bluuebunny/crossref_metadata_2025 huggingface dataset:
A new viscous instability in weakly ionised protoplanetary discs
Authors: Johansen Anders , Kato Mariko , Sano Takayoshi
Published: June 2011

Large regions of protoplanetary discs are believed to be too weakly ionised to support magnetorotational instabilities, because abundant tiny dust grains soak up free electrons and reduce the conductivity of the gas. At the outer edge of this “dead zone”, the ionisation fraction increases gradually and the resistivity drops until the magnetorotational instability can develop turbulence. We identify a new viscous instability which operates in the semi-turbulent transition region between “dead” and “alive” zones. The strength of the saturated turbulence depends strongly on the local resistivity in this transition region. A slight increase (decrease) in dust density leads to a slight increase (decrease) in resistivity and a slight decrease (increase) in turbulent viscosity. Such spatial variation in the turbulence strength causes a mass pile-up where the turbulence is weak, leading to a run-away process where turbulence is weakened and mass continues to pile up. The final result is the appearance of high-amplitude pressure bumps and deep pressure valleys. Here we present a local linear stability analysis of weakly ionised accretion discs and identify the linear instability responsible for the pressure bumps. A paper in preparation concerns numerical results which confirm and expand the existence of the linear instability.
Weakly imbalanced strong turbulence
Authors: Beresnyak Andrey
Published: June 2011

The theory of strong MHD turbulence with cross-helicity has been a subject of many recent studies. In this paper we focused our attention on low-imbalance limit and performed high-resolution 3D simulations. The results suggest that in this limit both w+=v+b and w−=v−b are cascaded strongly. The model for imbalance based on so-called “dynamic alignment” strongly contradicts numerical evidence.
Similarity of Jupiter and RRATs
Authors: Gezer Ilknur , Pekünlü E. Rennan
Published: June 2011

In the present investigation, radial diffusion of equatorially trapped electrons in the magnetospheres of Jupiter and Rotating Radio Transients (RRATs) are examined and compared. It is assumed that electrons lose energy through synchrotron radiation and the wave-particle interaction. The phase space density of the electrons, which go through gradB drift in Jupiter's and RRATs magnetospheres and thus resonate with the plasma waves, changes and this change predicted by the model seems to be consistent with the Pioneer 10 and Pioneer 11 data for Jupiter's case and a similar result obtained for RRATs.
On the development of a spherical hybrid model - Lessons and applications
Authors: Dyadechkin S. , Kallio E. , Jarvinen R. , Janhunen P. , Semenov V. S. , Biernat H. K.
Published: June 2011

We are developing a spherical hybrid model to study how the solar wind interacts with the solar system bodies. In this brief status report we introduce some lessons from the spherical grid development and illustrate the usage of the new model by showing a preliminary test run.
Development of the PFO–CFO hypothesis of solar system formation: Why do the celestial objects have different isotopic ratios for some chemical elements?
Authors: Kadyshevich E. A. , Ostrovskii V. E.
Published: June 2011

The Solar System formation PFO–CFO hypothesis is developed in the direction of creation of a phenomenological model focused on solution of a number of paradoxes and answering to a number of mysterious questions under the same cover. For explanation of the events and processes that occurred over the period from the middle ages of the pre-solar star to the Solar System formation, original approaches are applied.
A note on using thermally driven solar wind models in MHD space weather simulations
Authors: Pomoell Jens , Vainio Rami
Published: June 2011

One of the challenges in constructing global magnetohydrodynamic (MHD) models of the inner heliosphere for, e.g., space weather forecasting purposes, is to correctly capture the acceleration and expansion of the solar wind. In many current models, the solar wind is driven by varying the polytropic index so that a desired heating is obtained. While such schemes can yield solar wind properties consistent with observations, they are not problem-free. In this work, we demonstrate by performing MHD simulations that altering the polytropic index affects the properties of propagating shocks significantly, which in turn affect the predicted space weather conditions. Thus, driving the solar wind with such a mechanism should be used with care in simulations where correctly capturing the shock physics is essential. As a remedy, we present a simple heating function formulation by which the polytropic wind can be used while still modeling the shock physics correctly.
On radiation-zone dynamos
Authors: Rüdiger Günther , Gellert Marcus , Arlt Rainer
Published: June 2011

It is shown that the magnetic current-driven (‘kink-type’) instability produces flow and field patterns with helicity and even with α-effect but only if the magnetic background field possesses non-vanishing current helicity B⋅ curl B by itself. Fields with positive large-scale current helicity lead to negative small-scale kinetic helicity. The resulting α-effect is positive. These results are very strict for cylindric setups without z-dependence of the background fields. The sign rules also hold for the more complicated cases in spheres where the toroidal fields are the result of the action of differential rotation (induced from fossil poloidal fields) at least for the case that the global rotation is switched off after the onset of the instability.
Emergence of intermittent structures and reconnection in MHD turbulence
Authors: Greco Antonella , Servidio Sergio , Matthaeus William H. , Dmitruk Pablo
Published: June 2011

In recent analyses of numerical simulation and solar wind dataset, the idea that the magnetic discontinuities may be related to intermittent structures that appear spontaneously in MHD turbulence has been explored in details. These studies are consistent with the hypothesis that discontinuity events founds in the solar wind might be of local origin as well, i.e. a by-product of the turbulent evolution of magnetic fluctuations.

