock code mhd_vode

    NASA Astrophysics Data System (ADS)

    Flower, D. R.; Pineau des Forêts, G.

    2015-06-01

    The planar MHD shock code mhd_vode has been developed in order to simulate both continuous (C) type shock waves and jump (J) type shock waves in the interstellar medium. The physical and chemical state of the gas in steady-state may also be computed and used as input to a shock wave model. The code is written principally in FORTRAN 90, although some routines remain in FORTRAN 77. The documented program and its input data are described and provided as supplementary material, and the results of exemplary test runs are presented. Our intention is to enable the interested user to run the code for any sensible parameter set and to comprehend the results. With applications to molecular outflow sources in mind, we have computed, and are making available as supplementary material, integrated atomic and molecular line intensities for grids of C- and J-type models; these computations are summarized in the Appendices. Appendix tables, a copy of the current version of the code, and of the two model grids are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A63

  11. Computation of resistive instabilities by matched asymptotic expansions

    NASA Astrophysics Data System (ADS)

    Glasser, A. H.; Wang, Z. R.; Park, J.-K.

    2016-11-01

    We present a method for determining the linear resistive magnetohydrodynamic (MHD) stability of an axisymmetric toroidal plasma, based on the method of matched asymptotic expansions. The plasma is partitioned into a set of ideal MHD outer regions, connected through resistive MHD inner regions about singular layers where q =m /n , with m and n toroidal mode numbers, respectively, and q the safety factor. The outer regions satisfy the ideal MHD equations with zero-frequency, which are identical to the Euler-Lagrange equations for minimizing the potential energy δW. The solutions to these equations go to infinity at the singular surfaces. The inner regions satisfy the equations of motion of resistive MHD with a finite eigenvalue, resolving the singularity. Both outer and inner regions are solved numerically by newly developed singular Galerkin methods, using specialized basis functions. These solutions are matched asymptotically, providing a complex dispersion relation which is solved for global eigenvalues and eigenfunctions in full toroidal geometry. The dispersion relation may have multiple complex unstable roots, which are found by advanced root-finding methods. These methods are much faster and more robust than the previous numerical methods. The new methods are applicable to more challenging high-pressure and strongly shaped plasma equilibria and generalizable to more realistic inner region dynamics. In the thermonuclear regime, where the outer and inner regions overlap, they are also much faster and more accurate than the straight-through methods, which treat the resistive MHD equations in the whole plasma volume.

  12. Dependence of plasma responses to an externally applied perturbation field on MHD oscillation frequency on the J-TEXT tokamak

    NASA Astrophysics Data System (ADS)

    Jin, W.; Ding, Y. H.; Rao, B.; Hu, Q. M.; Jin, X. S.; Wang, N. C.; Zhang, X. Q.; Wang, Z. J.; Y Chen, Z.; Zhuang, G.; the J-TEXT Team

    2013-03-01

    The plasma response to externally applied perturbation fields is investigated on the J-TEXT tokamak using a set of static resonant magnetic perturbation (SRMP) coils. Several different experimental results are obtained including partial or complete suppression of the existing m/n = 2/1 tearing mode, mode locking or non-uniform magnetohydrodynamic (MHD) oscillations. These results depend sensitively on the tearing mode frequency and the amplitude of the perturbation field. It is found that mode locking is most likely to happen at a lower rotation frequency (< ˜5 kHz) and the threshold for mode locking has a linear relation with MHD frequency. However, complete suppression of the tearing mode happens in a region where the MHD frequencies are higher (˜6 kHz). The experimental observations are explained by numerical simulations based on reduced MHD equations. The error field contributes to an offset between the mode-locking thresholds for the two opposite spatial phases of the SRMP, through which the intrinsic error field of J-TEXT can be estimated.

  13. Hall-MHD and PIC Modeling of the Conduction-to-Opening Transition in a Plasma Opening Switch

    NASA Astrophysics Data System (ADS)

    Schumer, J. W.; SwanekampDdagger, S. B.; Ottinger, P. F.; Commisso, R. J.; Weber, B. V.

    1998-11-01

    Utilizing the fast opening characteristics of a plasma opening switch (POS), inductive energy storage devices can generate short-duration high-power pulses (<0.1 μ s, >1 TW) with current rise-times on the order of 10 ns. Plasma redistribution and thinning during the POS conduction phase can be modeled adequately with MHD methods. By including the Hall term in Ohm's Law, MHD methods can simulate plasmas with density gradient scale lengths between c/ω_pe < Ln < c/ω_pi. However, the neglect of electron inertia (c/ω_pe) and space-charge separation (λ_De) by single-fluid theory eventually becomes invalid in small gap regions that form during POS opening. PIC methods are well-suited for low-density plasmas, but are numerically taxed by high-density POS regions. An interface converts MHD (Mach2) output into PIC (Magic) input suitable for validating various transition criteria through comparison of current and density distributions from both methods. We will discuss recent progress in interfacing Hall-MHD and PIC simulations. Work supported by Defense Special Weapons Agency. ^ NRL-NRC Research Associate. hspace0.25in ^ JAYCOR, Vienna, VA 22102.

  14. MHD Modeling of Coronal Loops: the Transition Region Throat

    NASA Technical Reports Server (NTRS)

    Guarrasi, M.; Reale, F.; Orlando, S.; Mignone, A.; Klimchuk, J. A.

    2014-01-01

    Context. The expansion of coronal loops in the transition region may considerably influence the diagnostics of the plasma emission measure. The cross-sectional area of the loops is expected to depend on the temperature and pressure, and might be sensitive to the heating rate. Aims. The approach here is to study the area response to slow changes in the coronal heating rate, and check the current interpretation in terms of steady heating models. Methods. We study the area response with a time-dependent 2D magnetohydrodynamic (MHD) loop model, including the description of the expanding magnetic field, coronal heating and losses by thermal conduction, and radiation from optically thin plasma. We run a simulation for a loop 50 Mm long and quasi-statically heated to about 4 millikelvin. Results. We find that the area can change substantially with the quasi-steady heating rate, e.g., by approx. 40% at 0.5 millikelvin as the loop temperature varies between 1 millikelvin and 4 millikelvin, and, therefore, affects the interpretation of the differential emission measure vs. temperature (DEM(T)) curves.

  15. Spectroscopic measurement of the MHD dynamo in the MST reversed field pinch

    SciTech Connect

    Chapman, James Tharp

    1998-09-01

    The author has directly observed the coupling of ion velocity fluctuations and magnetic field fluctuations to produce an MHD dynamo electric field in the interior of the MST reversed field pinch. Chord averaged ion velocity fluctuations were measured with a fast spectroscopic diagnostic which collects line radiation from intrinsic carbon impurities simultaneously along two lines of sight. The chords employed for the measurements resolved long wavelength velocity fluctuations of several km/s at 8-20 kHz as tiny, fast Doppler shifts in the emitted line profile. During discrete dynamo events the velocity fluctuations, like the magnetic fluctuations, increase dramatically. The toroidal and poloidal chords with impact parameters of 0.3 a and 0.6 a respectively, resolved fluctuation wavenumbers with resonance surfaces near or along the lines of sight indicating a radial velocity fluctuation width for each mode which spans only a fraction of the plasma radius. The phase between the measured toroidal velocity fluctuations and the magnetic fluctuations matches the predictions of resistive MHD while the poloidal velocity fluctuations exhibit a phase consistent with the superposition of MHD effects and the advection of a mean flow gradient past the poloidal line of sight. Radial velocity fluctuations resolved by a chord through the center of the plasma were small compared to the poloidal and toroidal fluctuations and exhibited low coherence with the magnetic fluctuations. The ensembled nonlinear product of the ion velocity fluctuations and fluctuations in the magnetic field indicates a substantial dynamo electric field which peaks during the periods of spontaneous flux generation.

  16. THE BEHAVIOR OF TRANSVERSE WAVES IN NONUNIFORM SOLAR FLUX TUBES. I. COMPARISON OF IDEAL AND RESISTIVE RESULTS

    SciTech Connect

    Soler, Roberto; Terradas, Jaume; Oliver, Ramón; Goossens, Marcel

    2013-11-10

    Magnetohydrodynamic (MHD) waves are ubiquitously observed in the solar atmosphere. Kink waves are a type of transverse MHD waves in magnetic flux tubes that are damped due to resonant absorption. The theoretical study of kink MHD waves in solar flux tubes is usually based on the simplification that the transverse variation of density is confined to a nonuniform layer much thinner than the radius of the tube, i.e., the so-called thin boundary approximation. Here, we develop a general analytic method to compute the dispersion relation and the eigenfunctions of ideal MHD waves in pressureless flux tubes with transversely nonuniform layers of arbitrary thickness. Results for kink waves are produced and compared with fully numerical resistive MHD eigenvalue computations in the limit of small resistivity. We find that the frequency and resonant damping rate are the same in both ideal and resistive cases. The actual results for thick nonuniform layers deviate from the behavior predicted in the thin boundary approximation and strongly depend on the shape of the nonuniform layer. The eigenfunctions in ideal MHD are very different from those in resistive MHD. The ideal eigenfunctions display a global character regardless of the thickness of the nonuniform layer, while the resistive eigenfunctions are localized around the resonance and are indistinguishable from those of ordinary resistive Alfvén modes. Consequently, the spatial distribution of wave energy in the ideal and resistive cases is dramatically different. This poses a fundamental theoretical problem with clear observational consequences.

  17. Transport in EHD flows distinct from HD and MHD flows

    NASA Astrophysics Data System (ADS)

    Kikuchi, H.

    2003-04-01

    EHD flows are typically composed of a charged (positively or negatively) fluid, though not all, that may be an electron fluid, an ion fluid or a dust fluid for a single fluid, or their mixtures for multi-component fluids in contrast to nonionized HD or plasma MHD flows. Electric or ponderomotive forces are newly exerted on EHD flows in addition to mechanical, viscous, and magnetic forces on HD and MHD flows. Accordingly, EHD flows hold electric pressure in addition to gas or plasma and magnetic pressure in HD and MHD flows. EHD flows hold space charge and displacement currents and are regarded as a dielectric or semiconducting fluid in contrast to nonionized HD flows or conducting plasma MHD flows. EHD flows are governed by a new equation of electric field transport in addition to fluid vortex transport (HD) and magnetic field transport (MHD), though their equations have to be supplemented by additional terms involving effects of space charge and electric fields, and are characterized by a new electric Reynolds number, R_E with spatial and temporal factors in addition to the fluid Reynolds number, R (spatial) and the magnetic Reynolds number, R_M (spatial) for HD and MHD flows. When R_E >> 1, however, the equation of electric field transport for EHD flows is reduced to the so-called Kelvin-Helmholtz equation just like equations of fluid vortex and magnetic field transport for R >> 1 for HD flows and R_M >> 1 for MHD flows. Accordingly, the EHD relation, H^* = H + v × .D ≈ 0 holds, analogous to the so-called MHD relation, E^* = E + v ×.B ≈ 0. In EHD flows, electric cusp or electrically neutral point can be formed as a bifurcation point of equipotential line or surface, analogous to a stagnation point in HD flows and magnetic cusp or separatrix in MHD flows. Accordingly, electric reconnection or space-charge related electric field line merging with particle acceleration or ionization due to critical velocity effects is possible in EHD flows, analogous to fluid

  18. Numerical MHD Simulation of the Coupled Evolution of Plasma and Magnetic Field in the Solar Chromosphere. I. Gradual and Impulsive Energisation

    NASA Astrophysics Data System (ADS)

    Alekseeva, L. M.; Kshevetskii, S. P.

    2015-11-01

    The dynamical coupling between solar chromospheric plasma and the magnetic field is investigated by numerically solving a fully self-consistent, two-dimensional initial-value problem for the nonlinear collisional MHD equations including electric resistivity, thermal conduction, and, in some cases, gas-dynamic viscosity. The processes in the contact zone between two horizontal magnetic fields of opposite polarities are considered. The plasma is assumed to be initially motionless and to have a temperature of 50,000 K uniform throughout the plasma volume; the characteristic magnetic field corresponds to a plasma β≳ 1. In a physical time interval of 17 seconds typically covered by a computational run, the plasma temperature gradually increases by a factor of two to three. Against this background, an impulsive (in 0.1 seconds or less) increase in the current-aligned plasma velocity occurs at the site of the current-layer thinning (sausage-type deformation, or m=0 pinch instability). This velocity burst can be interpreted physically as an event of suprathermal-proton generation. Further development of the sausage instability results in an increase in the kinetic temperature of the protons to high values, even to those observed in flares. The form of our system of MHD equations indicates that this kind of increase is a property of the exact solution of the system for an appropriate choice of parameters. Magnetic reconnection does not manifest itself in this solution: it would generate flows forbidden by the chosen geometry. Therefore, the pinch-sausage effect can act as an energiser of the upper chromosphere and be an alternative to the magnetic-reconnection process as the producer of flares.

