2,870 research outputs found
Fast magnetic reconnection in the plasmoid-dominated regime
A conceptual model of resistive magnetic reconnection via a stochastic
plasmoid chain is proposed. The global reconnection rate is shown to be
independent of the Lundquist number. The distribution of fluxes in the
plasmoids is shown to be an inverse square law. It is argued that there is a
finite probability of emergence of abnormally large plasmoids, which can
disrupt the chain (and may be responsible for observable large abrupt events in
solar flares and sawtooth crashes). A criterion for the transition from
magnetohydrodynamic to collisionless regime is provided.Comment: 4 pages, 1 figur
Two-scale structure of the electron dissipation region during collisionless magnetic reconnection
Particle in cell (PIC) simulations of collisionless magnetic reconnection are
presented that demonstrate that the electron dissipation region develops a
distinct two-scale structure along the outflow direction. The length of the
electron current layer is found to decrease with decreasing electron mass,
approaching the ion inertial length for a proton-electron plasma. A surprise,
however, is that the electrons form a high-velocity outflow jet that remains
decoupled from the magnetic field and extends large distances downstream from
the x-line. The rate of reconnection remains fast in very large systems,
independent of boundary conditions and the mass of electrons.Comment: Submitted to Physical Review Letters, 4 pages, 4 figure
Rhetoric in the language of real estate marketing
“Des. Res.”, “rarely available”, “viewing essential” – these are all part of the peculiar parlance of housing advertisements which contain a heady mix of euphemism, hyperbole and superlative. Of interest is whether the selling agent’s penchant for rhetoric is spatially uniform or whether there are variations across the urban system. We are also interested in how the use of superlatives varies over the market cycle and over the selling season. For example, are estate agents more inclined to use hyperbole when the market is buoyant or when it is flat, and does it matter whether a house is marketed in the summer or winter? This paper attempts to answer these questions by applying textual analysis to a unique dataset of 49,926 records of real estate transactions in the Strathclyde conurbation over the period 1999 to 2006. The analysis opens up a new avenue of research into the use of real estate rhetoric and its interaction with agency behaviour and market dynamics
Fast and slow two-fluid magnetic reconnection
We present a two-fluid magnetohydrodynamics (MHD) model of quasi-stationary,
two-dimensional magnetic reconnection in an incompressible plasma composed of
electrons and ions. We find two distinct regimes of slow and fast reconnection.
The presence of these two regimes can provide a possible explanation for the
initial slow build up and subsequent rapid release of magnetic energy
frequently observed in cosmic and laboratory plasmas.Comment: 16 pages, 2 figures, 1 tabl
Very preterm infants engage in an intervention to train their control of attention: results from the feasibility study of the Attention Control Training (ACT) randomised trial
Background
Very premature birth (gestational age between 28 and 31 + 6 weeks) is associated with increased risk of cognitive delay and attention deficit disorder, which have been linked to anomalies in the development of executive functions (EFs) and their precursors. In particular, very preterm (VP) infants display anomalies in controlling attention and gathering task-relevant information. Early interventions that support attention control may be pivotal in providing a secure base for VP children’s later attainments. The Attention Control Training (ACT) is a cognitive training intervention that targets infants’ abilities to select visual information according to varying task demands but had not been tested in VP infants. We conducted a feasibility study to test the processes we intend to use in a trial delivering the ACT to VP infants.
Methods and design
We tested recruitment and retention of VP infants and their families in a randomised trial, as well as acceptability and completion of baseline and outcome measures. To evaluate these aims, we used descriptive quantitative statistics and qualitative methods to analyse feedback from infants’ caregivers. We also investigated the quality of eye-tracking data collected and indicators of infants’ engagement in the training, using descriptive statistics.
Results
Twelve VP infants were recruited, and 10 (83%) completed the study. Participants’ parents had high education attainment. The rate of completion of baseline and outcome measures was optimal. VP infants demonstrated engagement in the training, completing on average 84 min of training over three visits, and displaying improved performance during this training. Eye-tracking data quality was moderate, but this did not interfere with infants’ engagement in the training.
Discussion
The results suggest the ACT can be delivered to VP infants. However, challenges remain in recruitment of numerous and diverse samples. We discuss strategies to overcome these challenges informed by results of this study.
