10,146 research outputs found
An Algorithm for constructing Hjelmslev planes
Projective Hjelmslev planes and Affine Hjelmselv planes are generalisations
of projective planes and affine planes. We present an algorithm for
constructing a projective Hjelmslev planes and affine Hjelsmelv planes using
projective planes, affine planes and orthogonal arrays. We show that all
2-uniform projective Hjelmslev planes, and all 2-uniform affine Hjelsmelv
planes can be constructed in this way. As a corollary it is shown that all
2-uniform Affine Hjelmselv planes are sub-geometries of 2-uniform projective
Hjelmselv planes.Comment: 15 pages. Algebraic Design Theory and Hadamard matrices, 2014,
Springer Proceedings in Mathematics & Statistics 13
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
QED calculation of the n=1 and n=2 energy levels in He-like ions
We perform ab initio QED calculations of energy levels for the and
states of He-like ions with the nuclear charge in the range -100.
The complete set of two-electron QED corrections is evaluated to all orders in
the parameter \aZ. Uncalculated contributions to energy levels come through
orders \alpha^3 (\aZ)^2, \alpha^2 (\aZ)^7, and higher. The calculation
presented is the first treatment for excited states of He-like ions complete
through order \alpha^2 (\aZ)^4. A significant improvement in accuracy of
theoretical predictions is achieved, especially in the high- region.Comment: 23 pages, 5 figure
Some Pattern Recognition Challenges in Data-Intensive Astronomy
We review some of the recent developments and challenges posed by the data
analysis in modern digital sky surveys, which are representative of the
information-rich astronomy in the context of Virtual Observatory. Illustrative
examples include the problems of an automated star-galaxy classification in
complex and heterogeneous panoramic imaging data sets, and an automated,
iterative, dynamical classification of transient events detected in synoptic
sky surveys. These problems offer good opportunities for productive
collaborations between astronomers and applied computer scientists and
statisticians, and are representative of the kind of challenges now present in
all data-intensive fields. We discuss briefly some emergent types of scalable
scientific data analysis systems with a broad applicability.Comment: 8 pages, compressed pdf file, figures downgraded in quality in order
to match the arXiv size limi
The Effects of Turbulence on Three-Dimensional Magnetic Reconnection at the Magnetopause
Two- and three-dimensional particle-in-cell simulations of a recent encounter
of the Magnetospheric Multiscale Mission (MMS) with an electron diffusion
region at the magnetopause are presented. While the two-dimensional simulation
is laminar, turbulence develops at both the x-line and along the magnetic
separatrices in the three-dimensional simulation. The turbulence is strong
enough to make the magnetic field around the reconnection island chaotic and
produces both anomalous resistivity and anomalous viscosity. Each contribute
significantly to breaking the frozen-in condition in the electron diffusion
region. A surprise is that the crescent-shaped features in velocity space seen
both in MMS observations and in two-dimensional simulations survive, even in
the turbulent environment of the three-dimensional system. This suggests that
MMS's measurements of crescent distributions do not exclude the possibility
that turbulence plays an important role in magnetopause reconnection.Comment: Revised version accepted by GR
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