  19. Inductive Evolution and MHD in Local Helicity Injection Discharges on Pegasus

    NASA Astrophysics Data System (ADS)

    Barr, Jayson L.

    Local Helicity Injection (LHI) is a promising non-solenoidal startup technique being investigated on the Pegasus ST. Quantifying the current drive available from LHI is important for projecting to larger devices. A lumped-parameter circuit model for LHI startup has been developed for interpretive analysis of LHI plasmas on Pegasus and a tool for projection. The model recreates I p(t) of outboard LHI discharges with varied shape evolution and LHI drive within +/-15 kA with simplistic assumed plasma resistivity. Outboard LHI plasmas are initialized on the low-field-side and expand to lower aspect ratio (A) and full size. At their initially small, high- A shape the injectors are most effective, but a Taylor relaxation current limit prevents Ip growth. As the plasma expands, the Taylor limit rises, but the injectors become less effective. However, the change in geometry induces large inductive voltages that add significant current drive. Plasma inductance models [38,60] have been re-calibrated to quantify these inductive effects for ultralow-A geometries. The majority ( 80%) of current drive in experiment is provided by the inductive effects from the shape evolution, with peak values as high as 6+ V. The available LHI drive typically falls to less than 0.5 V by the time the plasma reaches full size. Large (b/Bt 1--3 %), n=1 magnetic fluctuations are a signature of LHI plasmas. 3-D, resistive MHD simulations [68,69] predict this activity to be the result of motion and large-scale reconnection events of the injected current, and predict the reconnection to be an underlying method of current drive. Magnetic measurements are consistent with the injected current acting as a current stream line-tied to the injectors and undergoing an elliptical motion in the plasma edge on the low-field-side. This is likely the result of kink and magnetic island coalescence instabilities of the injected current, in partial agreement with simulation. Indirect evidence for the occurrence of

  20. Linear and Nonlinear MHD Wave Processes in Plasmas. Final Report

    SciTech Connect

    Tataronis, J. A.

    2004-06-01

    This program treats theoretically low frequency linear and nonlinear wave processes in magnetized plasmas. A primary objective has been to evaluate the effectiveness of MHD waves to heat plasma and drive current in toroidal configurations. The research covers the following topics: (1) the existence and properties of the MHD continua in plasma equilibria without spatial symmetry; (2) low frequency nonresonant current drive and nonlinear Alfven wave effects; and (3) nonlinear electron acceleration by rf and random plasma waves. Results have contributed to the fundamental knowledge base of MHD activity in symmetric and asymmetric toroidal plasmas. Among the accomplishments of this research effort, the following are highlighted: Identification of the MHD continuum mode singularities in toroidal geometry. Derivation of a third order ordinary differential equation that governs nonlinear current drive in the singular layers of the Alfvkn continuum modes in axisymmetric toroidal geometry. Bounded solutions of this ODE implies a net average current parallel to the toroidal equilibrium magnetic field. Discovery of a new unstable continuum of the linearized MHD equation in axially periodic circular plasma cylinders with shear and incompressibility. This continuum, which we named “accumulation continuum” and which is related to ballooning modes, arises as discrete unstable eigenfrequency accumulate on the imaginary frequency axis in the limit of large mode numbers. Development of techniques to control nonlinear electron acceleration through the action of multiple coherent and random plasmas waves. Two important elements of this program aye student participation and student training in plasma theory.

  1. Results from a large-scale MHD propulsion experiment

    NASA Astrophysics Data System (ADS)

    Petrick, M.; Libera, J.; Bouillard, J. X.; Pierson, E. S.; Hill, D.

    Magnetohydrodynamic (MHD) thrusters have long been recognized as potentially attractive candidates for ship propulsion because such systems eliminate the conventional rotating drive components. The MHD thruster is essentially an electromagnetic (EM) pump operating in seawater. An electrical current is passed directly through the seawater and interacts with an applied magnetic field; the interaction of the magnetic field and the electrode current in the seawater results in a Lorentz force acting on the water, and the reaction to this force propels the vessel forward. The concept of EM propulsion has been examined periodically during the past 35 years as an alternative method of propulsion for surface ships and submersibles. The conclusions reached in early studies were that MHD thrusters restricted to fields of 2 T (the state-of-the-art at that time) were impractical and very inefficient. With the evolution of superconducting magnet technology, later studies investigated the performance of MHD thrusters with much higher magnetic field strengths and concluded that at higher fields (greater than 6-T) practical MHD propulsion systems appear possible. The feasibility of attaining the requisite higher magnetic fields has increased markedly because of rapid advances in building high-field superconducting magnets and the recent evolution of high-temperature superconductors.

  2. A three-dimensional MHD simulation of the interaction of the solar wind with Comet Halley

    NASA Technical Reports Server (NTRS)

    Ogino, Tatsuki; Walker, Raymond J.; Ashour-Abdalla, Maha

    1988-01-01

    The interaction between the solar wind and cometary plasmas is simulated using a three-dimensional time-dependent MHD simulation model, and the results are compared with the recent satellite observations of Comet Halley. The model, which includes cometary mass loading, reproduces many of the features observed by the Suisei probe and the Giottot, including the weak bow shock, the enhancement of the magnetic field in front of the contact surface, and the plasma temperature increase across the bow shock (while it decreased near the comet).

  3. Key contributions in MHD power generation. Quarterly technical progress report, September 1, 1979-November 30, 1979

    SciTech Connect

    Louis, J F

    1980-03-01

    Separate entries were made in the data base for the four tasks which include: (1) investigation of electrical behavior in the vicinity of electrode and insulating walls; (2) studies of critical performance issues in the development of combustion disk generators; (3) development and testing of electrode modules, including studies of insulator properties; and (4) determination of coal combustion kinetics and ash behavior relevant to two-stage MHD combustors, and investigation of the mixing and flow aerodynamics of a high swirl geometry second stage. (WHK)

  4. Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics

    DOE PAGES

    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

  5. Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics

    SciTech Connect

    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.

  6. Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics

    SciTech Connect

    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.

  7. Toward textbook multigrid efficiency for fully implicit resistive magnetohydrodynamics

    SciTech Connect

    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.

  8. Evaluating the Importance of Outflow Velocity at the MHD Inner Boundary

    NASA Astrophysics Data System (ADS)

    Welling, D. T.; Liemohn, M. W.; Toth, G.; Glocer, A.

    2013-12-01

    Including an ionospheric source of magnetospheric plasma in global magnetohydrodynamic models (MHD) is an exercise in setting inner boundary mass density and radial velocity. Recently, in order to account for the complex processes that accelerate plasmas up from ionospheric altitudes to MHD inner boundary altitudes (typically 2.5 to 3 Earth Radii), empirical and first-principles-based models have been developed to set inner boundary conditions in a dynamic and activity-dependent manner. However, such measures are not necessary to achieve outflowing fluences of the order observed by various spacecraft. Spatially and temporally constant boundary conditions, even with zero radial velocity, have been shown to produce dynamic outflow patterns and supply the bulk of magnetospheric plasma. Noteworthy of this approach is the inherent assumption that no acceleration has occurred between the ionosphere and the inner boundary, that is, the ionosphere is simply a mass reservoir. This assumption is contrary to our understanding of the magnetosphere-ionosphere system, yet the net result - outflowing heavy and light ions that populate the rest of geospace - is similar to that when a more realistic outflow specification is applied. The implication is that radial velocity matters little when supplying outflow to global MHD models. This paper investigates the importance of radial velocity at the inner boundary of MHD codes in driving ionospheric outflows into the greater domain. Multi-fluid BATS-R-US is used to simulate an idealized storm, first using zero radial velocity at the inner boundary, then non-zero constant values, and finally with spatially and temporally dynamic values driven by the Polar Wind Outflow Model (PWOM), which sets radial velocity and number density based on physics-based modeling of gap region populations. The results, in terms of total fluence, spatial outflowing flux patterns, and overall magnetospheric response, are compared to investigate how the

  9. Interstellar MHD Turbulence and Star Formation

    NASA Astrophysics Data System (ADS)

    Vázquez-Semadeni, Enrique

    This chapter reviews the nature of turbulence in the Galactic interstellar medium (ISM) and its connections to the star formation (SF) process. The ISM is turbulent, magnetized, self-gravitating, and is subject to heating and cooling processes that control its thermodynamic behavior, causing it to behave approximately isobarically, in spite of spanning several orders of magnitude in density and temperature. The turbulence in the warm and hot ionized components of the ISM appears to be trans- or subsonic, and thus to behave nearly incompressibly. However, the neutral warm and cold components are highly compressible, as a consequence of both thermal instability (TI) in the atomic gas and of moderately-to-strongly supersonic motions in the roughly isothermal cold atomic and molecular components. Within this context, we discuss: (1) the production and statistical distribution of turbulent density fluctuations in both isothermal and polytropic media; (2) the nature of the clumps produced by TI, noting that, contrary to classical ideas, they in general accrete mass from their environment in spite of exhibiting sharp discontinuities at their boundaries; (3) the density-magnetic field correlation (and, at low densities, lack thereof) in turbulent density fluctuations, as a consequence of the superposition of the different wave modes in the turbulent flow; (4) the evolution of the mass-to-magnetic flux ratio (MFR) in density fluctuations as they are built up by dynamic compressions; (5) the formation of cold, dense clouds aided by TI, in both the hydrodynamic (HD) and the magnetohydrodynamic (MHD) cases; (6) the expectation that star-forming molecular clouds are likely to be undergoing global gravitational contraction, rather than being near equilibrium, as generally believed, and (7) the regulation of the star formation rate (SFR) in such gravitationally contracting clouds by stellar feedback which, rather than keeping the clouds from collapsing, evaporates and disperses

  10. Activity of a long-acting echinocandin, CD101, determined using CLSI and EUCAST reference methods, against Candida and Aspergillus spp., including echinocandin- and azole-resistant isolates

    PubMed Central

    Pfaller, Michael A.; Messer, Shawn A.; Rhomberg, Paul R.; Jones, Ronald N.; Castanheira, Mariana

    2016-01-01

    Objectives The objective of this study was to evaluate the in vitro activity of CD101, a novel echinocandin with a long serum elimination half-life, and comparator (anidulafungin and caspofungin) antifungal agents against a collection of Candida and Aspergillus spp. isolates. Methods CD101 and comparator agents were tested against 106 Candida spp. and 67 Aspergillus spp. isolates, including 27 isolates of Candida harbouring fks hotspot mutations and 12 itraconazole non-WT Aspergillus, using CLSI and EUCAST reference susceptibility broth microdilution (BMD) methods. Results Against WT and fks mutant Candida albicans, Candida glabrata and Candida tropicalis, the activity of CD101 [MIC90 = 0.06, 0.12 and 0.03 mg/L, respectively (CLSI method values)] was comparable to that of anidulafungin (MIC90 = 0.03, 0.12 and 0.03 mg/L, respectively) and caspofungin (MIC90 = 0.12, 0.25 and 0.12 mg/L, respectively). WT Candida krusei isolates were very susceptible to CD101 (MIC = 0.06 mg/L). CD101 activity (MIC50/90 = 1/2 mg/L) was comparable to that of anidulafungin (MIC50/90 = 2/2 mg/L) against Candida parapsilosis. CD101 (MIC mode = 0.06 mg/L for C. glabrata) was 2- to 4-fold more active against fks hotspot mutants than caspofungin (MIC mode = 0.5 mg/L). CD101 was active against Aspergillus fumigatus, Aspergillus terreus, Aspergillus niger and Aspergillus flavus (MEC90 range = ≤0.008–0.03 mg/L). The essential agreement between CLSI and EUCAST methods for CD101 was 92.0%–100.0% among Candida spp. and 95.0%–100.0% among Aspergillus spp. Conclusions The activity of CD101 is comparable to that of other members of the echinocandin class for the prevention and treatment of serious fungal infections. Similar results for CD101 activity versus Candida and Aspergillus spp. may be obtained with either CLSI or EUCAST BMD methods. PMID:27287236