Using simulations of 2D MHD turbulence, we are exploring a possible link between tangential discontinuities and magnetic reconnection. The goal is to develop numerical algorithms that may be useful for solar wind applications.
Coupled Alfvén and kink oscillations in an inhomogeneous corona
Authors: Pascoe David J. , Wright Andrew N. , De Moortel Ineke
Published: June 2011

We perform 3D numerical simulations of footpoint-driven transverse waves propagating in a low β plasma. The presence of inhomogeneities in the density profile leads to the coupling of the driven kink mode to Alfvén modes by resonant absorption. The decay of the propagating kink wave as energy is transferred to the local Alfvén mode is in good agreement with a modified interpretation of the analytical expression derived for standing kink modes. This coupling may account for the damping of transverse velocity perturbation waves which have recently been observed to be ubiquitous in the solar corona.
Weak turbulence theory of dispersive waves in the solar corona
Authors: Spanier Felix , Vainio Rami
Published: June 2011

The interaction of plasma waves plays a crucial role in the dynamics of weakly turbulent plasmas. So far the interaction of non-dispersive waves has been studied. In this paper the theory is extended to dispersive waves. It is well known that dispersive waves may be found in the solar corona, where they contribute to the heating of the corona. Here the possible interactions in the solar corona are described and the interaction rates are derived in the framework of Hall MHD.
The effect of plume/interplume lanes on ion-cyclotron resonance heating
Authors: Doğan Suzan , Pekünlü E. Rennan
Published: June 2011

The effect of the Plume/Interplume Lane (PIPL) structure of the solar North Polar Coronal Hole (NPCH) on the ion-cyclotron resonance (ICR) process is investigated. The ICR process in the interplume lanes is much more effective than in the plumes, agreeing with the observations which show the source of fast solar wind is interplume lanes.
Small-scale flux emergence events observed by Sunrise/IMaX
Authors: Guglielmino S. L. , Pillet V. Martínez , del Toro Iniesta J. C. , Rubio L. R. Bellot , Zuccarello F. , Solanki S. K. ,   the Sunrise/IMaX team
Published: June 2011

Thanks to the unprecedented combination of high spatial resolution (0″.2) and high temporal cadence (33 s) spectropolarimetric measurements, the IMaX magnetograph aboard the Sunrise balloon-borne telescope is revealing new insights about the plasma dynamics of the all-pervasive small-scale flux concentrations in the quiet Sun. We present the result of a case study concerning the appearance of a bipole, with a size of about 4″ and a flux content of 5 × 1017 Mx, with strong signal of horizontal fields during the emergence. We analyze the data set using the SIR inversion code and obtain indications about the three-dimensional shape of the bipole and its evolution with time.
An hybrid neuro-wavelet approach for long-term prediction of solar wind
Authors: Napoli Christian , Bonanno Francesco , Capizzi Giacomo
Published: June 2011

Nowadays the interest for space weather and solar wind forecasting is increasing to become a main relevance problem especially for telecommunication industry, military, and for scientific research. At present the goal for weather forecasting reach the ultimate high ground of the cosmos where the environment can affect the technological instrumentation. Some interests then rise about the correct prediction of space events, like ionized turbulence in the ionosphere or impacts from the energetic particles in the Van Allen belts, then of the intensity and features of the solar wind and magnetospheric response. The problem of data prediction can be faced using hybrid computation methods so as wavelet decomposition and recurrent neural networks (RNNs). Wavelet analysis was used in order to reduce the data redundancies so obtaining representation which can express their intrinsic structure. The main advantage of the wavelet use is the ability to pack the energy of a signal, and in turn the relevant carried informations, in few significant uncoupled coefficients. Neural networks (NNs) are a promising technique to exploit the complexity of non-linear data correlation. To obtain a correct prediction of solar wind an RNN was designed starting on the data series. As reported in literature, because of the temporal memory of the data an Adaptative Amplitude Real Time Recurrent Learning algorithm was used for a full connected RNN with temporal delays. The inputs for the RNN were given by the set of coefficients coming from the biorthogonal wavelet decomposition of the solar wind velocity time series. The experimental data were collected during the NASA mission WIND. It is a spin stabilized spacecraft launched in 1994 in a halo orbit around the L1 point. The data are provided by the SWE, a subsystem of the main craft designed to measure the flux of thermal protons and positive ions.
A shell model for turbulent dynamos
Authors: Nigro G. , Perrone D. , Veltri P.
Published: June 2011

