5,198 research outputs found
On the fine structure of the quiet solar \Ca II K atmosphere
We investigate the morphological, dynamical, and evolutionary properties of
the internetwork and network fine structure of the quiet sun at disk centre.
The analysis is based on a 6 h time sequence of narrow-band filtergrams
centred on the inner-wing \Ca II K reversal at 393.3 nm. The results
for the internetwork are related to predictions derived from numerical
simulations of the quiet sun. The average evolutionary time scale of the
internetwork in our observations is 52 sec. Internetwork grains show a tendency
to appear on a mesh-like pattern with a mean cell size of 4-5 arcsec.
Based on this size and the spatial organisation of the mesh we speculate that
this pattern is related to the existence of photospheric downdrafts as
predicted by convection simulations. The image segmentation shows that typical
sizes of both network and internetwork grains are in the order of 1.6 arcs.Comment: 8 pages, 9 figure
Motion clouds: model-based stimulus synthesis of natural-like random textures for the study of motion perception
Choosing an appropriate set of stimuli is essential to characterize the
response of a sensory system to a particular functional dimension, such as the
eye movement following the motion of a visual scene. Here, we describe a
framework to generate random texture movies with controlled information
content, i.e., Motion Clouds. These stimuli are defined using a generative
model that is based on controlled experimental parametrization. We show that
Motion Clouds correspond to dense mixing of localized moving gratings with
random positions. Their global envelope is similar to natural-like stimulation
with an approximate full-field translation corresponding to a retinal slip. We
describe the construction of these stimuli mathematically and propose an
open-source Python-based implementation. Examples of the use of this framework
are shown. We also propose extensions to other modalities such as color vision,
touch, and audition
Segmental Spatiotemporal CNNs for Fine-grained Action Segmentation
Joint segmentation and classification of fine-grained actions is important
for applications of human-robot interaction, video surveillance, and human
skill evaluation. However, despite substantial recent progress in large-scale
action classification, the performance of state-of-the-art fine-grained action
recognition approaches remains low. We propose a model for action segmentation
which combines low-level spatiotemporal features with a high-level segmental
classifier. Our spatiotemporal CNN is comprised of a spatial component that
uses convolutional filters to capture information about objects and their
relationships, and a temporal component that uses large 1D convolutional
filters to capture information about how object relationships change across
time. These features are used in tandem with a semi-Markov model that models
transitions from one action to another. We introduce an efficient constrained
segmental inference algorithm for this model that is orders of magnitude faster
than the current approach. We highlight the effectiveness of our Segmental
Spatiotemporal CNN on cooking and surgical action datasets for which we observe
substantially improved performance relative to recent baseline methods.Comment: Updated from the ECCV 2016 version. We fixed an important
mathematical error and made the section on segmental inference cleare
Tracing the Peculiar Dark Matter Structure in the Galaxy Cluster CL 0024+17 with Intracluster Stars and Gas
ICL is believed to originate from the stars stripped from cluster galaxies.
They are no longer gravitationally bound to individual galaxies, but to the
cluster, and their smooth distribution potentially makes them serve as much
denser tracers of the cluster dark matter than the sparsely distributed cluster
galaxies. We present our study of the ICL in Cl 0024+17 using both ACS and
Subaru data, where we previously reported discovery of a ringlike dark matter
structure with gravitational lensing. The ACS images provide much lower sky
levels than ground data, and enable us to measure relative variation of surface
brightness reliably. This analysis is repeated with the Subaru images to
examine if consistent features are recovered despite different reduction scheme
and instrumental characteristics. We find that the ICL profile clearly
resembles the peculiar mass profile, which stops decreasing at r~50" (~265 kpc)
and slowly increases until it turns over at r~75" (~397 kpc). This feature is
seen in both ACS and Subaru images for nearly all available passband images
while the features are stronger in red filters. The consistency across
different filters and instruments strongly rules out the possibility that the
feature might come from any residual, uncorrected calibration errors. In
addition, our re-analysis of the cluster X-ray data shows that the peculiar
mass structure is also indicated by a non-negligible bump in the intracluster
gas profile when the geometric center of the dark matter ring, not the peak of
the X-ray emission, is chosen as the center of the radial bin. The location of
the gas ring is closer to the center by ~15" (~80 kpc), raising an interesting
possibility that the ring-like structure is expanding and the gas ring is
lagging behind perhaps because of the ram pressure if both features in mass and
gas share the same dynamical origin.Comment: Accepted to ApJ for publicatio
Laminar Cortical Dynamics of Visual Form and Motion Interactions During Coherent Object Motion Perception
How do visual form and motion processes cooperate to compute object motion when each process separately is insufficient? A 3D FORMOTION model specifies how 3D boundary representations, which separate figures from backgrounds within cortical area V2, capture motion signals at the appropriate depths in MT; how motion signals in MT disambiguate boundaries in V2 via MT-to-Vl-to-V2 feedback; how sparse feature tracking signals are amplified; and how a spatially anisotropic motion grouping process propagates across perceptual space via MT-MST feedback to integrate feature-tracking and ambiguous motion signals to determine a global object motion percept. Simulated data include: the degree of motion coherence of rotating shapes observed through apertures, the coherent vs. element motion percepts separated in depth during the chopsticks illusion, and the rigid vs. non-rigid appearance of rotating ellipses.Air Force Office of Scientific Research (F49620-01-1-0397); National Geospatial-Intelligence Agency (NMA201-01-1-2016); National Science Foundation (BCS-02-35398, SBE-0354378); Office of Naval Research (N00014-95-1-0409, N00014-01-1-0624
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