  11. Consistent boundary conditions at nonconducting surfaces of planetary bodies: Applications in a new Ganymede MHD model

    NASA Astrophysics Data System (ADS)

    Duling, Stefan; Saur, Joachim; Wicht, Johannes

    2014-06-01

    The interaction of planetary bodies with their surrounding magnetized plasma can often be described with the magnetohydrodynamic (MHD) equations, which are commonly solved by numerical models. For these models it is necessary to define physically correct boundary conditions for the plasma mass and energy density, the plasma velocity, and the magnetic field. Many planetary bodies have surfaces whose electrical conductivity is negligibly small and thus no electric current penetrates their surfaces. Magnetic boundary conditions, which consider that the associated radial electric current at the planetary surface is zero, are difficult to implement because they include the curl of the magnetic field. Here we derive new boundary conditions by a decomposition of the magnetic field in poloidal and toroidal parts. We find that the toroidal part of the magnetic field needs to vanish at the surface of the insulator. For the spherical harmonics coefficients of the poloidal part, we derive a Cauchy boundary condition, which also matches a possible intrinsic field by including its Gauss coefficients. Thus, we can additionally include planetary dynamo fields as well as time-variable induction fields within electrically conductive subsurface layers. We implement the nonconducting boundary condition in the MHD simulation code ZEUS-MP using spherical geometry and provide a numerical implementation in Fortran 90 as supporting information on the JGR website. We apply it to a model for Ganymede's plasma environment. Our model also includes a consistent set of boundary conditions for the other MHD variables density, velocity, and energy. With this model we can describe Galileo spacecraft observations in and around Ganymede's minimagnetosphere very well.

  12. MHD of Aircraft Re-entry: Limits and Perspectives

    NASA Astrophysics Data System (ADS)

    Seller, G.; Capitelli, M.; Longo, S.; Armenise, I.; Bruno, D.

    2005-05-01

    In the present work, starting from classical MHD scheme, based on Maxwell equations, Euler fluid dynamic equations and generalised Ohm law, a critical study of fluid dynamics, electromagnetism, chemical and physical behaviour of plasma is carried out, and then a aircraft re-entry MHD numerical scheme is implemented. This scheme is used for MHD calculations in different conditions, in the range of low magnetic force and intermediate electrical conductivity. Initial imposed magnetic fields are uniform, but also some cases with coil generated magnetic fields are considered. Calculations of magnetic field and induced currents are extended also inside the blunt body. Results show interesting physical and electromagnetic effects. Comparison with other methods shows possible development in keeping into account other physical and chemical effects.

  13. Diagnostic development and support of MHD test facilities

    SciTech Connect

    Not Available

    1990-01-01

    The Diagnostic Instrumentation and Analysis Laboratory (DIAL) at Mississippi State University (MSU) is developing diagnostic instruments for MHD power train data acquisition and for support of MHD component development test facilities. Microprocessor-controlled optical instruments, initially developed for Heat Recovery/Seed Recovery 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 DIAL's computers. Technical support for the diagnostic needs of the national MHD research effort is being provided. DIAL 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. 25 figs., 6 tabs.

  14. MHD of Aircraft Re-entry: Limits and Perspectives

    SciTech Connect

    Seller, G.; Capitelli, M.; Longo, S.; Armenise, I.; Bruno, D.

    2005-05-16

    In the present work, starting from classical MHD scheme, based on Maxwell equations, Euler fluid dynamic equations and generalised Ohm law, a critical study of fluid dynamics, electromagnetism, chemical and physical behaviour of plasma is carried out, and then a aircraft re-entry MHD numerical scheme is implemented. This scheme is used for MHD calculations in different conditions, in the range of low magnetic force and intermediate electrical conductivity. Initial imposed magnetic fields are uniform, but also some cases with coil generated magnetic fields are considered. Calculations of magnetic field and induced currents are extended also inside the blunt body. Results show interesting physical and electromagnetic effects. Comparison with other methods shows possible development in keeping into account other physical and chemical effects.

  15. MHD conversion of solar energy. [space electric power system

    NASA Technical Reports Server (NTRS)

    Lau, C. V.; Decher, R.

    1978-01-01

    Low temperature plasmas wherein an alkali metal vapor is a component are uniquely suited to simultaneously absorb solar radiation by coupling to the resonance lines and produce electrical power by the MHD interaction. This work is an examination of the possibility of developing space power systems which take advantage of concentrated solar power to produce electricity. It is shown that efficient cycles in which expansion work takes place at nearly constant top cycle temperature can be devised. The power density of the solar MHD generator is lower than that of conventional MHD generators because of the relatively high seed concentration required for radiation absorption and the lower flow velocity permitted to avoid total pressure losses due to heating.

  16. Transport and MHD simulations of intrinsic and pellet induced ELMs

    NASA Astrophysics Data System (ADS)

    Kim, Ki Min; Na, Yong-Su; Yi, Sumin; Kim, Hyunseok; Kim, Jin Yong

    2010-11-01

    Verification of ELM mechanism and demonstration of ELM control are important issues in current fusion researches targeting ITER and DEMO. This work investigates the physics and operational characteristics of intrinsic and pellet induced ELMs throughout transport simulations using 1.5 D transport codes (C1.5/ASTRA) and MHD simulations using M3D code. Transport simulations are focused on prediction of the global parameters such as ELM energy loss in the type-I ELMy H-mode discharges with and without pellet pace making to examine an applicability of pellet injection for ELM mitigation in KSTAR and ITER. On the other hand, MHD simulations are conducted to explore the physics of intrinsic and pellet induced ELMs by applying the artificial free energy sources of velocity stream and density perturbations on the marginally stable equilibrium, respectively. Similarities and differences of triggering phenomena between intrinsic and pellet induced ELMs are discussed from the MHD approach.

  17. Applying MHD technology to the continuous casting of steel slab

    NASA Astrophysics Data System (ADS)

    Takeuchi, Eiichi

    1995-05-01

    The application of magnetohydrodynamics (MHD) in the continuous casting process started with the electromagnetic stirring of the stand pool with a traveling magnetic field. It has now advanced to the electromagnetic stirring of molten steel in the mold and the control of molten steel flow by an in-mold direct current magnetic field brake. These applied MHD techniques are designed to further improve the continuous casting process capability. They improve the surface quality of cast steel by homogenizing the meniscus temperature, stabilizing initial solidification, and cleaning the surface layer. They also improve the internal quality of cast steel by preventing inclusions from penetrating deep into the pool and promoting the flotation of argon bubbles. Applied MHD technology is still advancing in scope and methods in addition to the improvement of conventional continuously cast slab qualities. The continuous casting of bimetallic slab by suppressing mixing in the pool is one example of this progress.

  18. Modeling resistive wall modes and disruptive instabilities with M3D-C1

    NASA Astrophysics Data System (ADS)

    Ferraro, Nm; Jardin, Sc; Pfefferle, D.

    2016-10-01

    Disruptive instabilities pose a significant challenge to the tokamak approach to magnetic fusion energy, and must be reliably avoided in a successful reactor. These instabilities generally involve rapid, global changes to the magnetic field, and electromagnetic interaction with surrounding conducting structures. Here we apply the extended-MHD code M3D-C1 to calculate the stability and evolution of disruptive modes, including their interaction with external conducting structures. The M3D-C1 model includes the effects of resistivity, equilibrium rotation, and resistive walls of arbitrary thickness, each of which may play important roles in the stability and evolution of disruptive modes. The strong stabilizing effect of rotation on resistive wall modes is explored and compared with analytic theory. The nonlinear evolution of vertical displacement events is also considered, including the evolution of non-axisymmetric instabilities that may arise during the current-quench phase of the disruption. It is found that the non-axisymmetric stability of the plasma during a VDE depends strongly on the thermal history of the plasma. This work is supported by US DOE Grant DE-AC02-09CH11466 and the SciDAC Center for Extended MHD Modeling.

  19. Research and development studies for MHD/coal power flow train components. Technical progress report, 1 September 1979-31 August 1980

    SciTech Connect

    Bloom, M. H.

    1980-01-01

    The aim of this program is to contribute to certain facets of the development of the MHD/coal power system, and particularly the CDIF of DOE with regard to its flow train. Consideration is given specifically to the electrical power take-off, the diagnostic and instrumentation systems, the combustor and MHD channel technology, and electrode alternatives. Within the constraints of the program, high priorities were assigned to the problems of power take-off and the related characteristics of the MHD channel, and to the establishment of a non-intrusive, laser-based diagnostic system. The next priority was given to the combustor modeling and to a significantly improved analysis of particle combustion. Separate abstracts were prepared for nine of the ten papers included. One paper was previously included in the data base. (WHK)

  20. Extension of the MURaM Radiative MHD Code for Coronal Simulations

    NASA Astrophysics Data System (ADS)

    Rempel, M.

    2017-01-01

    We present a new version of the MURaM radiative magnetohydrodynamics (MHD) code that allows for simulations spanning from the upper convection zone into the solar corona. We implement the relevant coronal physics in terms of optically thin radiative loss, field aligned heat conduction, and an equilibrium ionization equation of state. We artificially limit the coronal Alfvén and heat conduction speeds to computationally manageable values using an approximation to semi-relativistic MHD with an artificially reduced speed of light (Boris correction). We present example solutions ranging from quiet to active Sun in order to verify the validity of our approach. We quantify the role of numerical diffusivity for the effective coronal heating. We find that the (numerical) magnetic Prandtl number determines the ratio of resistive to viscous heating and that owing to the very large magnetic Prandtl number of the solar corona, heating is expected to happen predominantly through viscous dissipation. We find that reasonable solutions can be obtained with values of the reduced speed of light just marginally larger than the maximum sound speed. Overall this leads to a fully explicit code that can compute the time evolution of the solar corona in response to photospheric driving using numerical time steps not much smaller than 0.1 s. Numerical simulations of the coronal response to flux emergence covering a time span of a few days are well within reach using this approach.

  1. Remarks on Singularities, Dimension and Energy Dissipation for Ideal Hydrodynamics and MHD

    NASA Astrophysics Data System (ADS)

    Caflisch, Russel E.; Klapper, Isaac; Steele, Gregory

    For weak solutions of the incompressible Euler equations, there is energy conservation if the velocity is in the Besov space B3s with s greater than 1/3. B3s consists of functions that are Lip(s) (i.e., Hölder continuous with exponent s) measured in the Lp norm. Here this result is applied to a velocity field that is Lip(α0) except on a set of co-dimension on which it is Lip($agr;1), with uniformity that will be made precise below. We show that the Frisch-Parisi multifractal formalism is valid (at least in one direction) for such a function, and that there is energy conservation if . Analogous conservation results are derived for the equations of incompressible ideal MHD (i.e., zero viscosity and resistivity) for both energy and helicity . In addition, a necessary condition is derived for singularity development in ideal MHD generalizing the Beale-Kato-Majda condition for ideal hydrodynamics.

  2. MHD generator of electrical energy working on the gasification products of lignites

    NASA Astrophysics Data System (ADS)

    Derevianko, V. A.; Slavin, V. S.; Sokolov, V. S.

    1981-03-01

    An investigation is presented of an MHD generator of electrical energy fueled by gasification products of lignite coals using the T-layer effect which eliminates caustic additives. A quasi-one-dimensional theory of linear MHD processes is constructed on the basis of MHD equations; a design of an industrial generator is discussed.

  3. ALEGRA-MHD : version 4.6

    SciTech Connect

    Garasi, Christopher Joseph; Cochrane, Kyle Robert; Mehlhorn, Thomas Alan; Haill, Thomas A.; Summers, Randall M.; Robinson, Allen Conrad

    2005-01-01

    ALEGRA is an arbitrary Lagrangian-Eulerian finite element code that emphasizes large distortion and shock propagation in inviscid fluids and solids. This document describes user options for modeling resistive magnetohydrodynamic, thermal conduction, and radiation emission effects.

