bluuebunny/crossref_metadata_2025_split huggingface dataset:
Realistic MHD simulations of magnetic self-organization in solar plasma
Authors: Kitiashvili I. N. , Kosovichev A. G. , Wray A. A. , Mansour N. N. 
Published: June 2011

AbstractFilamentary structure is a fundamental property of the magnetized solar plasma. Recent high-resolution observations and numerical simulations have revealed close links between the filamentary structures and plasma dynamics in large-scale solar phenomena, such as sunspots and magnetic network. A new emerging paradigm is that the mechanisms of the filamentary structuring and large-scale organization are natural consequences of turbulent magnetoconvection on the Sun. We present results of 3D radiative MHD large-eddy simulations (LES) of magnetic structures in the turbulent convective boundary layer of the Sun. The results show how the initial relatively weak and uniformly distributed magnetic field forms the filamentary structures, which under certain conditions gets organized on larger scales, creating stable long-living magnetic structures. We discuss the physics of magnetic self-organization in the turbulent solar plasma, and compare the simulation results with observations.
Cross helicity in stellar magnetoconvection
Authors: Küker Manfred , Rüdiger Günther 
Published: June 2011

AbstractMagnetic diffusion is a key ingredient in mean-field dynamo models but neither observations nor theory are able to produce reliable values. Numerical simulations provide an alternative way to determine the turbulent electromotive force. Cross helicity allows us to determine the turbulent magnetic diffusion coefficient in simulations of stellar magnetoconvection.
Spatio-temporal variability of the photospheric magnetic field
Authors: Vecchio A. , Laurenza M. , Meduri D. , Carbone V. , Storini M. 
Published: June 2011

AbstractThe spatio-temporal dynamics of the solar magnetic field has been investigated by using NSO/Kitt Peak synoptic magnetic maps covering ~28 yr. For each heliographic latitude the field has been analyzed through the Empirical Mode Decomposition, in order to investigate the time evolution of the various characteristic oscillating frequencies. Preliminary results are discussed.
Special relativistic magnetohydrodynamic simulation of two-component outflow powered by magnetic explosion on compact stars
Authors: Matsumoto Jin , Masada Youhei , Asano Eiji , Shibata Kazunari 
Published: June 2011

AbstractThe nonlinear dynamics of the outflow driven by magnetic explosion on the surface of compact object is investigated through special relativistic magnetohydrodynamic simulations. We adopt, as an initial equilibrium state, a spherical stellar object embedded in the hydrostatic plasma which has a density ρ(r) ∝ r−α and is threaded by a dipole magnetic field. The injection of magnetic energy at the surface of compact star breaks the dynamical equilibrium and triggers two-component outflow. At the early evolutionary stage, the magnetic pressure increases rapidly in time around the stellar surface, initiating a magnetically driven outflow. Then it excites a strong forward shock, shock driven outflow. The expansion velocity of the magnetically driven outflow is characterized by the Alfvén velocity on the stellar surface, and follows a simple scaling relation υmag ∝ υA1/2. When the initial density profile declines steeply with radius, the strong shock is accelerated self-similarly to relativistic velocity ahead of the magnetically driven component. We find that the evolution of the strong forward shock can be described by a self-similar relation Γsh ∝ rsh, where Γsh is the Lorentz factor of the plasma measured at the shock surface rsh. It should be stressed that the pure hydrodynamic process is responsible for the acceleration of the shock driven outflow. Our two-component outflow model, which is the natural outcome of the magnetic explosion, would deepen the understanding of the magnetic active phenomena on various magnetized stellar objects.
Electromagnetic emission by subsequent processes L→L'+S and L+L'→T
Authors: Karlický Marian , Bárta Miroslav 
Published: June 2011