Trial registration
Registered Registration ID: NCT03896490. Retrospectively registered at Clinical Trials Protocol Registration and Results System (clinicaltrials.gov)
X-point collapse and saturation in the nonlinear tearing mode reconnection
We study the nonlinear evolution of the resistive tearing mode in slab
geometry in two dimensions. We show that, in the strongly driven regime (large
Delta'), a collapse of the X-point occurs once the island width exceeds a
certain critical value ~1/Delta'. A current sheet is formed and the
reconnection is exponential in time with a growth rate ~eta^1/2, where eta is
the resistivity. If the aspect ratio of the current sheet is sufficiently
large, the sheet can itself become tearing-mode unstable, giving rise to
secondary islands, which then coalesce with the original island. The saturated
state depends on the value of Delta'. For small Delta', the saturation
amplitude is ~Delta' and quantitatively agrees with the theoretical prediction.
If Delta' is large enough for the X-point collapse to have occured, the
saturation amplitude increases noticeably and becomes independent of Delta'.Comment: revtex4, 4 pages, 18 figure
Formation of Plasmoid Chains in Magnetic Reconnection
A detailed numerical study of magnetic reconnection in resistive MHD for very
large, previously inaccessible, Lundquist numbers () is
reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be
unstable to super-Alfv\'enically fast formation of plasmoid (magnetic-island)
chains. The plasmoid number scales as and the instability growth rate
in the linear stage as , in agreement with the theory by Loureiro et
al. [Phys. Plasmas {\bf 14}, 100703 (2007)]. In the nonlinear regime, plasmoids
continue to grow faster than they are ejected and completely disrupt the
reconnection layer. These results suggest that high-Lundquist-number
reconnection is inherently time-dependent and hence call for a substantial
revision of the standard Sweet-Parker quasi-stationary picture for .Comment: submitted to Phys. Rev. Let
Suppression of Tumor Necrosis Factor Production by Alcohol in Lipopolysaccharide-Stimulated Culture
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66388/1/j.1530-0277.1994.tb00917.x.pd
Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?
It is known that there must be some weak form of transport (called cool
bottom processing, or CBP) acting in low mass RGB and AGB stars, adding nuclei,
newly produced near the hydrogen-burning shell, to the convective envelope. We
assume that this extra-mixing originates in a stellar dynamo operated by the
differential rotation below the envelope, maintaining toroidal magnetic fields
near the hydrogen-burning shell. We use a phenomenological approach to the
buoyancy of magnetic flux tubes, assuming that they induce matter circulation
as needed by CBP models. This establishes requirements on the fields necessary
to transport material from zones where some nuclear burning takes place,
through the radiative layer, and into the convective envelope. Magnetic field
strengths are determined by the transport rates needed by CBP for the model
stellar structure of a star of initially 1.5 solar mass, in both the AGB and
RGB phases. The field required for the AGB star in the processing zone is B_0 ~
5x10^6 G; at the base of the convective envelope this yields an intensity B_E <
10^4 G (approximately). For the RGB case, B_0 ~ 5x10^4 to 4x10^5 G, and the
corresponding B_E are ~ 450 to 3500 G. These results are consistent with
existing observations on AGB stars. They also hint at the basis for high field
sources in some planetary nebulae and the very large fields found in some white
dwarfs. It is concluded that transport by magnetic buoyancy should be
considered as a possible mechanism for extra mixing through the radiative zone,
as is required by both stellar observations and the extensive isotopic data on
circumstellar condensates found in meteorites.Comment: 26 pages, 4 figures, accepted by Astrophysical Journa
Turbulent Magnetic Reconnection in Two Dimensions
Two-dimensional numerical simulations of the effect of background turbulence
on 2D resistive magnetic reconnection are presented. For sufficiently small
values of the resistivity () and moderate values of the turbulent power
(), the reconnection rate is found to have a much weaker dependence
on than the Sweet-Parker scaling of and is even consistent
with an independent value. For a given value of , the dependence
of the reconnection rate on the turbulent power exhibits a critical threshold
in above which the reconnection rate is significantly enhanced.Comment: Accepted to MNRA
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