  4. The superconducting MHD-propelled ship YAMATO-1

    NASA Technical Reports Server (NTRS)

    Sasakawa, Yohei; Takezawa, Setsuo; Sugawara, Yoshinori; Kyotani, Yoshihiro

    1995-01-01

    In 1985 the Ship & Ocean Foundation (SOF) created a committee under the chairmanship of Mr. Yohei Sasakawa, Former President of the Ship & Ocean Foundation, and began researches into superconducting magnetohydrodynamic (MHD) ship propulsion. In 1989 SOF set to construction of a experimental ship on the basis of theoretical and experimental researches pursued until then. The experimental ship named YAMATO-1 became the world's first superconducting MHD-propelled ship on her trial runs in June 1992. This paper describes the outline of the YAMATO-1 and sea trial test results.

  5. The superconducting MHD-propelled ship YAMATO-1

    NASA Astrophysics Data System (ADS)

    Sasakawa, Yohei; Takezawa, Setsuo; Sugawara, Yoshinori; Kyotani, Yoshihiro

    1995-04-01

    In 1985 the Ship & Ocean Foundation (SOF) created a committee under the chairmanship of Mr. Yohei Sasakawa, Former President of the Ship & Ocean Foundation, and began researches into superconducting magnetohydrodynamic (MHD) ship propulsion. In 1989 SOF set to construction of a experimental ship on the basis of theoretical and experimental researches pursued until then. The experimental ship named YAMATO-1 became the world's first superconducting MHD-propelled ship on her trial runs in June 1992. This paper describes the outline of the YAMATO-1 and sea trial test results.

  6. Characterization of open-cycle coal-fired MHD generators

    NASA Astrophysics Data System (ADS)

    Wormhoudt, J.; Yousefian, V.; Weinberg, M.; Kolb, C.; Martinez-Sanchez, M.; Cheng, W.; Bien, F.; Dvore, D.; Unkel, W.; Stewart, G.

    1980-09-01

    The successful design of full-scale, open-cycle, coal-fired MHD generators for baseload electrical production requires a detailed understanding of the plasma chemical and plasma dynamic characteristics of anticipated combustor and channel fluids. Progress in efforts to model the efficiency of an open-cycle, coal-fired MHD channel based on the characterization of the channel flow as well as laboratory experiments to validate the modeling effort is detailed. In addition, studies related to understanding arcing phenomena in the vicinity of an anode are reported.

  7. Efficient Low Dissipative High Order Schemes for Multiscale MHD Flows

    NASA Technical Reports Server (NTRS)

    Sjoegreen, Bjoern; Yee, Helen C.; Mansour, Nagi (Technical Monitor)

    2002-01-01

    Accurate numerical simulations of complex multiscale compressible viscous flows, especially high speed turbulence combustion and acoustics, demand high order schemes with adaptive numerical dissipation controls. Standard high resolution shock-capturing methods are too dissipative to capture the small scales and/or long-time wave propagations without extreme grid refinements and small time steps. An integrated approach for the control of numerical dissipation in high order schemes for the compressible Euler and Navier-Stokes equations has been developed and verified by the authors and collaborators. These schemes are suitable for the problems in question. Basically, the scheme consists of sixth-order or higher non-dissipative spatial difference operators as the base scheme. To control the amount of numerical dissipation, multiresolution wavelets are used as sensors to adaptively limit the amount and to aid the selection and/or blending of the appropriate types of numerical dissipation to be used. Magnetohydrodynamics (MHD) waves play a key role in drag reduction in highly maneuverable high speed combat aircraft, in space weather forecasting, and in the understanding of the dynamics of the evolution of our solar system and the main sequence stars. Although there exist a few well-studied second and third-order high-resolution shock-capturing schemes for the MHD in the literature, these schemes are too diffusive and not practical for turbulence/combustion MHD flows. On the other hand, extension of higher than third-order high-resolution schemes to the MHD system of equations is not straightforward. Unlike the hydrodynamic equations, the inviscid MHD system is non-strictly hyperbolic with non-convex fluxes. The wave structures and shock types are different from their hydrodynamic counterparts. Many of the non-traditional hydrodynamic shocks are not fully understood. Consequently, reliable and highly accurate numerical schemes for multiscale MHD equations pose a great

  8. Magnetohydrodynamic (MHD) modelling of solar active phenomena via numerical methods

    NASA Technical Reports Server (NTRS)

    Wu, S. T.

    1988-01-01

    Numerical ideal MHD models for the study of solar active phenomena are summarized. Particular attention is given to the following physical phenomena: (1) local heating of a coronal loop in an isothermal and stratified atmosphere, and (2) the coronal dynamic responses due to magnetic field movement. The results suggest that local heating of a magnetic loop will lead to the enhancement of the density of the neighboring loops through MHD wave compression. It is noted that field lines can be pinched off and may form a self-contained magnetized plasma blob that may move outward into interplanetary space.

  9. Evaluation of quinolones for use in detection of determinants of acquired quinolone resistance, including the new transmissible resistance mechanisms qnrA, qnrB, qnrS, and aac(6')Ib-cr, in Escherichia coli and Salmonella enterica and determinations of wild-type distributions.

    PubMed

    Cavaco, L M; Aarestrup, F M

    2009-09-01

    Fluoroquinolone resistance in members of the Enterobacteriaceae family is mostly due to mutations in the quinolone resistance-determining regions of the topoisomerase genes. However, transferable genes encoding quinolone resistance have recently been described. The current methods for susceptibility testing are not adapted to the detection of new resistance determinants, which confer low levels of resistance. The aim of this study was to compare the ability of the screening of the different quinolones by disk diffusion assays and MIC determinations to detect fluoroquinolone resistance. Sixty-nine Escherichia coli strains and 62 Salmonella strains, including strains fully susceptible to quinolones, nalidixic acid-resistant strains, strains with resistance to fluoroquinolones (resistant to nalidixic acid), and strains showing low-level resistance to fluoroquinolones conferred by transferable quinolone resistance genes, including qnrA, qnrB, qnrS, and aac(6')Ib-cr, were selected. Disk diffusion assays and MIC determinations by the agar dilution method were performed, according to CLSI standards, with nalidixic acid, flumequine, oxolinic acid, ciprofloxacin, enrofloxacin, marbofloxacin, norfloxacin, ofloxacin, and levofloxacin. The MIC of levofloxacin was determined by an Etest. The results showed a trimodal distribution of the MICs for both E. coli and Salmonella. The MIC distributions for the isolates varied with the compounds tested. Screening for nalidixic acid resistance by MIC testing or disk diffusion assay was not efficient for the detection of some of the isolates carrying qnr and aac(6')Ib-cr. Transferable resistance genes would best be detected by testing for the MIC of ciprofloxacin or norfloxacin, as testing for the MICs of the other compounds would fail to detect isolates carrying aac(6')Ib-cr because the enzyme produced is able to reduce the activities of these two compounds only due to their chemical structures. In conclusion, screening with nalidixic

  10. Resonant behaviour of MHD waves on magnetic flux tubes. III - Effect of equilibrium flow

    NASA Technical Reports Server (NTRS)

    Goossens, Marcel; Hollweg, Joseph V.; Sakurai, Takashi

    1992-01-01

    The Hollweg et al. (1990) analysis of MHD surface waves in a stationary equilibrium is extended. The conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. (1990) are generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant is recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines and flow along the magnetic field lines. It is shown that the conclusions formulated by Hollweg et al. are still valid for the straight cylindrical case. The effect of curvature is examined.

  11. Dynamics of heavy impurities in non-linear MHD simulations of sawtoothing tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Ahn, Jae-H.; Garbet, X.; Lütjens, H.; Guirlet, R.

    2016-12-01

    The effect of sawteeth on impurity dynamics is studied with the XTOR-2F code. Non-linear full 3D MHD simulations including appropriate fluid equations for impurities in the high collisional regime show that the presence of regular sawtooth crashes affects the impurity behaviour. A spatial non-uniformity of 5 % in post-crash impurity density profiles persists due to 2D structures of impurity density which appear during sawtooth crashes. They are shown to be mainly driven by the \\mathbf{E}× \\mathbf{B} velocity, and are responsible for the sudden impurity transport in the core plasmas.

  12. MHD Modeling of the Interaction of the Solar Wind With Venus

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1996-01-01

    The primary objective of this research program is to improve our understanding of the physical processes occurring in the interaction of the solar wind with Venus. This will be accomplished through the use of numerical solutions of the two- and three-dimensional magnetohydrodynamic (MHD) equations and through comparisons of the computed results with available observations. A large portion of this effort involves the study of processes due to the presence of the magnetic field and the effects of mass loading. Published papers are included in the appendix.

  13. Stability of the Halley cometosheath with resistivity and plasma motion

    NASA Technical Reports Server (NTRS)

    Srivastava, Krishna M.; Tsurutani, Bruce T.; Goldstein, Bruce E.; Sharma, V.

    1993-01-01

    The MHD stability of the cometary inner sheath determined by the balance between the inward Lorentz body force and the outward ion-neutral drag force is investigated by numerically solving the wave equations which include resistivity, plasma motion and plasma pressure with the help of two-point boundary value method. The eigenvalues and the eigenfunctions are obtained numerically by treating the cometary inner sheath as a layer of finite thickness, bounded by the contact surface, that is, the diamagnetic cavity boundary. To gain insight into the problem, certain limiting cases of the wave equations are also discussed. The diamagnetic cavity boundary and the adjacent layer of about 100-km thickness of Comet Halley is found to be unstable. The effects of finite plasma pressure, dissociative recombination, mass loading due to photoionization, resistivity, and plasma motion are found to be stabilizing but are unable to quench the instability completely. Motion of the Halley ionopause has been confirmed by observations.

  14. Integration of Extended MHD and Kinetic Effects in Global Magnetosphere Models

    NASA Astrophysics Data System (ADS)

    Germaschewski, K.; Wang, L.; Maynard, K. R. M.; Raeder, J.; Bhattacharjee, A.

    2015-12-01

    Computational models of Earth's geospace environment are an important tool to investigate the science of the coupled solar-wind -- magnetosphere -- ionosphere system, complementing satellite and ground observations with a global perspective. They are also crucial in understanding and predicting space weather, in particular under extreme conditions. Traditionally, global models have employed the one-fluid MHD approximation, which captures large-scale dynamics quite well. However, in Earth's nearly collisionless plasma environment it breaks down on small scales, where ion and electron dynamics and kinetic effects become important, and greatly change the reconnection dynamics. A number of approaches have recently been taken to advance global modeling, e.g., including multiple ion species, adding Hall physics in a Generalized Ohm's Law, embedding local PIC simulations into a larger fluid domain and also some work on simulating the entire system with hybrid or fully kinetic models, the latter however being to computationally expensive to be run at realistic parameters. We will present an alternate approach, ie., a multi-fluid moment model that is derived rigorously from the Vlasov-Maxwell system. The advantage is that the computational cost remains managable, as we are still solving fluid equations. While the evolution equation for each moment is exact, it depends on the next higher-order moment, so that truncating the hiearchy and closing the system to capture the essential kinetic physics is crucial. We implement 5-moment (density, momentum, scalar pressure) and 10-moment (includes pressure tensor) versions of the model, and use local approximations for the heat flux to close the system. We test these closures by local simulations where we can compare directly to PIC / hybrid codes, and employ them in global simulations using the next-generation OpenGGCM to contrast them to MHD / Hall-MHD results and compare with observations.

  15. Performance enhancement of explosive-driven MHD generators

    SciTech Connect

    Smith, I.R.; Senior, P.; Stewardson, H.R.; Vadher, V.V. . Dept. of Electronic and Electrical Engineering); Novac, B.M. )

    1994-11-01

    The change in the circuit inductance of a pulsed MHD generator as the plasma sheet travels along the electrodes acts to increase the voltage produced in the generator. The paper explains how unconventional electrode arrangements enable this effect to be significantly magnified, thereby bringing about a considerable increase in the output that can be obtained.

  16. Electrical characteristics of a seawater MHD thruster. Final report

    SciTech Connect

    Tempelmeyer, K.E.