A self-consistent nonlinear dynamo model is presented. The nonlinear behavior of the plasma at small scale is described by using a MHD shell model for fields fluctuations; this allow us to study the dynamo problem in a large parameter regime which characterizes the dynamo phenomenon in many natural systems and which is beyond the power of supercomputers at today. The model is able to reproduce dynamical situations in which the system can undergo transactions to different dynamo regimes. In one of these the large-scale magnetic field jumps between two states reproducing the magnetic polarity reversals. From the analysis of long time series of reversals we infer results about the statistics of persistence times, revealing the presence of hidden long-time correlations in the chaotic dynamo process.
Energetic particle acceleration and transport by Alfvén/acoustic waves in tokamak-like Solar flares
Authors: Obergaulinger Martin , García-Muñoz Manuel
Published: June 2011

Alfven/acoustic waves are ubiquitous in astrophysical as well as in laboratory plasmas. Their interplay with energetic ions is of crucial importance to understanding the energy and particle exchange in astrophysical plasmas as well as to obtaining a viable energy source in magnetically confined fusion devices. In magnetically confined fusion plasmas, an experimental phase-space characterisation of convective and diffusive energetic particle losses induced by Alfven/acoustic waves allows for a better understanding of the underlying physics. The relevance of these results in the problem of the anomalous heating of the solar corona is checked by MHD simulations of Tokamak-like Solar flare tubes.
Hybrid Vlasov simulations for alpha particles heating in the solar wind
Authors: Perrone Denise , Valentini Francesco , Veltri Pierluigi
Published: June 2011

Heating and acceleration of heavy ions in the solar wind and corona represent a long-standing theoretical problem in space physics and are distinct experimental signatures of kinetic processes occurring in collisionless plasmas. To address this problem, we propose the use of a low-noise hybrid-Vlasov code in four dimensional phase space (1D in physical space and 3D in velocity space) configuration. We trigger a turbulent cascade injecting the energy at large wavelengths and analyze the role of kinetic effects along the development of the energy spectra. Following the evolution of both proton and α distribution functions shows that both the ion species significantly depart from the maxwellian equilibrium, with the appearance of beams of accelerated particles in the direction parallel to the background magnetic field.
Energetic Solar Electrons – Whistler Bootstrap, Magnetic Knots and Small-scale Reconnection
Authors: Roth Ilan
Published: June 2011

The (near) relativistic electrons, emanating from the solar corona in long-lasting, gradual events, are generally observed at 1 AU as delayed vs the less energetic, type-III beams. The observations are consistent with the delayed electrons being energized along the stretched post-CME coronal field lines, when the tail of an anisotropic seed population, which is injected in conjunction to the observed radioheliograph bursts, interacts with the self-excited whistler waves (bootstrap mechanism). These bursts indicate efficient processes where suprathermal seed electrons are injected as a result of magnetic reconnection at the marginally stable coronal configuration left behind the emerging CME. The dependence of the bootstrap mechanism on the electron injection raises the general question of the MHD description and its deviation over the small electron skin-depth scale. The similarity between MHD and knot theories allows one to characterize any turbulent magnetic configuration through topological invariants, while deviation over electron skin-depth scale, characterized by the generalized vorticity, which is enhanced due to density inhomogeneity, creates the conditions for the potential injection sites.
Solar flares: observations vs simulations
Authors: Rubio da Costa Fatima , Zuccarello Francesca , Labrosse Nicolas , Fletcher Lyndsay , Prosecký Tomáš , Kašparová Jana
Published: June 2011

In order to study the properties of faint, moderate and bright flares, we simulate the conditions of the solar atmosphere using a radiative hydrodynamic model (Abbett & Hawley, 1999). A constant beam of non-thermal electrons is injected at the apex of a 1D coronal loop and heating from thermal soft X-ray emission is included. We compare the results with some observational data in Ly-α (using TRACE 1216 and 1600 Å data and estimating the “pure” Ly-α emission) and in Hα (data taken with a Multichannel Flare Spectrograph, at the Ondrejov Observatory).
Magnetic helicity evolution inside a hexagonal convective cell
Authors: Smyrli Aimilia , Mackay Duncan , Zuccarello Francesca
Published: June 2011

Magnetic helicity has received considerable attention in the area of fluid dynamics. Recently, this quantity is attracting the interest of solar physicists and much research has been carried out related to magnetic helicity generation and transport through different solar layers, starting from the interior and the convection zone, towards the photosphere, the corona and finally into the heliosphere. Taking into account the global importance of supergranular cells in convection theories, we study the motion of magnetic features into such a geometrical element simplified as hexagonal cell and we analyse the results in terms of the accumulated magnetic helicity. We compute the emergence of a bipole inside the hexagonal cell and its motion from the centre of the cell towards its sides and its vertices, where the magnetic elements are considered to be sinking down. Multiple bipoles are also considered and phenomena such as cancellation, coalescence and fragmentation are also investigated. We find that the most important process for the accumulation of magnetic helicity is the shear motion between the polarities. The magnetic helicity accumulation changes its trend when one polarity reaches the side of the hexagon, and later the vertex. It has zero value when there is no shear motion inside the hexagonal cell, and it is constant when there is no shear between the two polarities during their motion along the cell sides.
Superdiffusive and ballistic propagation of protons in solar energetic particle events
Authors: Trotta Enrico M. , Zimbardo Gaetano
Published: June 2011