AbstractUsing a 2.5-D electromagnetic particle-in-cell (PIC) model, very early stages of a generation of the electromagnetic emission produced by a monochromatic Langmuir wave are studied. It is found that the electromagnetic emission, which is dominant on the harmonic of the plasma frequency, starts to be generated in a very small region of k-vectors. Later on the k-vectors of this emission are scattered around a ‘circle’ (in our 2-D case), given by the relations for the L+L'→T process. Analytical analysis of two subsequent processes L→L'+S a L+L'→T confirms these results.
New interactive solar flare modeling and advanced radio diagnostics tools
Authors: Fleishman Gregory D. , Nita Gelu M. , Gary Dale E. 
Published: June 2011

AbstractThe coming years will see routine use of solar data of unprecedented spatial and spectral resolution, time cadence, and completeness in the wavelength domain. To capitalize on the soon to be available radio facilities such as the expanded OVSA, SSRT and FASR, and the challenges they present in the visualization and synthesis of the multi-frequency datasets, we propose that realistic, sophisticated 3D active region and flare modeling is timely now and will be a forefront of coronal studies over the coming years. Here we summarize our 3D modeling efforts, aimed at forward fitting of imaging spectroscopy data, and describe currently available 3D modeling tools. We also discuss plans for future generalization of our modeling tools.
Solar wind turbulence: Advances in observations and theory
Authors: Podesta J. J. 
Published: June 2011

AbstractObservations of plasma and magnetic field fluctuations in the solar wind provide a valuable source of information for the study of turbulence in collisionless astrophysical plasmas. Scientific data collected by various spacecraft over the last few decades has fueled steady progress in this field. Theoretical models, numerical simulations, and comparisons between theory and experiment have also contributed greatly to these advances. This review highlights some recent advances on the observational side including measurements of the anisotropy of inertial range fluctuations as revealed by the different scaling laws parallel and perpendicular to the mean magnetic field, measurements of the normalized cross-helicity spanning the entire inertial range which demonstrate that this quantity is scale invariant, and improved measurements of the spectrum of magnetic field fluctuations in the dissipation range that show a spectral break near the lengthscale of the electron gyro-radius. The theoretical implications of these results and comparisons between theory and observations are briefly summarized.
Magnetism in galaxies – Observational overview and next generation radio telescopes
Authors: Beck Rainer 
Published: June 2011

AbstractThe strength and structure of cosmic magnetic fields is best studied by observations of radio continuum emission, its polarization and its Faraday rotation. Fields with a well-ordered spiral structure exist in many types of galaxies. Total field strengths in spiral arms and bars are 20–30 μG and dynamically important. Strong fields in central regions can drive gas inflows towards an active nucleus. The strongest regular fields (10–15 μG) are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. The typical degree of polarization is a few % in spiral arms, but high (up to 50%) in interarm regions. The detailed field structures suggest interaction with gas flows. Faraday rotation measures of the polarization vectors reveals large-scale patterns in several spiral galaxies which are regarded as signatures of large-scale (coherent) fields generated by dynamos. – Polarization observations with the forthcoming large radio telescopes will open a new era in the observation of magnetic fields and should help to understand their origin. Low-frequency radio synchrotron emission traces low-energy cosmic ray electrons which can propagate further away from their origin. LOFAR (30–240 MHz) will allow us to map the structure of weak magnetic fields in the outer regions and halos of galaxies, in galaxy clusters and in the Milky Way. Polarization at higher frequencies (1–10 GHz), to be observed with the EVLA, MeerKAT, APERTIF and the SKA, will trace magnetic fields in the disks and central regions of galaxies in unprecedented detail. All-sky surveys of Faraday rotation measures towards a dense grid of polarized background sources with ASKAP and the SKA are dedicated to measure magnetic fields in distant intervening galaxies and clusters, and will be used to model the overall structure and strength of the magnetic field in the Milky Way.
On the solution of the Kompaneets equation in cosmological context: a numerical code to predict the CMB spectrum under general conditions
Authors: Burigana C. , Procopio P. , De Rosa A. 
Published: June 2011