    1990-06-01

    There is renewed interest in the application of the magnetohydrodynamic (MHD) propulsion concept to marine propulsion. However, there is almost no experimental information concerning the major physical processes which will occur in a seawater MHD propulsion unit, such as (1) the seawater electrolysis process at operational conditions needed for ship propulsion, (2) the effects of bubble formation on the performance of a seawater thruster and (3) the effectiveness of the MHD interaction in seawater. Small scale tests of an MHD type channel but without an applied magnetic field have been carried out to provide information about the first two of these areas (1) seawater electrolysis and (2) the effect of the H2 bubbles generated during the electrolysis of seawater. Current/voltage characteristics were obtained with different electrode materials for current densities up to 0.3 amp/sq cm. The effect of bubble formation on the channel current has been assessed over a range of operating conditions. Long-duration tests to 100 hrs have been made to provide information on electrode durability and long-term operational problems.

  17. TAE modes and MHD activity in TFTR DT plasmas

    SciTech Connect

    Fredrickson, E.; Batha, S.; Bell, M.

    1995-03-01

    The high power deuterium and tritium experiments on TFTR have produced fusion a parameters similar to those expected on ITER. The achieved {beta}{sub {alpha}}/{beta} and the R{triangledown}{beta}{sub {alpha}} in TFRR D-T shots are 1/2 to 1/3 those predicted in the ITER EDA. Studies of the initial TFTR D-T plasmas find no evidence that the presence of the fast fusion {alpha} population has affected the stability of MHD, with the possible exception of Toroidal Alfven Eigenmodes (TAE`s). The initial TFTR DT plasmas had MHD activity similar to that commonly seen in deuterium plasmas. Operation of TFTR at plasma currents of 2.0--2.5 MA has greatly reduced the deleterious effects of MHD commonly observed at lower currents. Even at these higher currents, the performance of TFTR is limited by {beta}-limit disruptions. The effects of MHD on D-T fusion {alpha}`s was similar to effects observed on other fusion products in D only plasmas.

  18. Three-dimensional analysis of MHD generators and diffusers

    SciTech Connect

    Vanka, S P; Ahluwalia, R K; Doss, E D

    1982-03-01

    The three-dimensional flow and heat transfer phenomena in MHD channels and diffusers are analyzed by solving the governing partial differential equations for flow and electrical fields. The equation set consists of the mass continuity equation, the three momentum equations, the equations for enthalpy, turbulence kinetic energy and its dissipation rate, and the Maxwell equations. This set of coupled equations is solved by the use of a finite-difference calculation procedure. The turbulence is represented by a two-equation model of turbulence in which partial differential equations are solved for the turbulence kinetic energy and its dissipation rate. Calculations have been performed for Faraday and diagonally-connected channels. Specifically, the AEDC (Faraday) and the UTSI (diagonal) channels have been analyzed, and the results are compared with experimental data. The agreement is fairly good for all the measured quantities. The effects of channel loading on the three-dimensional flow characteristics of Faraday and diagonally-connected generators have been also analyzed. A simple argument is presented to show qualitatively the role of MHD body forces in generating axial vorticity and hence secondary flows in the cross-stream. Calculations have also been made to study the flow evolution in MHD diffusers. The calculations show that the velocity overshoots and secondary flows decay along the diffusers length. Plots of velocity, skin friction and pressure recovery are presented to illustrate the flow development in MHD diffusers.

  19. 3D MHD Models of Active Region Loops

    NASA Technical Reports Server (NTRS)

    Ofman, Leon

    2004-01-01

    Present imaging and spectroscopic observations of active region loops allow to determine many physical parameters of the coronal loops, such as the density, temperature, velocity of flows in loops, and the magnetic field. However, due to projection effects many of these parameters remain ambiguous. Three dimensional imaging in EUV by the STEREO spacecraft will help to resolve the projection ambiguities, and the observations could be used to setup 3D MHD models of active region loops to study the dynamics and stability of active regions. Here the results of 3D MHD models of active region loops are presented, and the progress towards more realistic 3D MHD models of active regions. In particular the effects of impulsive events on the excitation of active region loop oscillations, and the generation, propagations and reflection of EIT waves are shown. It is shown how 3D MHD models together with 3D EUV observations can be used as a diagnostic tool for active region loop physical parameters, and to advance the science of the sources of solar coronal activity.

  20. Oxygen-enriched air production for MHD power plants

    NASA Astrophysics Data System (ADS)

    1980-05-01

    An analysis of several of the cryogenic air separation process cycle variations and compression schemes designed to minimize net system power requirements for supplying pressurized, oxygen-enriched air to the combustor of a 2000 MWt (coal input) baseload MHD power plant is presented.

  1. MHD--Developing New Technology to Meet the Energy Crisis

    ERIC Educational Resources Information Center

    Fitch, Sandra S.

    1978-01-01

    Magnetohydrodynamics is a technology that could utilize the nation's most abundant fossil fuel and produce electrical energy more efficiently and cleanly than present-day turbines. A national research and development program is ongoing in Butte, Montana at the Montana Energy and MHD Research and Development Institute (MERDI). (Author/RK)

  2. Modified NASA-Lewis chemical equilibrium code for MHD applications

    NASA Technical Reports Server (NTRS)

    Sacks, R. A.; Geyer, H. K.; Grammel, S. J.; Doss, E. D.

    1979-01-01

    A substantially modified version of the NASA-Lewis Chemical Equilibrium Code was recently developed. The modifications were designed to extend the power and convenience of the Code as a tool for performing combustor analysis for MHD systems studies. The effect of the programming details is described from a user point of view.

  3. MHD Energy Bypass Scramjet Performance with Real Gas Effects

    NASA Technical Reports Server (NTRS)

    Park, Chul; Mehta, Unmeel B.; Bogdanoff, David W.

    2000-01-01

    The theoretical performance of a scramjet propulsion system incorporating an magneto-hydro-dynamic (MHD) energy bypass scheme is calculated. The one-dimensional analysis developed earlier, in which the theoretical performance is calculated neglecting skin friction and using a sudden-freezing approximation for the nozzle flow, is modified to incorporate the method of Van Driest for turbulent skin friction and a finite-rate chemistry calculation in the nozzle. Unlike in the earlier design, in which four ramp compressions occurred in the pitch plane, in the present design the first two ramp compressions occur in the pitch plane and the next two compressions occur in the yaw plane. The results for the simplified design of a spaceliner show that (1) the present design produces higher specific impulses than the earlier design, (2) skin friction substantially reduces thrust and specific impulse, and (3) the specific impulse of the MHD-bypass system is still better than the non-MHD system and typical rocket over a narrow region of flight speeds and design parameters. Results suggest that the energy management with MHD principles offers the possibility of improving the performance of the scramjet. The technical issues needing further studies are identified.

  4. Transition of energy transfer from MHD turbulence to kinetic plasma

    NASA Astrophysics Data System (ADS)

    Yang, Yan; Matthaeus, William; Parashar, Tulasi; Shi, Yipeng; Wan, Minping; Chen, Shiyi

    2016-11-01

    The classical energy cascade scenario is of great importance in explaining the heating of corona and solar wind. One can envision that energy residing in large-scale fluctuations is transported to smaller scales where dissipation occurs and finally drives kinetic processes that absorb the energy flux and energize charged particles. Here we inquire how the cascade operates in a compressible plasma, and how the characteristics of energy transfer vary going from MHD to kinetic scales. When filtering MHD equations, we can get an apparent inertial range over which the conservative energy cascade occurs and the scale locality of energy transfer is similar to the cases of incompressible MHD turbulence. Pervasive shocks not only make a significant difference on energy cascade and magnetic amplification, but can also introduce considerable pressure dilation, a complement of viscous and ohmic dissipation that can trigger an alternative channel of the conversion between kinetic and internal energy. The procedure can also be applied to the Vlasov equation and kinetic simulation, in comparison with MHD turbulence, and is a good candidate to investigate the energy cascade process and the analogous role of the (tensor) pressure dilation in collisionless plasma.

  5. Performance characteristics of an MHD (Magnetohydrodynamic) pilot plant electrostatic precipitator

    NASA Astrophysics Data System (ADS)

    Lindner, J. S.; Jang, P. R.; Okhuysen, W. P.; Holt, J. K.

    In magnetohydrodynamic (MHD) power generation, a seed material, normally K2CO3, is added to enhance the conductivity of the coal-fired gas stream. The plasma is passed through a magnetic field and electricity is produced by the Hall effect. Future large scale MHD facilities are expected to be more efficient than conventional coal-fired power plants not only because of the dc electricity produced but also from increased heat recovery owing to the large (3000 K) combustion temperatures employed. There is; however, a finite cost for the seed material and the resulting K2SO4 particles (SO2 emissions are minimized by combination with seed potassium) must be collected, converted back to K2CO3 or KCO2H, and recycled back to the combustor. The performance characteristics of the MHD electrostatic precipitator (ESP) are therefore, of interest. We describe Mie scattering and electric field measurements on an MHD pilot scale ESP located at the Coal Fire Flow Facility (CFFF) at the University of Tennessee Space Institute. Results are reported for the determination of near-real-time collection efficiencies, the variation of the ESP performance with seed percentage, and initial studies on the extent of particle re-entrainment.

  6. Antibiotic-Resistant Escherichia coli Bacteria, Including Strains with Genes Encoding the Extended-Spectrum Beta-Lactamase and QnrS, in Waterbirds on the Baltic Sea Coast of Poland▿

    PubMed Central

    Literak, Ivan; Dolejska, Monika; Janoszowska, Dagmar; Hrusakova, Jolana; Meissner, Wlodzimierz; Rzyska, Hanna; Bzoma, Szymon; Cizek, Alois

    2010-01-01

    Individual cloacal swabs of mallards (Anas platyrhynchos) and of herring gulls (Larus argentatus), as well as samples of waterbird feces obtained in 2008 and 2009, were cultivated for Escherichia coli. Isolates of E. coli were tested for susceptibilities to 12 antimicrobial agents by the disk diffusion method. Moreover, the samples were subcultivated on MacConkey agar (MCA) containing cefotaxime (2 mg liter−1) to detect E. coli with extended-spectrum beta-lactamase (ESBL) and subsequently on MCA supplemented with ciprofloxacin (0.05 mg liter−1) and MCA with nalidixic acid (20 mg liter−1) to isolate fluoroquinolone-resistant E. coli. PCR was used to detect specific antibiotic resistance genes. We found 9 E. coli isolates producing ESBL with bla genes: blaCTX-M-1 (6 isolates), blaCTX-M-9 plus blaTEM-1b (1 isolate), blaCTX-M-15 plus blaOXA-1 (1 isolate), and blaSHV-12 (1 isolate). In the isolate with blaCTX-M-15, the gene aac(6)-Ib-cr was also detected. The bla genes were harbored by transferable plasmids of the IncN and IncI1 groups. Nine quinolone-resistant E. coli isolates with qnrS genes were found and characterized. The gene qnrS was associated with a Tn3-like transposon on the IncX1 plasmid together with blaTEM-1 in two isolates. The gene qnrS was also harbored by conjugative plasmids of the IncN and IncX2 groups. Even if populations of wild birds are not directly influenced by antibiotic practice, we have demonstrated that antibiotic-resistant E. coli strains, including strains with various ESBL and qnrS genes, are found in the feces of wild birds on the coast of the Baltic Sea in Poland. PMID:20952638

  7. Antibiotic-resistant Escherichia coli bacteria, including strains with genes encoding the extended-spectrum beta-lactamase and QnrS, in waterbirds on the Baltic Sea Coast of Poland.

    PubMed

    Literak, Ivan; Dolejska, Monika; Janoszowska, Dagmar; Hrusakova, Jolana; Meissner, Wlodzimierz; Rzyska, Hanna; Bzoma, Szymon; Cizek, Alois

    2010-12-01

    Individual cloacal swabs of mallards (Anas platyrhynchos) and of herring gulls (Larus argentatus), as well as samples of waterbird feces obtained in 2008 and 2009, were cultivated for Escherichia coli. Isolates of E. coli were tested for susceptibilities to 12 antimicrobial agents by the disk diffusion method. Moreover, the samples were subcultivated on MacConkey agar (MCA) containing cefotaxime (2 mg liter(-1)) to detect E. coli with extended-spectrum beta-lactamase (ESBL) and subsequently on MCA supplemented with ciprofloxacin (0.05 mg liter(-1)) and MCA with nalidixic acid (20 mg liter(-1)) to isolate fluoroquinolone-resistant E. coli. PCR was used to detect specific antibiotic resistance genes. We found 9 E. coli isolates producing ESBL with bla genes: bla(CTX-M-1) (6 isolates), bla(CTX-M-9) plus bla(TEM-1b) (1 isolate), bla(CTX-M-15) plus bla(OXA-1) (1 isolate), and bla(SHV-12) (1 isolate). In the isolate with bla(CTX-M-15), the gene aac(6)-Ib-cr was also detected. The bla genes were harbored by transferable plasmids of the IncN and IncI1 groups. Nine quinolone-resistant E. coli isolates with qnrS genes were found and characterized. The gene qnrS was associated with a Tn3-like transposon on the IncX1 plasmid together with bla(TEM-1) in two isolates. The gene qnrS was also harbored by conjugative plasmids of the IncN and IncX2 groups. Even if populations of wild birds are not directly influenced by antibiotic practice, we have demonstrated that antibiotic-resistant E. coli strains, including strains with various ESBL and qnrS genes, are found in the feces of wild birds on the coast of the Baltic Sea in Poland.