In this work we show that protons can exhibit both superdiffusive and ballistic propagation, at variance with standard diffusion. We carry out an analysis of impulsive solar energetic particle (SEP) events, for which the observed time profile of energetic particle fluxes represent the propagator of the corresponding transport equation. We show that in the case of superdiffusive or ballistic transport the propagator in the time asymptotic regime has a power law form, and that a fit of the observed time profiles allows to determine the transport regime. Using data obtained from ACE and SoHO spacecraft, two proton and electron events, which exhibit both superdiffusive and ballistic transport, will be shown. The finding of these anomalous regimes implies that no finite mean free path can be defined.
Electron acceleration by a wavy shock front: details on angular distribution
Authors: Vandas Marek , Karlický Marian
Published: June 2011

We studied numerically electron acceleration by a perpendicular wavy shock. Distribution function of accelerated electrons is highly anisotropic, with many sharp peaks. The peaks are caused by (usually single) reflections of electrons by the shock and subsequent transmission.
Plasma processes in pulsar magnetospheres
Authors: Melrose D. B.
Published: June 2011

It is pointed out that the standard model for pulsar electrodynamics is based on a false premise, related to neglecting the displacement current, and the associated need for current screening. Wave dispersion in the standard model is reviewed, and its relation to the interpretation of pulsar radio emission and its polarization is discussed. Inclusion of the displacement current results in large-amplitude oscillations; some of the implications of these oscillations on the interpretation of the radio emission are discussed.
Theory of quasi-stationary kinetic dynamos in magnetized accretion discs
Authors: Cremaschini Claudio , Miller John C. , Tessarotto Massimo
Published: June 2011

Magnetic fields are a distinctive feature of accretion disc plasmas around compact objects (i.e., black holes and neutron stars) and they play a decisive role in their dynamical evolution. A fundamental theoretical question related with this concerns investigation of the so-called gravitational MHD dynamo effect, responsible for the self-generation of magnetic fields in these systems. Experimental observations and theoretical models, based on fluid MHD descriptions of various types support the conjecture that accretion discs should be characterized by coherent and slowly time-varying magnetic fields with both poloidal and toroidal components. However, the precise origin of these magnetic structures and their interaction with the disc plasmas is currently unclear. The aim of this paper is to address this problem in the context of kinetic theory. The starting point is the investigation of a general class of Vlasov-Maxwell kinetic equilibria for axi-symmetric collisionless magnetized plasmas characterized by temperature anisotropy and mainly toroidal flow velocity. Retaining finite Larmor-radius effects in the calculation of the fluid fields, we show how these configurations are capable of sustaining both toroidal and poloidal current densities. As a result, we suggest the possible existence of a kinetic dynamo effect, which can generate a stationary toroidal magnetic field in the disc even without any net radial accretion flow. The results presented may have important implications for equilibrium solutions and stability analysis of accretion disc dynamics.
Stationary and axisymmetric configurations of compact stars with extremely strong and highly localized magnetic fields
Authors: Fujisawa Kotaro , Yoshida Shin'ichiro , Eriguchi Yoshiharu
Published: June 2011

Using a new formulation to compute structures of stationary and axisymmetric magnetized barotropic stars in Newtonian gravity, we have succeeded in obtaining numerically exact models of stars with extremely high interior magnetic fields. In this formulation, there appear four arbitrary functions of the magnetic flux function from the integrability conditions among the basic equations. Since in our new formulation these arbitrary functions appear in the expression of the current density, configurations with different current distributions can be specified by choosing the forms of the arbitrary functions.

By choosing appropriate forms for the four arbitrary functions, we have solved many kinds of equilibrium configurations both with poloidal and toroidal magnetic fields. Among them, by choosing special form for the toroidal current density, we have been able to obtain magnetized stars which have extremely strong poloidal magnetic fields deep inside the core region near the symmetric axis. By adopting the appropriate model parameters for the neutron stars, the magnetic fields could be 1014 ~ 1015 G on the surfaces and be about 1017 G in the deep interior regions. For other model parameters appropriate for white dwarfs, the magnetic fields could be around 107 ~ 108 G (surface regions) and 109 ~ 1010 G (core regions). It is remarkable that the regions with very strong interior magnetic fields are confined to a very narrow region around the symmetric axis in the central part of the stars. The issues of stability of these configurations and of evolutionary paths to reach such configurations need to be investigated in the future work.
Kinetic closure conditions for quasi-stationary collisionless axisymmetric magnetoplasmas
Authors: Cremaschini Claudio , Miller John C. , Tessarotto Massimo
Published: June 2011

