622 research outputs found
Particle Acceleration and Magnetic Dissipation in Relativistic Current Sheet of Pair Plasmas
We study linear and nonlinear development of relativistic and
ultrarelativistic current sheets of pair plasmas with antiparallel magnetic
fields. Two types of two-dimensional problems are investigated by
particle-in-cell simulations. First, we present the development of relativistic
magnetic reconnection, whose outflow speed is an order of the light speed c. It
is demonstrated that particles are strongly accelerated in and around the
reconnection region, and that most of magnetic energy is converted into
"nonthermal" part of plasma kinetic energy. Second, we present another
two-dimensional problem of a current sheet in a cross-field plane. In this
case, the relativistic drift kink instability (RDKI) occurs. Particle
acceleration also takes place, but the RDKI fast dissipates the magnetic energy
into plasma heat. We discuss the mechanism of particle acceleration and the
theory of the RDKI in detail. It is important that properties of these two
processes are similar in the relativistic regime of T > mc^2, as long as we
consider the kinetics. Comparison of the two processes indicates that magnetic
dissipation by the RDKI is more favorable process in the relativistic current
sheet. Therefore the striped pulsar wind scenario should be reconsidered by the
RDKI.Comment: To appear in ApJ vol. 670; 60 pages, 27 figures; References and typos
are fixe
Proton acceleration in analytic reconnecting current sheets
Particle acceleration provides an important signature for the magnetic collapse that accompanies a solar flare. Most particle acceleration studies, however, invoke magnetic and electric field models that are analytically convenient rather than solutions of the governing magnetohydrodynamic equations. In this paper a self-consistent magnetic reconnection solution is employed to investigate proton orbits, energy gains, and acceleration timescales for proton acceleration in solar flares. The magnetic field configuration is derived from the analytic reconnection solution of Craig and Henton. For the physically realistic case in which magnetic pressure of the current sheet is limited at small resistivities, the model contains a single free parameter that specifies the shear of the velocity field. It is shown that in the absence of losses, the field produces particle acceleration spectra characteristic of magnetic X-points. Specifically, the energy distribution approximates a power law ~ξ-3/2 nonrelativistically, but steepens slightly at the higher energies. Using realistic values of the “effective” resistivity, we obtain energies and acceleration times that fall within the range of observational data for proton acceleration in the solar corona
Accelerated and interpretable oblique random survival forests
The oblique random survival forest (RSF) is an ensemble supervised learning
method for right-censored outcomes. Trees in the oblique RSF are grown using
linear combinations of predictors to create branches, whereas in the standard
RSF, a single predictor is used. Oblique RSF ensembles often have higher
prediction accuracy than standard RSF ensembles. However, assessing all
possible linear combinations of predictors induces significant computational
overhead that limits applications to large-scale data sets. In addition, few
methods have been developed for interpretation of oblique RSF ensembles, and
they remain more difficult to interpret compared to their axis-based
counterparts. We introduce a method to increase computational efficiency of the
oblique RSF and a method to estimate importance of individual predictor
variables with the oblique RSF. Our strategy to reduce computational overhead
makes use of Newton-Raphson scoring, a classical optimization technique that we
apply to the Cox partial likelihood function within each non-leaf node of
decision trees. We estimate the importance of individual predictors for the
oblique RSF by negating each coefficient used for the given predictor in linear
combinations, and then computing the reduction in out-of-bag accuracy. In
general benchmarking experiments, we find that our implementation of the
oblique RSF is approximately 450 times faster with equivalent discrimination
and superior Brier score compared to existing software for oblique RSFs. We
find in simulation studies that 'negation importance' discriminates between
relevant and irrelevant predictors more reliably than permutation importance,
Shapley additive explanations, and a previously introduced technique to measure
variable importance with oblique RSFs based on analysis of variance. Methods
introduced in the current study are available in the aorsf R package.Comment: 40 pages, 6 figure
Entire functions with Julia sets of positive measure
Let f be a transcendental entire function for which the set of critical and
asymptotic values is bounded. The Denjoy-Carleman-Ahlfors theorem implies that
if the set of all z for which |f(z)|>R has N components for some R>0, then the
order of f is at least N/2. More precisely, we have log log M(r,f) > (N/2) log
r - O(1), where M(r,f) denotes the maximum modulus of f. We show that if f does