AbstractInterpretation of current and future data calls for a continuous improvement in the theoretical modeling of CMB spectrum. We describe the new version of a numerical code, KYPRIX, specifically written to solve the Kompaneets equation in a cosmological context under general assumptions. We report on the equation formalism, and structure and computational aspects of the code. New physical options have been introduced in the current code version: the cosmological constant in the terms controlling the general expansion of the Universe, the relevant chemical abundances, and the ionization history, from recombination to cosmological reionization. We present some of fundamental tests we carried out to verify the accuracy, reliability, and performance of the code. All the tests demonstrate the reliability and versatility of the new code version and its accuracy and applicability to the scientific analysis of current CMB spectrum data and of much more precise measurements that will be available in the future.
An XMM-Newton view of a small sample of Seyfert, 1 Galaxies
Authors: Cardaci M. V. , Hagele G. F. , Santos-Lleó M. , Krongold Y. , Díaz A. I. , Rodriguez-Pascual P. 
Published: June 2011

AbstractWe present a detailed analysis of all the X-ray data taken by the XMM-Newton satellite of a small sample of five Seyfert 1 galaxies: ESO 359-G19, HE 1143-1810, CTS A08.12, Mkn 110, and UGC 11763. Our aim is to characterize the different components of the material that print the absorption and emission features in the X-ray spectra of these objects. The continuum emission was studied through the EPIC spectra taking advantage of the spectral range of these cameras. The high resolution RGS spectra were analyzed in order to characterize the absorbing features and the emission line features that arise in the spectra of these sources.
How can vorticity be produced in irrotationally forced flows?
Authors: Sordo Fabio Del , Brandenburg Axel 
Published: June 2011

AbstractA spherical hydrodynamical expansion flow can be described as the gradient of a potential. In that case no vorticity should be produced, but several additional mechanisms can drive its production. Here we analyze the effects of baroclinicity, rotation and shear in the case of a viscous fluid. Those flows resemble what happens in the interstellar medium. In fact in this astrophysical environment supernovae explosion are the dominant flows and, in a first approximation, they can be seen as spherical. One of the main difference is that in our numerical study we examine only weakly supersonic flows, while supernovae explosions are strongly supersonic.
Numerical study of jets produced by conical wire arrays on the Magpie pulsed power generator
Authors: Bocchi Matteo , Chittenden Jerry P. , Ciardi Andrea , Suzuki-Vidal Francisco , Hall Gareth N. , de Grouchy Phil , Lebedev Sergei V. , Bott Simon C. 
Published: June 2011

AbstractWith the aim to model jets produced by conical wire arrays on the MAGPIE generator, and to strengthen the link between laboratory and astrophysical jets, we performed three-dimensional magneto-hydro-dynamic numerical simulations using the code GORGON and successfully reproduced the experiments. We found that a minimum resolution of ~100 μm is required to retrieve the unstable character of the jet. Moreover, arrays with less wires produce more unstable jets with stronger magnetic fields around them.
Magnetic field amplification by relativistic shocks in a turbulent medium
Authors: Mizuno Yosuke , Pohl Martin , Niemiec Jacek , Zhang Bing , Nishikawa Ken-Ichi , Hardee Philip E. 
Published: June 2011

AbstractWe perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneities, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in our two-dimensional simulations. The magnetic energy spectrum is flatter than Kolmogorov and indicates that a so-called small-scale dynamo is operating in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field.
3D turbulent reconnection driven current-sheet dynamics: solar applications
Authors: Bettarini Lapo , Lapenta Giovanni 
Published: June 2011

AbstractWe provide a complete three-dimensional picture of the reconnecting dynamics of a current-sheet. Recently, a two-dimensional non-steady reconnection dynamics has been proved to occur without the presence of any anomalous effect (Lapenta, 2008, Skender & Lapenta, 2010, Bettarini & Lapenta, 2010) but such a picture must be confirmed in a full three-dimensional configuration wherein all instability modes are allowed to drive the evolution of the system, i.e. to sustain a reconnection dynamics or to push the system along a different instability path. Here we propose a full-space analysis allowing us to determine the longitudinal and, possibly, the transversal modes driving the different current-sheet disruption regimes, the corresponding characteristic time-scales and to study system's instability space- parameter (plasma beta, Lundquist and Reynolds numbers, system's aspect ratio). The conditions leading to an explosive evolution rather then to a diffusive dynamics as well as the details of the reconnection inflow/outflow regime at the disruption phase are determined. Such system embedded in a solar-like environment and undergoing a non-steady reconnection evolution may determine the formation both of jets and waves influencing the dynamics and energetic of the upper layers and of characteristic down-flows as observed in the low solar atmosphere.
Electronic Memorandum Decreases Unnecessary Antimicrobial Use for Asymptomatic Bacteriuria and Culture-Negative Pyuria
Authors: Linares Leslie A. , Thornton David J. , Strymish Judith , Baker Errol , Gupta Kalpana 
Published: June 2011