A characteristic feature of fluid theories concerns the difficulty of uniquely defining consistent closure conditions for the fluid equations. In fact it is well known that fluid theories cannot generally provide a closed system of equations for the fluid fields. This feature is typical of collisionless plasmas where, in contrast to collisional plasmas, asymptotic closure conditions do not follow as a consequence of an H-theorem This issue is of particular relevance in astrophysics where fluid approaches are usually adopted. On the other hand, it is well known that the determination of the closure conditions is in principle achievable in the context of kinetic theory. In the case of multi-species thermal magnetoplasmas this requires the determination of the species tensor pressure and of the corresponding heat fluxes. In this paper we investigate this problem in the framework of the Vlasov-Maxwell description for collisionless axisymmetric magnetoplasmas arising in astrophysics, with particular reference to accretion discs around compact objects (like black holes and neutron stars). The dynamics of collisionless plasmas in these environments is determined by the simultaneous presence of gravitational and magnetic fields, where the latter may be both externally produced and self-generated by the plasma currents. Our starting point here is the construction of a solution for the stationary distribution function describing slowly-varying gyrokinetic equilibria. The treatment is applicable to non-relativistic axisymmetric systems characterized by temperature anisotropy and differential rotation flows. It is shown that the kinetic formalism allows one to solve the closure problem and to consistently compute the relevant fluid fields with the inclusion of finite Larmor-radius effects. The main features of the theory and relevant applications are discussed.
Ponderomotive barrier for plasma particles on the boundary of astrophysical jets
Authors: Dubinova Anna A. , Kocharovsky Vladimir V.
Published: June 2011

We study kinetics of plasma particles on internal inhomogeneities and on the boundary of astrophysical jets in the presence of intensive low-frequency electromagnetic (surface and bulk waves). These waves with energy density exceeding or of the same order as the particle kinetic energy density can be generated due to the non-equilibrium state of plasma and lead to the jet stratification at various scales. The main reason is a ponderomotive force which is able to change dramatically the particle behavior, the plasma density cross-section profile and the wave collimation. We present results obtained on the basis of our simple ponderomotive model of the self-consistent analysis of the electromagnetic wave propagation and the formation of the plasma density profile.
Magnetic collimation of relativistic jets: the role of the black hole spin
Authors: Globus N. , Sauty C. , Cayatte V.
Published: June 2011

An ideal engine for producing ultrarelativistic jets is a rapidly rotating black hole threaded by a magnetic field. Following the 3+1 decomposion of spacetime of Thorne et al. (1986), we use a local inertial frame of reference attached to an observer comoving with the frame-dragging of the Kerr black hole (ZAMO) to write the GRMHD equations. Assuming θ-self similarity, analytical solutions for jets can be found for which the streamline shape is calculated exactly. Calculating the total energy variation between a non polar streamline and the polar axis, we have extended to the Kerr metric the simple criterion for the magnetic collimation of jets developed by Sauty et al. (1999). We show that the black hole rotation induces a more efficient magnetic collimation of the jet.
ALMA and solar research
Authors: Karlický Marian , Bárta Miroslav
Published: June 2011

The ALMA (Atacama Large Millimeter/sub-millimeter Array) is the large interferometer that will consist up to 64 high-precision antennas operating in the 31.3 – 950 GHz frequency range. In this range unique observations in cosmology, cold universe, galaxies, stars and their formations, and so on are expected. Among these objectives there is a unique possibility to observe the Sun and to address outstanding issues of solar physics. The ALMA is shortly described and then the new ESO-ALMA European node (ARC) built at Ondřejov Observatory is presented. The new ARC is the only one in Europe oriented to solar physics. The requirements and limitations for ALMA solar observations, as well as some examples of possible solar-oriented ALMA projects, are mentioned.
Cosmic-ray driven dynamo in galaxies
Authors: Hanasz M. , Wóltanski D. , Kowalik K. , Kotarba H.
Published: June 2011

We present recent developments of global galactic-scale numerical models of the Cosmic Ray (CR) driven dynamo, which was originally proposed by Parker (1992). We conduct a series of direct CR+MHD numerical simulations of the dynamics of the interstellar medium (ISM), composed of gas, magnetic fields and CR components. We take into account CRs accelerated in randomly distributed supernova (SN) remnants, and assume that SNe deposit small-scale, randomly oriented, dipolar magnetic fields into the ISM. The amplification timescale of the large-scale magnetic field resulting from the CR-driven dynamo is comparable to the galactic rotation period. The process efficiently converts small-scale magnetic fields of SN-remnants into galactic-scale magnetic fields. The resulting magnetic field structure resembles the X-shaped magnetic fields observed in edge-on galaxies.
3D numerical simulations of magnetic field evolution in barred galaxies and in spiral galaxies under influence of tidal forces
Authors: Otmianowska-Mazur Katarzyna , Kulpa-Dybeł Katarzyna , Kulesza-Żydzik Barbara , Siejkowski Hubert , Kowal Grzegorz
Published: June 2011

We present the results of the three-dimensional, fully non-linear MHD simulations of the large-scale magnetic field evolution in a barred galaxy with the back reaction of magnetic field to gas. We also include the process of the cosmic-ray driven dynamo. In addition, we check what physical processes are responsible for the magnetic field evolution in the tidally influenced spiral galaxies. We solve the MHD equations for the gas and magnetic field in a spiral galaxy with gravitationally prescribed bulge, disk and halo which travels along common orbit with the second body. In order to compare our modeling results with the observations we also construct the maps of high-frequency (Faraday rotation-free) polarized radio emission from the simulated magnetic fields. The model accounts for the effects of projection and limited resolution.