  8. System studies of coal fired-closed cycle MHD for central station power plants

    NASA Technical Reports Server (NTRS)

    Zauderer, B.

    1976-01-01

    This paper presents a discussion of the closed-cycle MHD results obtained in a recent study of various advanced energy-conversion power systems. The direct coal-fired MHD topping-steam bottoming cycle was established as the current choice for central station power generation. Emphasis is placed on the background assumptions and the conclusions that can be drawn from the closed-cycle MHD analysis. It is concluded that closed-cycle MHD has efficiencies comparable to that of open-cycle MHD. Its cost will possibly be slightly higher than that of the open-cycle MHD system. Also, with reasonable fuel escalation assumptions, both systems can produce lower-cost electricity than conventional steam power plants. Suggestions for further work in closed-cycle MHD components and systems are made.

  9. Integration of MHD load models with circuit representations the Z generator.

    SciTech Connect

    Jennings, Christopher A.; Ampleford, David J.; Jones, Brent Manley; McBride, Ryan D.; Bailey, James E.; Jones, Michael C.; Gomez, Matthew Robert.; Cuneo, Michael Edward; Nakhleh, Charles; Stygar, William A.; Savage, Mark Edward; Wagoner, Timothy C.; Moore, James K.

    2013-03-01

    MHD models of imploding loads fielded on the Z accelerator are typically driven by reduced or simplified circuit representations of the generator. The performance of many of the imploding loads is critically dependent on the current and power delivered to them, so may be strongly influenced by the generators response to their implosion. Current losses diagnosed in the transmission lines approaching the load are further known to limit the energy delivery, while exhibiting some load dependence. Through comparing the convolute performance of a wide variety of short pulse Z loads we parameterize a convolute loss resistance applicable between different experiments. We incorporate this, and other current loss terms into a transmission line representation of the Z vacuum section. We then apply this model to study the current delivery to a wide variety of wire array and MagLif style liner loads.

  10. Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment

    SciTech Connect

    V.S. Lukin; S.C. Jardin

    2003-01-09

    Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given.

  11. Investigation of pellet-triggered MHD events in the ASDEX upgrade

    SciTech Connect

    Lang, P. T.; Lackner, K.; Kallenbach, A.; Maraschek, M.; Perez von Thun, C. P.; Suttrop, W.

    2008-09-15

    In order to gain deeper insight into the process of MHD activity triggered by pellets we extended our previous analysis (standard type-I edge localized modes (ELMs)) to type-I ELMs in radiative edge scenarios, type-III ELMs, the quiescent H-mode regime, and core mode activity such as neoclassical tearing modes or snakes. Pellet triggering of mode activity has turned out to be a quite general feature, but only in case of the ELMs can it be unambiguously attributed to prompt local impact by the pellet. For edge plasma conditions characterized by higher resistivity, the growth time of spontaneous ELMs increases while the plasma changes from the type-I into the type-III regime. However, pellet-triggered ELMs retain fast rise times. In the quiescent Hmode, pellets still trigger ELM-like mode activity, but no longer accompanied by a significant release of energy from the plasma.

  12. KSTAR first plasma equilibrium reconstruction and study of global MHD stability control

    NASA Astrophysics Data System (ADS)

    Katsuro-Hopkins, O.; Sabbagh, S. A.; Bialek, J. M.; Park, H. K.; You, K. I.; Lee, S. G.; Bak, J. G.; Yoon, S. W.; Kim, J. H.; Kim, J. Y.; Glasser, A. H.; Lao, L. L.

    2008-11-01

    Korea Superconducting Tokamak Advanced Research, KSTAR, equilibria are computed using EFIT and VALEN based on numerical models and recent experimental data from first plasma operation. A 3-D double-walled vacuum vessel model with port penetrations was used to evaluate the vacuum vessel effective resistance and to simulate and compare to the time evolution of experimental magnetic diagnostic measurements during vacuum poloidal field coil testing and plasma start-up scenarios. KSTAR is designed to produce wall-stabilized high beta equilibria. Ideal MHD stability of toroidal mode number of unity using DCON shows a factor of two improvement in the normalized beta limit over the no-wall beta limit (up to 5) at moderate to low plasma internal inductance. Reaching these high normalized beta levels is possible using passive and active control with classical and advanced state-space based control algorithms at the reasonable power levels.

  13. MHD Technology Transfer, Integration and Review Committee. Fifth semi-annual status report, April 1990--September 1990

    SciTech Connect

    Not Available

    1992-01-01

    This fifth semi-annual status report of the MHD Technology Transfer, Integration, and Review Committee (TTIRC) summarizes activities of the TTIRC during the period April 1990 through September 1990. It includes summaries and minutes of committee meetings, progress summaries of ongoing Proof-of-Concept (POC) contracts, discussions pertaining to technical integration issues in the POC program, and planned activities for the next six months.

  14. MHD Analysis of the Tokamak Edge Pedestal in the Low Collisionality Regime

    NASA Astrophysics Data System (ADS)

    Snyder, P. B.; Wilson, H. R.; Konz, C.

    2005-10-01

    The peeling-ballooning model proposes that intermediate wavelength MHD instabilities are responsible for edge localized modes (ELMs) and impose constraints on the pedestal height. In typical discharges with ELMs, the pedestal goes unstable to coupled peeling-ballooning or pure ballooning modes shortly before an ELM is observed. However, at very low collisionality, the bootstrap current in the pedestal region can be large, even very near the separatrix, and the discharge can be most unstable to current-driven kink/peeling modes, typically at relatively low mode number (n˜,1-10). Recently, interesting ELM-free regimes, including both Quiescent (QH) and Resonant Magnetic Perturbation (RMP) H-mode, have been observed to occur in this low collisionality regime. Here we systematically explore MHD stability in this regime, including the effects of a conducting wall and sheared toroidal flow. We consider the implications for both RMP and QH discharges, including possible connections between the EHO observed in QH mode and low-n kink/peeling modes.

  15. MHD simulation of the evolution of the solar corona around August 1st 2010 using the HMI solar magnetic field data

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Hmi Team

    2010-12-01

    We will report results of the MHD simulation of the solar corona and solar wind using the HMI magnetic field data, especially focusing on a simulated eruption of a coronal streamer that reasonably corresponds to a large-scale coronal eruption event observed on August 1, 2010. The pre-event coronal situation is prepared through the time-relaxation MHD simulation using the synoptic map data of the solar surface magnetic field for a period of the Carrington Rotation 2098. Then, the global magnetic field evolutions from CR 2098 to 2099 are introduced in the simulation by means of a boundary model we recently developed, which enable to trace the sub-Alfvenic MHD responses of the corona numerically. The simulated coronal features include the formation of the two twisted coronal magnetic field structures along the magnetically inversion lines at the lowermost corona (coinciding the two observed filaments at west-north part of the solar disk) and the large-scale outward motions and decay of the closed-field streamer above the two twisted-field regions. Our MHD simulation model did not include the triggering event directly, and our simulations were done in somewhat low resolution in space. However, the reasonable success in reproducing coronal features relating a specific event in a well-known manner (using the synoptic map format data and the MHD simulation model) shows that the new dataset from HMI will be useful for the models, such as the MHD and the potential field models, as the previous dataset by SOHO/MDI.

  16. EMAPS: An Efficient Multiscale Approach to Plasma Systems with Non-MHD Scale Effects

    SciTech Connect

    Omelchenko, Yuri A.

    2016-08-08

    we have developed a novel Event-driven Multiscale Asynchronous Parallel Simulation (EMAPS) technology that replaces time stepping with self-adaptive update events. Local calculations are carried out only on an “as needed basis”. EMAPS (i) guarantees accurate and stable processing of physical variables in time accurate simulations, and (ii) eliminates unnecessary computation. Applying EMAPS to the hybrid model has resulted in the development of a unique parallel code, dimension-independent (compile-time-configurable) HYPERS (Hybrid Parallel Event-Resolved Simulator) that scales to hundreds of thousands of parallel processors. HYPERS advances electromagnetic fields and particles asynchronously on time scales determined by local physical laws and mesh properties. To achieve high computational accuracy in complex device geometries, HYPERS employs high-fidelity Cartesian grids with masked conductive cells. The HYPERS model includes multiple ion species, energy and momentum conserving ion-ion collisions, and provides a number of approximations for plasma resistivity and vacuum regions. Both local and periodic boundary conditions are allowed. The HYPERS solver preserves zero divergence of magnetic field. The project has demonstrated HYPERS capabilities on a number of applications of interest to fusion and astrophysical plasma physics applications listed below. 1. Theta-pinch formation of FRCs The formation, spontaneous spin-up, and stability of theta-pinch formed field-reversed configurations have been studied self-consistently in 3D. The end-to-end hybrid simulations reveal poloidal profiles of implosion-driven fast toroidal plasma rotation and demonstrate three discharge regimes as a function of experimental parameters: the decaying stable configuration, the tilt unstable configuration, and the nonlinear evolution of a fast growing tearing mode. 2. FRC collisions with magnetic mirrors Interactions of fast plasma streams and objects with magnetic obstacles (dipoles

  17. Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere.

    PubMed

    Claudepierre, S G; Toffoletto, F R; Wiltberger, M

    2016-01-01

    We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.

  18. Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere

    NASA Astrophysics Data System (ADS)

    Claudepierre, S. G.; Toffoletto, F. R.; Wiltberger, M.

    2016-01-01

    We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.

  19. Theoretical and Experimental Research of Capabilities of MHD Technology to Control Gas Flow with Non-Equilibrium Ionization

    DTIC Science & Technology

    2007-11-02

    experimental research of capabilities of using of MHD technology to control gas flow with non-equilibrium ionization. Cold gas flows will be considered, where...and MHD generator will be developed. Requirements to ionizer, MHD generator and flow parameters at which self- sustained operational mode of ionizer and...MHD generator is realized will be formulated. Possibilities of using of MHD control in gas-dynamical systems will be considered. Traditional use of

  20. Adaptive mesh refinement for singular structures in incompressible MHD and compressible Hall-MHD with electron and ion inertia

    NASA Astrophysics Data System (ADS)

    Grauer, R.; Germaschewski, K.

    The goal of this presentation is threefold. First, the role of singular structures like shocks, vortex tubes and current sheets for understanding intermittency in small scale turbulence is demonstrated. Secondly, in order to investigate the time evolution of singular structures, effective numerical techniques have to be applied, like block structured adaptive mesh refinement combined with recent advances in treating hyperbolic equations. And thirdly, the developed numerical techniques can perfectly be applied to the question of fast reconnection demonstrated by the example of compressible Hall-MHD including electron and ion inertia. 1 Why is it worth studying singular structures? The motivation for studying singular structures has several sources. In turbulent fluid and plasma flows the formation of nearly singular structures like shocks, vortex tubes or current sheets provide an effective mechanism to transport energy from large to small scales. In the last years it has become clear that the nature of the singular structures is a key feature of small scale intermittency. In a phenomenological way this is established in She-Leveque like models (She and Leveque, 1994; Grauer, Krug and Marliani, 1994; Politano and Pouquet, 1995; M¨uller and Biskamp, 2000), which are able to describe some of the scaling properties of high order structure functions. An additional source which highlights the importance of singular structures originates from studies of a toy model of turbulence, the so-called Burgers turbulence. The very left tail of the probability distribution of velocity increments can be calculated using the instanton approach (Balkovsky, Falkovich, Kolokolov and Lebedev, 1997). Here it is interesting to note that the main contribution in the relevant path integral stems from the the singular structures which are shocks in the burgers turbulence. From a mathematical point of view the question whether

  1. EFFECTS OF RESISTIVITY ON MAGNETIZED CORE-COLLAPSE SUPERNOVAE

    SciTech Connect

    Sawai, H.; Suzuki, H.; Yamada, S.; Kotake, K.