not grow much faster than this, then the escaping set and the Julia set of f
have positive Lebesgue measure. However, as soon as the order of f exceeds N/2,
this need not be true. The proof requires a sharpened form of an estimate of
Tsuji related to the Denjoy-Carleman-Ahlfors theorem.Comment: 17 page
Publisher Correction: Deep learning enables fast and dense single-molecule localization with high accuracy
In the version of this Article initially published, Jacob H. Macke and Jonas Ries were not listed as corresponding authors. Their contact information and designation as corresponding authors are now included. The error has been corrected in the online version of the Article
A Summary of the Endocrine Society Clinical Practice Guidelines on Congenital Adrenal Hyperplasia due to Steroid 21-Hydroxylase Deficiency
Steroid 21-hydroxylase deficiency accounts for about 95% of cases of congenital adrenal hyperplasia (CAH). Newborns are currently being screened for the classical forms of this disease throughout the United States and in 12 other countries. As such, it seems important to develop the best practice guidelines for treating not only infants and children, but affected adults as well. This report gives a brief overview of the most recent expert opinion and clinical practice guidelines for CAH as formulated by The Endocrine Society Task Force
UV-induced ligand exchange in MHC class I protein crystals
High-throughput structure determination of protein−ligand complexes is central in drug development and structural proteomics. To facilitate such high-throughput structure determination we designed an induced replacement strategy. Crystals of a protein complex bound to a photosensitive ligand are exposed to UV light, inducing the departure of the bound ligand, allowing a new ligand to soak in. We exemplify the approach for a class of protein complexes that is especially recalcitrant to high-throughput strategies: the MHC class I proteins. We developed a UV-sensitive, “conditional”, peptide ligand whose UV-induced cleavage in the crystals leads to the exchange of the low-affinity lytic fragments for full-length peptides introduced in the crystallant solution. This “in crystallo” exchange is monitored by the loss of seleno-methionine anomalous diffraction signal of the conditional peptide compared to the signal of labeled MHC β2m subunit. This method has the potential to facilitate high-throughput crystallography in various protein families
Policy Entrepreneurship and Multilevel Governance: A Comparative Study of European Cross-Border Regions
This article was publsihed in the journal, Environment and Planning C [© Pion]. The definitive version is available at: http://www.envplan.com/C.htmlThis article addresses the recent proliferation of Cross-Border Regions, or Euroregions,
in Europe. It argues that EU multi-level governance patterns generate opportunities for
entrepreneurial policy organisations to attract policy tasks and resources. This is
conceptualised as policy entrepreneurship and applied to a comparative case study
analysis of three Euroregions: EUREGIO (Germany – Netherlands), Viadrina (Poland –
Germany) and Tyrol (Austria – Italy). The analysis focuses on the ability of these
initiatives to establish themselves as autonomous organisations. It finds considerable
variation across the cases in this respect. Following on from this, the paper shows how
different administrative and institutional environments in different EU member states
affect the ability of Euroregions to engage in policy entrepreneurship. It concludes that
is it premature to perceive Euroregions as new types of regional territorial entities;
rather, they are part of the policy innovation scenario enabled by EU multi-level
governance
Magnetoluminescence
Pulsar Wind Nebulae, Blazars, Gamma Ray Bursts and Magnetars all contain
regions where the electromagnetic energy density greatly exceeds the plasma
energy density. These sources exhibit dramatic flaring activity where the
electromagnetic energy distributed over large volumes, appears to be converted
efficiently into high energy particles and gamma-rays. We call this general
process magnetoluminescence. Global requirements on the underlying, extreme
particle acceleration processes are described and the likely importance of
relativistic beaming in enhancing the observed radiation from a flare is
emphasized. Recent research on fluid descriptions of unstable electromagnetic
configurations are summarized and progress on the associated kinetic
simulations that are needed to account for the acceleration and radiation is
discussed. Future observational, simulation and experimental opportunities are
briefly summarized.Comment: To appear in "Jets and Winds in Pulsar Wind Nebulae, Gamma-ray Bursts
and Blazars: Physics of Extreme Energy Release" of the Space Science Reviews
serie
Comparisons of electron fluxes measured in the crustal fields at Mars by the MGS magnetometer/electron reflectometer instrument with a B field–dependent transport code
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95296/1/jgre1782.pd
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