We found that the obtained magnetic field configurations are highly similar to the observed maps of the polarized intensity of barred galaxies, because the modeled vectors form coherent structures along the bar and spiral arms. We also found a physical explanation of the problem of inconsistency between the velocity and magnetic fields character present in this type of galaxies. Due to the dynamical influence of the bar, the gas forms spiral waves which go radially outward. Each spiral arm forms the magnetic arm which stays much longer in the disk than the gaseous spiral structure. The modeled total energy of magnetic field and magnetic flux grows exponentially due to the action of the cosmic-ray driven dynamo. We also obtained the polarization maps of tidally influenced spiral galaxies which are similar to observations.
3D model of magnetic fields evolution in dwarf irregular galaxies
Authors: Siejkowski Hubert , Soida Marian , Otmianowska-Mazur Katarzyna , Hanasz Michał , Bomans Dominik J.
Published: June 2011

Radio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.
Simulations of astrophysical dynamos
Authors: Brandenburg Axel
Published: June 2011

Numerical aspects of dynamos in periodic domains are discussed. Modifications of the solutions by numerically motivated alterations of the equations are being reviewed using the examples of magnetic hyperdiffusion and artificial diffusion when advancing the magnetic field in its Euler potential representation. The importance of using integral kernel formulations in mean-field dynamo theory is emphasized in cases where the dynamo growth rate becomes comparable with the inverse turnover time. Finally, the significance of microscopic magnetic Prandtl number in controlling the conversion from kinetic to magnetic energy is highlighted.
Relativistic jets and current driven instabilities
Authors: Ferrari A. , Mignone A. , Campigotto M.
Published: June 2011

We review the present results on the study of the propagation of relativistic collimated outflows characteristics of active galaxies and active stars. Magnetic fields, namely their azimuthal components, gives rise to current driven instabilities whose nonlinear development can actually be connected to the complex morphologies observed in astrophysical jets.
Stationary and axisymmetric magnetized equilibria of stars and winds
Authors: Yoshida Shin , Fujisawa Kotaro , Eriguchi Yoshiharu , Yoshida Shijun , Takahashi Rohta
Published: June 2011

We present a new formulation to compute numerically stationary and axisymmetric equilibria of magnetized and self-gravitating astrophysical fluids. Under the assumption of ideal MHD, the stream function for the flow can be chosen as a basic variable with which the Euler-Maxwell equations are cast into a set of basic equations, i.e. a generalized Bernoulli equation and a Grad-Shafranov-like equation by employing various integral conditions. A novel feature of this formulation is that systems with stars, disks and winds are treated in a simple unified picture and the magnetic field structures can contain both poloidal and toroidal components.
Saturation of MRI via parasitic modes
Authors: Pessah Martin E.
Published: June 2011

Understanding the physical mechanisms that play a role in the saturation of the magnetorotational instability (MRI) has been an outstanding problem in accretion physics since the early 90's. Here, we present the summary of a study of the parasitic modes that feed off exact viscous, resistive MRI modes. We focus on the situation in which the amplitude of the magnetic field produced by the MRI is such that the instantaneous growth rate of the fastest parasitic mode matches that of the fastest MRI mode. We argue that this "saturation" amplitude provides an estimate of the magnetic field that can be generated by the MRI before the secondary instabilities suppress its growth significantly. We show that there exist two regimes, delimited by a critical Elsasser number of order unity, in which saturation is achieved via secondary instabilities that correspond to either Kelvin-Helmholtz or tearing modes.
A first model of stable magnetic configuration in stellar radiation zones
Authors: Duez Vincent , Braithwaite Jonathan , Mathis Stéphane
Published: June 2011

We test the stability of a magnetic equilibrium configuration using numerical simulations and semi-analytical tools. The tested configuration is, as described by Duez & Mathis (2010), the lowest energy state for a given helicity in a stellar radiation zone. We show using 3D magneto-hydrodynamic (MHD) simulations that the present configuration is stable with respect to all submitted perturbations, that would lead to the development of kink-type instabilities in the case of purely poloidal or toroidal fields, both well known to be unstable. We also discuss, using semi-analytic work, the stabilizing influence of one component on the other and show that the found configuration actually lies in the stability domain predicted by a linear analysis of resonant modes.
Kinetic Simulations of Type II Radio Burst Emission Processes
Authors: Ganse Urs , Spanier Felix , Vainio Rami
Published: June 2011