Objectives.Asymptomatic bacteriuria/candidiuria (ASB) and culture-negative pyuria (CNP) are common and often result in inappropriate antibiotic use. We aimed to evaluate whether a standardized educational memorandum could reduce antimicrobial utilization for ASB/CNP.Design, Setting, and Patients.Quasi-experimental study with a control group, from a convenience sample of inpatients with abnormal urinalysis or urine culture results in a Veterans Affairs hospital.Intervention.An educational memorandum outlining guidelines for diagnosis and treatment of ASB was placed in the chart of patients with ASB/CNP who were receiving antimicrobials.Methods.The records of patients meeting inclusion criteria were abstracted for demographics, comorbidities, antimicrobials, and symptoms suggestive of possible urinary tract infection (UTI). Patients were categorized as having ASB, CNP, or UTI. The number of antimicrobial-days attributed to ASB/CNP was compared between the control group and the intervention group.Results.Charts of 301 patients with abnormal urine results were reviewed. Thirty of 117 (26%) patients in the control group received antimicrobials for ASB/CNP for an average of 6.3 days. In the intervention group, 24 of 92 (26%) patients received antimicrobials for ASB/CNP for an average of 2.2 days (t-test: P<.001). Adverse events from antimicrobials for ASB/CNP occurred in 3 of the 30 (10%) patients in the control group. There were no adverse events from untreated ASB/CNP in the intervention group.Conclusions.ASB and CNP resulted in antimicrobial exposure in more than one-quarter of our study patients. Placing a standardized memorandum in the electronic record was associated with a 65% relative reduction in antimicrobial-days for ASB and CNP.
Arithmetic theory of harmonic numbers
Authors: Sun Zhi-Wei 
Published: June 2011

Harmonic numbers

H

k

=

∑

0
>
j
⩽
k

1

/

j

(
k
=
0
,
1
,
2
,
…
)

H_{k}=\sum _{0>j\leqslant k}1/j\ (k=0,1,2,\ldots )

play important roles in mathematics. In this paper we investigate their arithmetic properties and obtain various basic congruences. Let

p
>
3

p>3

be a prime. We show that

∑

k
=
1

p
−
1

H

k

k

2

k

≡
0

(

m
o
d

p
)
,

∑

k
=
1

p
−
1

H

k

2

≡
2
p
−
2

(

m
o
d

p

2

)
,

∑

k
=
1

p
−
1

H

k

3

≡
6

(

m
o
d

p
)
,

\begin{equation*} \sum _{k=1}^{p-1}\frac {H_{k}}{k2^{k}}\equiv 0\ (\mathrm {mod} \ p),\ \sum _{k=1}^{p-1}H_{k}^{2} \equiv 2p-2\ (\mathrm {mod} \ p^{2}), \ \sum _{k=1}^{p-1}H_{k}^{3}\equiv 6\ (\mathrm {mod} \ p),\end{equation*}

and

∑

k
=
1

p
−
1

H

k

2

k

2

≡
0

(

m
o
d

p
)

provided

p
>
5.

\begin{equation*} \sum _{k=1}^{p-1}\frac {H_{k}^{2}}{k^{2}}\equiv 0\ (\mathrm {mod} \ p)\qquad \text {provided }\ p>5. \end{equation*}

