73,983 research outputs found
Observational Test of Coronal Magnetic Field Models I. Comparison with Potential Field Model
Recent advances have made it possible to obtain two-dimensional line-of-sight
magnetic field maps of the solar corona from spectropolarimetric observations
of the Fe XIII 1075 nm forbidden coronal emission line. Together with the
linear polarization measurements that map the azimuthal direction of the
coronal magnetic field, these coronal vector magnetograms now allow for direct
observational testing of theoretical coronal magnetic field models. This paper
presents a study testing the validity of potential-field coronal magnetic field
models. We constructed a theoretical coronal magnetic field model of active
region AR 10582 observed by the SOLARC coronagraph in 2004 by a global
potential field extrapolation of the synoptic map of Carrington Rotation 2014.
Synthesized linear and circular polarization maps from thin layers of the
coronal magnetic field model above the active region along the line of sight
are compared with the observed maps. We found that reasonable agreement occurs
from layers located just above the sunspot of AR 10582, near the plane of the
sky. This result provides the first observational evidence that potential field
extrapolation can yield a reasonable approximation of the magnetic field
configuration of the solar corona for simple and stable active regions.Comment: 25 pages, 11 figures. ApJ in pres
Interactive image segmentation based on level sets of probabilities
In this paper, we present a robust and accurate algorithm for interactive image segmentation. The level set method is clearly advantageous for image objects with a complex topology and fragmented appearance. Our method integrates discriminative classification models and distance transforms with the level set method to avoid local minima and better snap to true object boundaries. The level set function approximates a transformed version of pixelwise posterior probabilities of being part of a target object. The evolution of its zero level set is driven by three force terms, region force, edge field force, and curvature force. These forces are based on a probabilistic classifier and an unsigned distance transform of salient edges. We further propose a technique that improves the performance of both the probabilistic classifier and the level set method over multiple passes. It makes the final object segmentation less sensitive to user interactions. Experiments and comparisons demonstrate the effectiveness of our method. © 2012 IEEE.published_or_final_versio
Fermions in gravity and gauge backgrounds on a brane world
We solve the fermionic zero modes in gravity and gauge backgrounds on a brane
involving a warped geometry, and study the localization of spin 1/2 fermionic
field on the brane world. The result is that there exist massless spin 1/2
fermions which can be localized on the bulk with the exponentially decreasing
warp factor if including U(1) gauge background. Two special cases of gauge
backgrounds on the extra dimensional manifold are discussed.Comment: 11 pages, no figures, final versio
Performance of Cross-layer Design with Multiple Outdated Estimates in Multiuser MIMO System
By combining adaptive modulation (AM) and automatic repeat request (ARQ) protocol as well as user scheduling, the cross-layer design scheme of multiuser MIMO system with imperfect feedback is presented, and multiple outdated estimates method is proposed to improve the system performance. Based on this method and imperfect feedback information, the closed-form expressions of spectral efficiency (SE) and packet error rate (PER) of the system subject to the target PER constraint are respectively derived. With these expressions, the system performance can be effectively evaluated. To mitigate the effect of delayed feedback, the variable thresholds (VTs) are also derived by means of the maximum a posteriori method, and these VTs include the conventional fixed thresholds (FTs) as special cases. Simulation results show that the theoretical SE and PER are in good agreement with the corresponding simulation. The proposed CLD scheme with multiple estimates can obtain higher SE than the existing CLD scheme with single estimate, especially for large delay. Moreover, the CLD scheme with VTs outperforms that with conventional FTs
Localization of fermionic fields on braneworlds with bulk tachyon matter
Recently, Pal and Skar in [arXiv:hep-th/0701266] proposed a mechanism to
arise the warped braneworld models from bulk tachyon matter, which are endowed
with a thin brane and a thick brane. In this framework, we investigate
localization of fermionic fields on these branes. As in the 1/2 spin case, the
field can be localized on both the thin and thick branes with inclusion of
scalar background. In the 3/2 spin extension, the general supergravity action
coupled to chiral supermultiplets is considered to produce the localization on
both the branes as a result.Comment: 9 pages, no figure
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