Using a fully relativistic, 3D particle in cell code we have studied Langmuir- and electromagnetic wave processes in a CME foreshock plasma with counterstreaming electron beams. Langmuir wave excitation in resonance with the plasma frequency is observed, with timescales in accordance with theoretical predictions. However, no three wave interaction leading to emission of electromagnetic waves were detectable within the timeframe of our simulations.
Turbulent magnetic pressure instability in stratified turbulence
Authors: Kemel K. , Brandenburg A. , Kleeorin N. , Rogachevskii I.
Published: June 2011

A reduction of total mean turbulent pressure due to the presence of magnetic fields was previously shown to be a measurable effect in direct numerical simulations. However, in the studied parameter regime the formation of large-scale structures, as anticipated from earlier mean-field simulations, was not found. An analysis of the relevant mean-field parameter dependency and the parameter domain of interest is conducted in order to clarify this apparent discrepancy.
High-order methods for the simulation of hydromagnetic instabilities in core-collapse supernovae
Authors: Rembiasz T. , Obergaulinger M. , Aloy M. Angel , Cerdá-Durán P. , Müller E.
Published: June 2011

We present an assessment of the accuracy of a recently developed MHD code used to study hydromagnetic flows in supernovae and related events. The code, based on the constrained transport formulation, incorporates unprecedented ultra-high-order methods (up to 9th order) for the reconstruction and the most accurate approximate Riemann solvers. We estimate the numerical resistivity of these schemes in tearing instability simulations.
Dynamo in the Intra-Cluster Medium: Simulation of CGL-MHD Turbulent Dynamo
Authors: Santos-Lima R. , de Gouveia Dal Pino E. M. , Lazarian A. , Kowal G. , Falceta-Gonçalves D.
Published: June 2011

The standard magnetohydrodynamic (MHD) description of the plasma in the hot, magnetized gas of the intra-cluster (ICM) medium is not adequate because it is weakly collisional. In such collisionless magnetized gas, the microscopic velocity distribution of the particles is not isotropic, giving rise to kinetic effects on the dynamical scales. These kinetic effects could be important in understanding the turbulence as well as the amplification and maintenance of the magnetic fields in the ICM. It is possible to formulate fluid models for collisonless or weakly collisional gas by introducing modifications in the MHD equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD model based on the CGL-closure, which allows the adiabatic evolution of the two components of the pressure tensor (the parallel and perpendicular components with respect to the local magnetic field), we performed 3D numerical simulations of forced turbulence in order to study the amplification of an initially weak seed magnetic field. We found that the growth rate of the magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but the magnetic energy saturates in a level smaller than that of the MHD case. We also found that a necessary condition for the dynamo to operate is to impose constraints on the anisotropy of the pressure.
Prenatal exposure to hyperemesis gravidarum linked to increased risk of psychological and behavioral disorders in adulthood
Authors: Mullin P. M. , Bray A. , Schoenberg F. , MacGibbon K. W. , Romero R. , Goodwin T. M. , Fejzo M. S.
Published: June 2011

Hyperemesis gravidarum (HG), severe nausea and vomiting of pregnancy, is characterized by long-term maternal stress, undernutrition and dehydration. While maternal stress and malnutrition of pregnancy are linked to poor neonatal outcome and associated with poor adult health, long-term outcome of fetal exposure to HG has never been explored. The purpose of this study is to determine whether long-term emotional and behavioral diagnoses may be associated with fetal exposure to HG. Emotional and behavioral diagnoses of adults born of a pregnancy complicated by HG were compared to diagnoses from non-exposed controls. Offspring exposed to HGin uterowere significantly more likely to have a psychological and behavioral disorder (OR = 3.6,P< 0.0001) with diagnoses primarily of depression, bipolar disorder and anxiety.In uteroexposure to HG may lead to increased risks of psychological and behavioral disorders in the offspring.
Developing a GPS TEC mapping service over Canada
Authors: Ghoddousi‐Fard Reza , Héroux Pierre , Danskin Donald , Boteler David
Published: June 2011

Understanding space weather phenomena in near real time can be challenging without the proper access to data sources. Space weather nowcasts and forecasts require timely dissemination of products relevant to end‐users. A process has been developed to routinely map total electron content (TEC) estimated from GPS observations over Canada. This technique implements spherical cap harmonic analysis to interpolate vertical estimates on a standardized mapping grid that can be compared with other types of data to understand the evolution of processes in the ionosphere. The service can also provide an estimate of positioning errors encountered by Global Navigation Satellite Systems users that are associated with ionospheric TEC.
BBSRC Data Sharing Policy
Authors: Collis Amanda , McAllister David , Ball Michael
Published: June 2011

