bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic closure conditions for quasi-stationary collisionless axisymmetric magnetoplasmas
Authors: Cremaschini Claudio , Miller John C. , Tessarotto Massimo 
Published: June 2011

AbstractA 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

AbstractWe 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

AbstractAn 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

AbstractThe 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

AbstractWe 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

AbstractWe 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

AbstractRadio 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

AbstractNumerical 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

AbstractWe 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

AbstractWe 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

AbstractUnderstanding 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

AbstractWe 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

AbstractUsing 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

AbstractA 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

AbstractWe 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

AbstractThe 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.
BBSRC Data Sharing Policy
Authors: Collis Amanda , McAllister David , Ball Michael 
Published: June 2011

AbstractBBSRC 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.
Small ball probability estimates for log-concave measures
Authors: Paouris Grigoris 
Published: June 2011

We establish a small ball probability inequality for isotropic

log
\log

-concave probability measures: there exist absolute constants

c

1

,

c

2

>
0

c_{1}, c_{2}>0

such that if

X
X

is an isotropic

log
\log

-concave random vector in

R

n

{\mathbb R}^n

with

ψ

2

\psi _{2}

constant and bounded by

b
b

and if

A
A

is a non-zero

n
×
n

n\times n

matrix, then for every

ε
∈
(
0
,

c

1

)

\varepsilon \in (0,c_{1})

and

y
∈

R

n

y \in \mathbb R^n

,
\[

P

(
‖
A
x
−
y

‖

2

≤
ε
‖
A

‖

HS

)

≤

ε

(

c

2

b

‖
A

‖

HS

‖
A

‖

op

)

2

,

\mathbb P \left ( \|Ax-y\|_{2} \leq \varepsilon \|A\|_{\textrm {HS}} \right ) \leq \varepsilon ^{\big ( \frac {c_{2}}{b}\frac {\|A\|_{\textrm {HS}}}{\|A\|_{\textrm {op}}} \big )^{2} },

\]
where

c

1

,

c

2

>
0

c_{1}, c_{2}>0

are absolute constants.
Parameters Affecting Telomere-Mediated Chromosomal Truncation inArabidopsis
Authors: Nelson Andrew D. , Lamb Jonathan C. , Kobrossly Pierre S. , Shippen Dorothy E. 
Published: June 2011

AbstractConversion of a double-strand break into a telomere is a dangerous, potentially lethal event. However, little is known about the mechanism and control of de novo telomere formation (DNTF). DNTF can be instigated by the insertion of a telomere repeat array (TRA) into the host genome, which seeds the formation of a new telomere, resulting in chromosome truncation. Such events are rare and concentrated at chromosome ends. Here, we introduce tetraploid Arabidopsis thaliana as a robust genetic model for DNTF. Transformation of a 2.6-kb TRA into tetraploid plants resulted in a DNTF efficiency of 56%, fivefold higher than in diploid plants and 50-fold higher than in human cells. DNTF events were recovered across the entire genome, indicating that genetic redundancy facilitates recovery of DNTF events. Although TRAs as short as 100 bp seeded new telomeres, these tracts were unstable unless they were extended above a 1-kb size threshold. Unexpectedly, DNTF efficiency increased in plants lacking telomerase, and DNTF rates were lower in plants null for Ku70 or Lig4, components of the nonhomologous end-joining repair pathway. We conclude that multiple competing pathways modulate DNTF, and that tetraploid Arabidopsis will be a powerful model for elucidating the molecular details of these processes.
Transcriptional Programming and Functional Interactions within the Phytophthora sojae RXLR Effector Repertoire
Authors: Wang Qunqing , Han Changzhi , Ferreira Adriana O. , Yu Xiaoli , Ye Wenwu , Tripathy Sucheta , Kale Shiv D. , Gu Biao , Sheng Yuting , Sui Yangyang , Wang Xiaoli , Zhang Zhengguang , Cheng Baoping , Dong Suomeng , Shan Weixing , Zheng Xiaobo , Dou Daolong , Tyler Brett M. , Wang Yuanchao 
Published: June 2011

Abstract
The genome of the soybean pathogen Phytophthora sojae contains nearly 400 genes encoding candidate effector proteins carrying the host cell entry motif RXLR-dEER. Here, we report a broad survey of the transcription, variation, and functions of a large sample of the P. sojae candidate effectors. Forty-five (12%) effector genes showed high levels of polymorphism among P. sojae isolates and significant evidence for positive selection. Of 169 effectors tested, most could suppress programmed cell death triggered by BAX, effectors, and/or the PAMP INF1, while several triggered cell death themselves. Among the most strongly expressed effectors, one immediate-early class was highly expressed even prior to infection and was further induced 2- to 10-fold following infection. A second early class, including several that triggered cell death, was weakly expressed prior to infection but induced 20- to 120-fold during the first 12 h of infection. The most strongly expressed immediate-early effectors could suppress the cell death triggered by several early effectors, and most early effectors could suppress INF1-triggered cell death, suggesting the two classes of effectors may target different functional branches of the defense response. In support of this hypothesis, misexpression of key immediate-early and early effectors severely reduced the virulence of P. sojae transformants.
The effectiveness of an early parenting intervention for mothers with infants with sleep and settling concerns: a prospective non‐equivalent before‐after design
Authors: Hauck Yvonne L , Hall Wendy A , Dhaliwal Satvinder S , Bennett Elaine , Wells Gail 
Published: June 2011

Aim.  The study aim was to compare changes in maternal confidence, competence, depression, anxiety and settling behaviours and children’s sleep and settling behaviours for mothers and infants (4–6 months of age) attending a Day Stay intervention at an early parenting centre in Western Australia and a community group.Background.  Infant difficulties in getting to sleep and frequent night waking are concerns for parents. Techniques are available to assist parents with infants exhibiting behavioural sleep problems; however, parents often lack confidence to consistently initiate sleep interventions.Design.  The study incorporated a prospective non‐equivalent before‐after design.Method.  The conceptual framework guiding this intervention emphasised the development of parental confidence and competence through connection with practitioners to promote change. Both groups provided baseline data (time 1) and four weeks postbaseline (time 2). Recruitment occurred between July 2007–July 2009.Results.  The Ngala group (n = 93) and community group (n = 85) were not equivalent for infant age and maternal parity; there were more multiparous mothers in the community group, with infants on average one week older. The Ngala group, the majority of which were primiparous women, had significantly higher levels of competence and confidence four weeks following their Day Stay visit. There were no significant differences between groups at time 2 for time to settle the infant at night, infant night waking and maternal depression and anxiety scores.Conclusions.  Although both groups demonstrated an improvement in depression and anxiety scores, with decreased sleep and settling concerns, the results indicate parental inconsistency in settling approaches. Given links between inconsistent infant settling approaches and infants’ difficulty with sleep self‐initiation, further exploration is warranted.Relevance to clinical practice.  The conceptual framework guiding the Ngala practitioners was effective in developing confidence and competence for the sample.