    2013-02-10

    We studied the role of turbulent resistivity in the core-collapse of a strongly magnetized massive star, carrying out two-dimensional resistive-MHD simulations. Three cases with different initial strengths of magnetic field and rotation are investigated: (1) a strongly magnetized rotating core, (2) a moderately magnetized rotating core, and (3) a very strongly magnetized non-rotating core. In each case, one ideal-MHD model and two resistive-MHD models are computed. As a result of these computations, each model shows an eruption of matter assisted by magnetic acceleration (and also by centrifugal acceleration in the rotating cases). We found that resistivity attenuates the explosion in cases 1 and 2, while it enhances the explosion in case 3. We also found that in the rotating cases, the main mechanisms for the amplification of a magnetic field in the post-bounce phase are an outward advection of the magnetic field and a twisting of poloidal magnetic field lines by differential rotation, which are somewhat dampened down with the presence of resistivity. Although magnetorotational instability seems to occur in the rotating models, it plays only a minor role in magnetic field amplification. Another impact of resistivity is that on the aspect ratio. In the rotating cases, a large aspect ratio of the ejected matter, >2.5, attained in an ideal-MHD model is reduced to some extent in a resistive model. These results indicate that resistivity possibly plays an important role in the dynamics of strongly magnetized supernovae.

  2. Multi-MW Closed Cycle MHD Nuclear Space Power Via Nonequilibrium He/Xe Working Plasma

    NASA Technical Reports Server (NTRS)

    Litchford, Ron J.; Harada, Nobuhiro

    2011-01-01

    Prospects for a low specific mass multi-megawatt nuclear space power plant were examined assuming closed cycle coupling of a high-temperature fission reactor with magnetohydrodynamic (MHD) energy conversion and utilization of a nonequilibrium helium/xenon frozen inert plasma (FIP). Critical evaluation of performance attributes and specific mass characteristics was based on a comprehensive systems analysis assuming a reactor operating temperature of 1800 K for a range of subsystem mass properties. Total plant efficiency was expected to be 55.2% including plasma pre-ionization power, and the effects of compressor stage number, regenerator efficiency and radiation cooler temperature on plant efficiency were assessed. Optimal specific mass characteristics were found to be dependent on overall power plant scale with 3 kg/kWe being potentially achievable at a net electrical power output of 1-MWe. This figure drops to less than 2 kg/kWe when power output exceeds 3 MWe. Key technical issues include identification of effective methods for non-equilibrium pre-ionization and achievement of frozen inert plasma conditions within the MHD generator channel. A three-phase research and development strategy is proposed encompassing Phase-I Proof of Principle Experiments, a Phase-II Subscale Power Generation Experiment, and a Phase-III Closed-Loop Prototypical Laboratory Demonstration Test.

  3. A parallel code base on discontinuous Galerkin method on three dimensional unstructured meshes for MHD equations

    NASA Astrophysics Data System (ADS)

    Li, Xujing; Zheng, Weiying

    2016-10-01

    A new parallel code based on discontinuous Galerkin (DG) method for hyperbolic conservation laws on three dimensional unstructured meshes is developed recently. This code can be used for simulations of MHD equations, which are very important in magnetic confined plasma research. The main challenges in MHD simulations in fusion include the complex geometry of the configurations, such as plasma in tokamaks, the possibly discontinuous solutions and large scale computing. Our new developed code is based on three dimensional unstructured meshes, i.e. tetrahedron. This makes the code flexible to arbitrary geometries. Second order polynomials are used on each element and HWENO type limiter are applied. The accuracy tests show that our scheme reaches the desired three order accuracy and the nonlinear shock test demonstrate that our code can capture the sharp shock transitions. Moreover, One of the advantages of DG compared with the classical finite element methods is that the matrices solved are localized on each element, making it easy for parallelization. Several simulations including the kink instabilities in toroidal geometry will be present here. Chinese National Magnetic Confinement Fusion Science Program 2015GB110003.

  4. Linear stability of ideal MHD configurations. II. Results for stationary equilibrium configurations

    NASA Astrophysics Data System (ADS)

    Demaerel, T.; Keppens, R.

    2016-12-01

    In this paper, we continue exploring the consequences of the general equation of motion (EOM) governing all Lagrangian perturbations ξ about a time-dependent, ideal magnetohydrodynamic (MHD) configuration, which includes self-gravity, external gravity, pressure gradients, compressibility, inertial effects, and anisotropic Lorentz force. We here address the specific case of MHD stability for 3D stationary equilibria, where the perturbed EOM features a symmetric operator F and an antisymmetric Doppler-Coriolis operator v . ∇ . For this case, we state and prove the general properties for the solutions ξ of the governing dynamical system. For axisymmetric perturbations about axisymmetric equilibria with purely toroidal, or purely poloidal magnetic fields, specific stability theorems can be formulated. We derive a useful integral expression for the quadratic quantity given by the inner product ⟨ ξ , F [ ξ ] ⟩ . For deriving stability statements on MHD states where self-gravity is involved as well, we provide an upper bound on the perturbed self-gravitational energy associated with the displacement ξ . The resulting expression elucidates the role of potentially stabilizing versus destabilizing contributions and shows the role of gravity, entropy gradients, velocity shear, currents, Lorentz forces, inertia, and pressure gradients in offering many routes to unstable behavior in flowing gases and plasmas. These have historically mostly been studied for static v = 0 configurations, looking at stability of exactly force-balanced states, or by assuming stationarity similar to our approach here (i.e., ∂ t ≡ 0 for the state we perturb), but typically in combination with some reduced dimensionality on the configuration of interest (translational or axisymmetry). We show that in these limits, we find and generalize expressions well-known from, e.g., the study of ideal MHD stability of tokamak plasmas or from Schwarzschild's criteria controlling convection in

  5. Efficacy of a new pharmacokinetically enhanced formulation of amoxicillin/clavulanate (2000/125 mg) in adults with community-acquired pneumonia caused by Streptococcus pneumoniae, including penicillin-resistant strains.

    PubMed

    File, Thomas M; Garau, Javier; Jacobs, Michael R; Wynne, Brian; Twynholm, Monique; Berkowitz, Elchonon

    2005-02-01

    Community-acquired pneumonia (CAP) is a common respiratory illness, frequently caused by Streptococcus pneumoniae. The prevalence of S. pneumoniae resistance to common antimicrobials has increased over recent years. A new pharmacokinetically enhanced formulation of amoxicillin/clavulanate (2000/125 mg) has been developed, designed to combat infections caused by S. pneumoniae, including penicillin-resistant (PRSP, penicillin minimum inhibitory concentrations (MICs) >or=2mg/l) isolates, and those with elevated amoxicillin/clavulanic acid MICs, while maintaining coverage of beta-lactamase-producing pathogens. A pooled efficacy analysis of four randomized (1:1) and one non-comparative clinical trials of amoxicillin/clavulanate, 2000/125 mg, given twice daily, was conducted in adult patients with CAP. Comparator agents were conventional amoxicillin/clavulanate formulations. At follow-up (days 16-39), efficacy (eradication of the initial pathogen or clinical cure in patients for whom no repeat culture was performed) in patients with S. pneumoniae infection was 92.3% (274/297) for amoxicillin/clavulanate, 2000/125 mg and 85.2% (46/54) for comparators (P=0.11). Twenty-four of 25 PRSP-infected patients receiving amoxicillin/clavulanate, 2000/125 mg were treated successfully. Both amoxicillin/clavulanate, 2000/125 mg and comparators were well tolerated, with few patients withdrawing from the studies.

  6. A highly acid-resistant novel strain of Lactobacillus johnsonii No. 1088 has antibacterial activity, including that against Helicobacter pylori, and inhibits gastrin-mediated acid production in mice

    PubMed Central

    Aiba, Yuji; Nakano, Yasuhiro; Koga, Yasuhiro; Takahashi, Kenji; Komatsu, Yasuhiko

    2015-01-01

    A novel strain of Lactobacillus johnsonii No. 1088 was isolated from the gastric juice of a healthy Japanese male volunteer, and characterized for its effectiveness in the stomach environment. Lactobacillus johnsonii No. 1088 was found to have the strongest acid resistance among several lactobacilli examined (>10% of cells survived at pH 1.0 after 2 h), and such a high acid resistance property was a specific characteristic of this strain of L. johnsonii. When cultured with various virulent bacteria, L. johnsonii No. 1088 inhibited the growth of Helicobacter pylori,Escherichia coli O-157, Salmonella Typhimurium, and Clostridium difficile, in which case its effectiveness was more potent than that of a type strain of L. johnsonii,JCM2012. In addition to its effect in vitro, L. johnsonii No. 1088 inhibited the growth of H. pylori in human intestinal microbiota-associated mice in both its live and lyophilized forms. Moreover, L. johnsonii No. 1088 suppressed gastric acid secretion in mice via decreasing the number of gastrin-positive cells in the stomach. These results taken together suggest that L. johnsonii No. 1088 is a unique lactobacillus having properties beneficial for supporting H. pylori eradication by triple therapy including the use of a proton pump inhibitor (PPI) and also for prophylaxis of gastroesophageal reflux disease possibly caused after H. pylori eradication as a side effect of PPI. PMID:25771812

  7. US/USSR cooperative program in open-cycle MHD electrical power generation: joint test report No. 4. Tests in the U-25B facility: MHD generator tests No. 6 and 7

    SciTech Connect

    Picologlou, B F; Batenin, V M

    1981-01-01

    A description of the main results obtained during Tests No. 6 and 7 at the U-25B Facility using the new channel No. 2 is presented. The purpose of these tests was to operate the MHD generator at its design parameters. Described here are new plasma diagnostic devices: a traversing dual electrical probe for determining distribution of electron concentrations, and a traversing probe that includes a pitot tube for measuring total and static pressure, and a light detector for measuring plasma luminescence. Data are presented on heat flux distribution along the channel, the first data of this type obtained for an MHD facility of such size. Results are given of experimental studies of plasma characteristics, gasdynamic, thermal, and electrical MHD channel performance, and temporal and spatial nonuniformities. Typical modes of operation are analyzed by means of local electrical analyses. Computer models are used to obtain predictions for both localized and overall generator characteristics. These theoretical predictions agree closely with the results of the local analyses, as well as with measurements of the overall gasdynamic and electrical characteristics of the generator.

  8. Vorticity equation for MHD fast waves in geospace environment

    NASA Technical Reports Server (NTRS)

    Yamauchi, M.; Lundin, R.; Lui, A. T. Y.

    1993-01-01

    The MHD vorticity equation is modified in order to apply it to nonlinear MHD fast waves or shocks when their extent along the magnetic field is limited. Field-aligned current (FAC) generation is also discussed on the basis of this modified vorticity equation. When the wave normal is not aligned to the finite velocity convection and the source region is spatially limited, a longitudinal polarization causes a pair of plus and minus charges inside the compressional plane waves or shocks, generating a pair of FACs. This polarization is not related to the separation between the electrons and ions caused by their difference in mass, a separation which is inherent to compressional waves. The resultant double field-aligned current structure exists both with and without the contributions from curvature drift, which is questionable in terms of its contribution to vorticity change from the viewpoint of single-particle motion.

  9. Current distribution and nonuniformity effects in MHD disk generators

    NASA Astrophysics Data System (ADS)

    Roseman, D. F.

    1982-08-01

    Current distribution and nonuniformity effects in combustion driven MHD disk generators were studied. The importance of these phenomena to baseload power generation was investigated. The peg wall construction allowed current and voltage distributions to be measured. The channel was operated with plasma temperatures up to 2750 K and magnetic field strengths up to 5.5 Tesla. The magnitudes of the currents and voltages were reduced by significant loss mechanisms, primarily electrode losses and current leakage through the wall caused by potassium seed penetration of the castable ceramic between the pegs. A simple circuit model accounting for these losses was developed to be compared with analytical calculations. Under normal uniform electrical loading the distributions measured in the channel were uniform as expected. Nonuniform electrical loading was used to produce and measure effects on the current distribution that occur only in the presence of high magnetic fields as required for MHD power generation.