BBSRC recognizes the importance of contributing to the growing international efforts in data sharing. BBSRC is committed to getting the best value for the funds we invest and believes that making research data more readily available will reinforce open scientific inquiry and stimulate new investigations and analyses. BBSRC supports the view that data sharing should be led by the scientific community and driven by scientific need. It should also be cost effective and the data shared should be of the highest quality. Members of the community are expected and encouraged to practice and promote data sharing, determine standards and best practice, and create a scientific culture in which data sharing is embedded.
Supervision: Self-Assessment in Supervision: The Use of the Rubric as a Means of Self-Assessment
Authors: Wright Janice
Published: June 2011

Self-assessment in supervision is a complex task; therefore, using a rubric as a means of self-assessment may be a valuable tool. This article will discuss the development of a rubric using the Knowledge and Skills Needed by Speech-Language Pathologists Providing Clinical Supervision (American Speech-Language-Hearing Association [ASHA], 2008a) as the foundation of the tool. The proposed rubric can serve as a tool to self-assess skills and professional development needs in the area of clinical supervision. ASHA has outlined 11 competencies required by supervisors of students and Clinical Fellows (CFs) in the field of speech-language pathology (2008a). Using these competencies paired with a rubric model proposed by Arrasmith and Galion (2001), this article will provide a means by which clinical supervisors can guide their professional development in supervision.
Conducting Dysphagia Research in the Field Through Partnerships With Clinicians
Authors: Steele Catriona M.
Published: June 2011

Research studies that involve collaborations between scientists and frontline clinicians provide rich opportunities for advancing knowledge in the field of dysphagia. However, various challenges exist in bridging research goals and clinical priorities. In this article, we explore the perspectives of those who have participated in previous collaborations to gain insights regarding the challenges, surprises, and benefits of such collaboration.
Building a Better Bridge From Research to Practice: What's in Your Toolbox?
Authors: Swigert Nancy B.
Published: June 2011

Clinicians understand the importance of practicing from an evidence base, but face challenges when trying to do so. Some of these challenges must be solved by the clinician (e.g., lack of time to read the articles, lack of expertise in analyzing the quality of the research). However, the responsibility does not lie solely with the clinician. All involved in producing research bear some responsibility in bridging the research to practice gap.
Technology as a Language Tool: Augmentative and Alternative Communication in the Classroom
Authors: Kent-Walsh Jennifer , Binger Cathy
Published: June 2011

As evidenced across the articles in this issue of Perspectives, the modern classroom includes a range of technologies that afford educators, students, and families more ways to engage and communicate than many of us ever could have imagined. One group for which the technological revolution has had a particularly obvious effect in the school environment has been with students who are not able to meet all of their communication needs using natural speech. Students requiring the use of augmentative and alternative communication (AAC) have enjoyed an exponential increase in options for communicating in all relevant environments, including the classroom. School-based speech-language pathologists (SLPs) possess a range of skills that allows them to help facilitate functional use of AAC technologies in the classroom environment. Given that AAC technologies are language tools, SLPs can employ their expertise in language to implement relevant goals, objectives, and interventions for children with AAC needs. To illustrate this point, an AAC case study is presented along with sample goals and interventions that may be used in the school setting.
Online Fluency Disorders Resources for School-Based Clinicians
Authors: Kuster Judith Maginnis
Published: June 2011

Speech-language clinicians working in a school setting are some of the busiest people I know. They see a full caseload of children with a variety of communication disorders, keep data for each session, schedule diagnostic sessions, plan and prepare for therapy, meet with parents and school staff, deal with tons of paperwork (IEPs, reports, maybe billing for services), pore over catalogs to order supplies, register for continuing education to maintain licensure and certification, serve on committees, and sometimes even help with lunch room and playground duty. Added to all of that is a requirement in IDEA to provide “evidence-based” services.
Experimental investigation of interaction of very low frequency electromagnetic waves with metallic nanostructure
Authors: Nalladega Vijay , Sathish Shamachary , Murray Terry , Shin Eunsung , Jata Kumar V. , Blodgett M. P.
Published: June 2011

The interaction of low-frequency electromagnetic waves with metallic nanostructure consisting of nanoparticles has been investigated. The existence of helicons in metallic nanostructure is predicted based on the enhancement of effective mass of the electrons in metallic mesostructures in low-frequency electromagnetic field. The enhancement of the effective mass of electrons subjected to low-frequency electromagnetic field results in the suppression of the cyclotron frequency. When the excitation frequency approaches the cyclotron frequency, helicons can be observed, which in typical metals occur at MHz frequencies. With the decrease in the cyclotron frequency in nanostructures, the helicons can be observed at low frequencies. We present an experimental setup to detect and image helicon resonances in metallic nanostructures at low frequencies and room temperature conditions. The approach is based on modifying an existing atomic force microscope to image surface topography and the magnetic field images of helicon waves simultaneously in metallic nanoparticles. The magnetic field images of the helicon waves and different resonance modes are presented for platinum nanoparticles deposited using through thin film ablation. The contrast in the magnetic field images is explained based on the generation of resonance modes due to helicon wave propagation in the nanostructure. The features in the helicon resonance images are examined as a function of the particle size and frequency of the electromagnetic wave.