3,661 research outputs found
Chromospheric dynamics
This brief review advertises a breakthrough in solar dynamics:
the identification of chromospheric Ca II K2V "grains" as manifestations
of acoustic shocks. The successful numerical reproduction of the intricate
spectral characteristics of K2V grain formation by Carlsson & Stein shows
that the non-magnetic solar chromosphere is pervaded by outward traveling
shocks to such extent that static modeling is no longer acceptable. Dynamical modeling should soon reconcile the long-standing Ca II/CO dichotomy.
The chromospheric dynamics of the magnetized regions remains enigmatic
Evaluation of Deep Convolutional Nets for Document Image Classification and Retrieval
This paper presents a new state-of-the-art for document image classification
and retrieval, using features learned by deep convolutional neural networks
(CNNs). In object and scene analysis, deep neural nets are capable of learning
a hierarchical chain of abstraction from pixel inputs to concise and
descriptive representations. The current work explores this capacity in the
realm of document analysis, and confirms that this representation strategy is
superior to a variety of popular hand-crafted alternatives. Experiments also
show that (i) features extracted from CNNs are robust to compression, (ii) CNNs
trained on non-document images transfer well to document analysis tasks, and
(iii) enforcing region-specific feature-learning is unnecessary given
sufficient training data. This work also makes available a new labelled subset
of the IIT-CDIP collection, containing 400,000 document images across 16
categories, useful for training new CNNs for document analysis
From normal brain and behavior to schzophrenia
Air Force Office of Scientific Research (F49620-01-1-0397); Office of Naval Research (N00014-01-1-0624
Chromosperic oscillations
This review concentrates on the quiet-Sun chromosphere.
Its internetwork areas are dynamically dominated by the
so-called chromospheric three-minute oscillation. They
are interpretationally dominated by the so-called Ca II
K 2V and H 2V grains. The main points of this review are
that the one phenomenon explains the other (both ways),
that the quiet-Sun chromosphere is a clapotisphere per-
vaded by shocks above h = 1 Mm, and that the existence
of the classical temperature minimum is in doubt
Explanation of the activity sensitivity of Mn I 5394.7 \AA
There is a long-standing controversy concerning the reason why the Mn I
5394.7 A line in the solar irradiance spectrum brightens more at larger
activity than most other photospheric lines. The claim that this activity
sensitivity is caused by spectral interlocking to chromospheric emission in Mg
II h & k is disputed.
Classical one-dimensional modeling is used for demonstration; modern
three-dimensional MHD simulation for verification and analysis.
The Mn I 5394.7 A line thanks its unusual sensitivity to solar activity to
its hyperfine structure. This overrides the thermal and granular Doppler
smearing through which the other, narrower, photospheric lines lose such
sensitivity. We take the nearby Fe I 5395.2 A line as example of the latter and
analyze the formation of both lines in detail to demonstrate and explain
granular Doppler brightening. We show that this affects all narrow lines.
Neither the chromosphere nor Mg II h & k play a role, nor is it correct to
describe the activity sensitivity of Mn I 5394.7 A through plage models with
outward increasing temperature contrast.
The Mn I 5394.7 A line represents a proxy diagnostic of strong-field magnetic
concentrations in the deep solar photosphere comparable to the G band and the
blue wing of H-alpha, but not a better one than these. The Mn I lines are more
promising as diagnostic of weak fields in high-resolution Stokes polarimetry.Comment: 12 pages, 8 figures, accepted by A&
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