(In contrast, it is known that

∑

k
=
1

∞

H

k

/

(
k

2

k

)
=

π

2

/

12

\sum _{k=1}^{\infty }H_{k}/(k2^{k})=\pi ^{2}/12

and

∑

k
=
1

∞

H

k

2

/

k

2

=
17

π

4

/

360

\sum _{k=1}^{\infty }H_{k}^{2}/k^{2}=17\pi ^{4}/360

.) Our tools include some sophisticated combinatorial identities and properties of Bernoulli numbers.
Perineural Dexmedetomidine Added to Ropivacaine for Sciatic Nerve Block in Rats Prolongs the Duration of Analgesia by Blocking the Hyperpolarization-activated Cation Current
Authors: Brummett Chad M. , Hong Elizabeth K. , Janda Allison M. , Amodeo Francesco S. , Lydic Ralph 
Published: June 2011

Background
The current study was designed to test the hypothesis that the increased duration of analgesia caused by adding dexmedetomidine to local anesthetic results from blockade of the hyperpolarization-activated cation (I(h)) current.

Methods
In this randomized, blinded, controlled study, the analgesic effects of peripheral nerve blocks using 0.5% ropivacaine alone or 0.5% ropivacaine plus dexmedetomidine (34 μM or 6 μg/kg) were assessed with or without the pretreatment of α(1)- and α(2)-adrenoceptor antagonists (prazosin and idazoxan, respectively) and antagonists and agonists of the I(h) current (ZD 7288 and forskolin, respectively). Sciatic nerve blocks were performed, and analgesia was measured by paw withdrawal latency to a thermal stimulus every 30 min for 300 min postblock.

Results
The analgesic effect of dexmedetomidine added to ropivacaine was not reversed by either prazosin or idazoxan. There were no additive or attenuated effects from the pretreatment with ZD 7288 (I(h) current blocker) compared with dexmedetomidine added to ropivacaine. When forskolin was administered as a pretreatment to ropivacaine plus dexmedetomidine, there were statistically significant reductions in duration of analgesia at time points 90-180 min (P < 0.0001 for each individual comparison). The duration of blockade for the forskolin (768 μM) followed by ropivacaine plus dexmedetomidine group mirrored the pattern of the ropivacaine alone group, thereby implying a reversal effect.

Conclusion
Dexmedetomidine added to ropivacaine caused approximately a 75% increase in the duration of analgesia, which was reversed by pretreatment with an I(h) current enhancer. The analgesic effect of dexmedetomidine was not reversed by an α(2)-adrenoceptor antagonist.
Rapid, Organ-Specific Transcriptional Responses to Light Regulate Photomorphogenic Development in Dicot Seedlings
Authors: Li Ying , Swaminathan Kankshita , Hudson Matthew E. 
Published: June 2011

Abstract
The dicotyledon seedling undergoes organ-specific photomorphogenic development when exposed to light. The cotyledons open and expand, the apical hook opens, and the hypocotyl ceases to elongate. Using the large and easily dissected seedlings of soybean (Glycine max ‘Williams 82’), we show that genes involved in photosynthesis and its regulation dominate transcripts specific to the cotyledon, even in etiolated seedlings. Genes for cell wall biosynthesis and metabolism are expressed at higher levels in the hypocotyl, while examination of genes expressed at higher levels in the hook region (including the shoot apical meristem) reveals genes involved in cell division and protein turnover. The early transcriptional events in these three organs in response to a 1-h treatment of far-red light are highly distinctive. Not only are different regulatory genes rapidly regulated by light in each organ, but the early-responsive genes in each organ contain a distinctive subset of known light-responsive cis-regulatory elements. We detected specific light-induced gene expression for the root phototropism gene RPT2 in the apical hook and also phenotypes in Arabidopsis (Arabidopsis thaliana) rpt2 mutants demonstrating that the gene is necessary for normal photomorphogenesis in the seedling apex. Significantly, expression of the RPT2 promoter fused to a β-glucuronidase reporter gene shows differential expression across the hook region. We conclude that organ-specific, light-responsive transcriptional networks are active early in photomorphogenesis in the aerial parts of dicotyledon seedlings.