  10. High-magnetic-field MHD-generator program

    NASA Astrophysics Data System (ADS)

    Kruger, C. H.; Eustis, R. H.; Mitchner, M.; Self, S. A.; Koester, J. K.; Nakamura, T.

    1981-04-01

    Channel phenomena which are important at high magnetic fields are investigated. Nonuniformity effects, boundary layers, hall field breakdown, the effects of electrode configuration and current concentrations, and studies of steady state combustion disk and linear channels in a 6 Tesla magnet of small dimensions were studied. A multi-channel fiber optics diagnostic system is described. A one dimensional model to describe the performance of a non-ideal MHD generator was developed. A two dimensional MHD computer code was developed which predicts the dependence on electrode and insulator dimensions of the onset of interelectrode Hall field breakdown. Calculations of the effects of nonuniformities on the flow and electrical behavior of baseload-sized disk generators were performed.

  11. Efficiently Finding Trends in Macroscopic MHD Stability Using Perturbed Equilibria

    NASA Astrophysics Data System (ADS)

    Comer, K. J.; Callen, J. D.; Hegna, C. C.; Turnbull, A. D.; Cowley, S. C.

    2001-10-01

    The effects of equilibrium shaping and profiles on long wavelength ideal MHD instabilities in toroidal plasmas are traditionally studied using numerical parameter scans. Previously, we introduced a new perturbative technique to explore these dependencies: assuming small equilibrium variations, new stability properties are found using a perturbation of the energy principle rather than with a traditional stability code. With this approach, stability dependencies can be efficiently examined without numerically generating complete MHD stability results for every set of parameters (which can be time-intensive for accurate representations of several configurations). Here, we briefly expand on previous successful perturbed stability analyses for screw pinch equilibria by discussing cases where the approach fails. Next, we extend the approach to toroidal geometry using the GATO and TOQ codes, and present cases that both validate the approach and suggest caution in its application.

  12. MHD-waves in the geomagnetic tail: A review

    NASA Astrophysics Data System (ADS)

    Leonovich, Anatoliy; Mazur, Vitaliy; Kozlov, Daniil

    2015-03-01

    This article presents the review of experimental and theoretical studies on ultra-lowfrequency MHD oscillations of the geomagnetic tail. We consider the Kelvin-Helmholtz instability at the magnetopause, oscillations with a discrete spectrum in the "magic frequencies"range, the ballooning instability of coupled Alfvén and slow magnetosonic waves, and "flapping" oscillations of the current sheet of the geomagnetic tail. Over the last decade, observations from THEMIS, CLUSTER and Double Star satellites have been of great importance for experimental studies. The use of several spacecraft allows us to study the structure of MHD oscillations with high spatial resolution. Due to this, we can make a detailed comparison between theoretical results and those obtained from multi-spacecraft studies. To make such comparisons in theoretical studies, in turn, we have to use the numerical models closest to the real magnetosphere.

  13. Performance calculations for 1000 MWe MHD/steam power plants

    NASA Technical Reports Server (NTRS)

    Pian, C. C. P.

    1981-01-01

    The effects of MHD generator operating conditions and constraints on the performance of MHD/steam power plants are investigated. Power plants using high temperature combustion air preheat (2500 F) and plants using intermediate temperature preheat (1100 F) with oxygen enrichment are considered. Variations of these two types of power plants are compared on the basis of fixed total electrical output (1000 MWe). Results are presented to show the effects of generator plant length and level of oxygen enrichment on the plant thermodynamic efficiency and on the required generator mass flow rate. Factors affecting the optimum levels of oxygen enrichment are analyzed. It is shown that oxygen enrichment can reduce magnet stored energy requirement.

  14. Integrated Modeling of Time Evolving 3D Kinetic MHD Equilibria and NTV Torque

    NASA Astrophysics Data System (ADS)

    Logan, N. C.; Park, J.-K.; Grierson, B. A.; Haskey, S. R.; Nazikian, R.; Cui, L.; Smith, S. P.; Meneghini, O.

    2016-10-01

    New analysis tools and integrated modeling of plasma dynamics developed in the OMFIT framework are used to study kinetic MHD equilibria evolution on the transport time scale. The experimentally observed profile dynamics following the application of 3D error fields are described using a new OMFITprofiles workflow that directly addresses the need for rapid and comprehensive analysis of dynamic equilibria for next-step theory validation. The workflow treats all diagnostic data as fundamentally time dependent, provides physics-based manipulations such as ELM phase data selection, and is consistent across multiple machines - including DIII-D and NSTX-U. The seamless integration of tokamak data and simulation is demonstrated by using the self-consistent kinetic EFIT equilibria and profiles as input into 2D particle, momentum and energy transport calculations using TRANSP as well as 3D kinetic MHD equilibrium stability and neoclassical transport modeling using General Perturbed Equilibrium Code (GPEC). The result is a smooth kinetic stability and NTV torque evolution over transport time scales. Work supported by DE-AC02-09CH11466.

  15. Comparing nonlinear MHD simulations of low-aspect-ratio RFPs to RELAX experiments

    NASA Astrophysics Data System (ADS)

    McCollam, K. J.; den Hartog, D. J.; Jacobson, C. M.; Sovinec, C. R.; Masamune, S.; Sanpei, A.

    2016-10-01

    Standard reversed-field pinch (RFP) plasmas provide a nonlinear dynamical system as a validation domain for numerical MHD simulation codes, with applications in general toroidal confinement scenarios including tokamaks. Using the NIMROD code, we simulate the nonlinear evolution of RFP plasmas similar to those in the RELAX experiment. The experiment's modest Lundquist numbers S (as low as a few times 104) make closely matching MHD simulations tractable given present computing resources. Its low aspect ratio ( 2) motivates a comparison study using cylindrical and toroidal geometries in NIMROD. We present initial results from nonlinear single-fluid runs at S =104 for both geometries and a range of equilibrium parameters, which preliminarily show that the magnetic fluctuations are roughly similar between the two geometries and between simulation and experiment, though there appear to be some qualitative differences in their temporal evolution. Runs at higher S are planned. This work is supported by the U.S. DOE and by the Japan Society for the Promotion of Science.

  16. Comet 1P/Halley Multifluid MHD Model for the Giotto Fly-by

    NASA Astrophysics Data System (ADS)

    Rubin, M.; Combi, M. R.; Daldorff, L. K. S.; Gombosi, T. I.; Hansen, K. C.; Shou, Y.; Tenishev, V. M.; Tóth, G.; van der Holst, B.; Altwegg, K.

    2014-02-01

    The interaction of comets with the solar wind has been the focus of many studies including numerical modeling. We compare the results of our multifluid MHD simulation of comet 1P/Halley to data obtained during the flyby of the European Space Agency's Giotto spacecraft in 1986. The model solves the full set of MHD equations for the individual fluids representing the solar wind protons, the cometary light and heavy ions, and the electrons. The mass loading, charge-exchange, dissociative ion-electron recombination, and collisional interactions between the fluids are taken into account. The computational domain spans over several million kilometers, and the close vicinity of the comet is resolved to the details of the magnetic cavity. The model is validated by comparison to the corresponding Giotto observations obtained by the Ion Mass Spectrometer, the Neutral Mass Spectrometer, the Giotto magnetometer experiment, and the Johnstone Plasma Analyzer instrument. The model shows the formation of the bow shock, the ion pile-up, and the diamagnetic cavity and is able to reproduce the observed temperature differences between the pick-up ion populations and the solar wind protons. We give an overview of the global interaction of the comet with the solar wind and then show the effects of the Lorentz force interaction between the different plasma populations.

  17. Comet 1P/Halley multifluid MHD model for the Giotto fly-by

    SciTech Connect

    Rubin, M.; Altwegg, K.; Combi, M. R.; Daldorff, L. K. S.; Gombosi, T. I.; Hansen, K. C.; Shou, Y.; Tenishev, V. M.; Tóth, G.; Van der Holst, B.

    2014-02-01

    The interaction of comets with the solar wind has been the focus of many studies including numerical modeling. We compare the results of our multifluid MHD simulation of comet 1P/Halley to data obtained during the flyby of the European Space Agency's Giotto spacecraft in 1986. The model solves the full set of MHD equations for the individual fluids representing the solar wind protons, the cometary light and heavy ions, and the electrons. The mass loading, charge-exchange, dissociative ion-electron recombination, and collisional interactions between the fluids are taken into account. The computational domain spans over several million kilometers, and the close vicinity of the comet is resolved to the details of the magnetic cavity. The model is validated by comparison to the corresponding Giotto observations obtained by the Ion Mass Spectrometer, the Neutral Mass Spectrometer, the Giotto magnetometer experiment, and the Johnstone Plasma Analyzer instrument. The model shows the formation of the bow shock, the ion pile-up, and the diamagnetic cavity and is able to reproduce the observed temperature differences between the pick-up ion populations and the solar wind protons. We give an overview of the global interaction of the comet with the solar wind and then show the effects of the Lorentz force interaction between the different plasma populations.

  18. Method of rapid determination of MHD equilibrium properties with the modified version of the SURFAS code

    SciTech Connect

    Lee, D.K.; Hirshman, S.P.; Okabayashi, M.; Reusch, M.F.; Sun, Y.C.

    1993-09-01

    Rapid determination of MHD eqilibrium properties of tokamak plasmas is carried out by means of an approximation method based on the use of database files. These are computed a priori from MHD equilibrium solutions obtained by performing reconstruction to match experimental measurements, which include motional Stark effect (MSE) data. The procedure carries out a single iteration of Newton`s method to determine the poloidal variation of the toroidal plasma current density in the equilibrium form j{sub {phi}} = {minus}2{pi}({mu}{sub 0}Rp{prime} + FF{prime}/R) by representing p{prime}({psi}) and F({psi})F{prime}({psi}) in series expansions of Chebyshev polynomials. The polynominal expansion coefficients are obtained through a least-squares data fitting process similar to that used in the equilibrium reconstruction. Knowing the current density j{phi} allows the determination of the internal q-profile from the MSE data. This important stability parameter is generally unavailable from a current filament model. Numerical results calculated in this approach are compared with those determined from an accurate solution of the Grad-Shafranov equation, subject to a similar set of magnetic and pressure measurement constraints.

  19. Gigawatt, Closed Cycle, Vapor Core-Mhd Space Power System Conceptual Design Study

    NASA Astrophysics Data System (ADS)

    Wetch, Joseph R.; Rhee, Hyop S.; Koester, J. Kent; Goodman, Julius; Maya, Issac

    1988-04-01

    A conceptual design study for a closed cycle gigawatt electric space power system has been conducted. The closed cycle static operation reduces power system interaction effects upon the space craft. This system utilizes a very high temperature (5500 K) plasma core reactor and a magnetohydrodynamic (MHD) power conversion subsystem to provide a power density of about 8 kWe/kg (0.13 kg/kWe) for several kilo-seconds. Uranium vapor is the fuel. Candidate working fluids are metal vapors such as lithium or calcium. The system is based on a Rankine cycle to minimize the electromagnetic pumping power requirement. The fission fragment induced nonequilibrium ionization in the plasma in the MHD power duct provides the plasma electric conductivity for gigawatt power generation. Waste heat is rejected utilizing lithium heat pipes at temperatures just below 2000 K, thus minimizing the radiator area requirement. Key technology issues are identified, including the containment of the 5500 K 'sun-liken plasma at 4 to 0 MPa In a reflector moderated, gas/vapor filled cavity core reactor. A promising scheme to protect the refractory metal reactor inner wall is presented, together with a heating load analysis in the wall. This scheme utilizes an ablating film of liquid lithium/calcium that evaporates into the cavity core to become the working fluid of the cycle.

  20. Global Extended MHD Studies of Fast Magnetic Reconnection

    SciTech Connect

    Breslau J.A.; Jardin, S.C.

    2002-09-18

    Recent experimental and theoretical results have led to two lines of thought regarding the physical processes underlying fast magnetic reconnection. One is based on the traditional Sweet-Parker model but replaces the Spitzer resistivity with an enhanced resistivity caused by electron scattering by ion acoustic turbulence. The other includes the finite gyroradius effects that enter Ohm's law through the Hall and electron pressure gradient terms. A 2-D numerical study, conducted with a new implicit parallel two-fluid code, has helped to clarify the similarities and differences in predictions between these two models and provides some insight into their respective ranges of validity.