20,332 research outputs found
Initial steps towards automatic segmentation of the wire frame of stent grafts in CT data
For the purpose of obtaining a geometrical model of the wire frame of stent grafts, we propose three tracking methods to segment the stent's wire, and compare them in an experiment. A 2D test image was created by obtaining a projection of a 3D volume containing a stent. The image was modified to connect the parts of the stent's frame and thus create a single path. Ten versions of this image were obtained by adding different noise realizations. Each algorithm was started at the start of each of the ten images, after which the traveled paths were compared to the known correct path to determine the performance. Additionally, the algorithms were applied to 3D clinical data and visually inspected. The method based on the minimum cost path algorithm scored excellent in the experiment and showed good results on the 3D data. Future research will focus on establishing a geometrical model by determining the corner points and the crossings from the results of this method.\u
Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons
We report on the physical properties of solar sequential chromospheric
brightenings (SCBs) observed in conjunction with moderate-sized chromospheric
flares with associated CMEs. To characterize these ephemeral events, we
developed automated procedures to identify and track subsections (kernels) of
solar flares and associated SCBs using high resolution H-alpha images.
Following the algorithmic identification and a statistical analysis, we compare
and find the following: SCBs are distinctly different from flare kernels in
their temporal characteristics of intensity, Doppler structure, duration, and
location properties. We demonstrate that flare ribbons are themselves made up
of subsections exhibiting differing characteristics. Flare kernels are measured
to have a mean propagation speed of 0.2 km/s and a maximum speed of 2.3 km/s
over a mean distance of 5 x 10^3 km. Within the studied population of SCBs,
different classes of characteristics are observed with coincident negative,
positive, or both negative and positive Doppler shifts of a few km/s. The
appearance of SCBs precede peak flare intensity by ~12 minutes and decay ~1
hour later. They are also found to propagate laterally away from flare center
in clusters at 41 km/s or 89 km/s. Given SCBs distinctive nature compared to
flares, we suggest a different physical mechanism relating to their origin than
the associated flare. We present a heuristic model of the origin of SCBs.Comment: 24 pages, 17 figure
Cache-aware Performance Modeling and Prediction for Dense Linear Algebra
Countless applications cast their computational core in terms of dense linear
algebra operations. These operations can usually be implemented by combining
the routines offered by standard linear algebra libraries such as BLAS and
LAPACK, and typically each operation can be obtained in many alternative ways.
Interestingly, identifying the fastest implementation -- without executing it
-- is a challenging task even for experts. An equally challenging task is that
of tuning each routine to performance-optimal configurations. Indeed, the
problem is so difficult that even the default values provided by the libraries
are often considerably suboptimal; as a solution, normally one has to resort to
executing and timing the routines, driven by some form of parameter search. In
this paper, we discuss a methodology to solve both problems: identifying the
best performing algorithm within a family of alternatives, and tuning
algorithmic parameters for maximum performance; in both cases, we do not
execute the algorithms themselves. Instead, our methodology relies on timing
and modeling the computational kernels underlying the algorithms, and on a
technique for tracking the contents of the CPU cache. In general, our
performance predictions allow us to tune dense linear algebra algorithms within
few percents from the best attainable results, thus allowing computational
scientists and code developers alike to efficiently optimize their linear
algebra routines and codes.Comment: Submitted to PMBS1
A Universal Update-pacing Framework For Visual Tracking
This paper proposes a novel framework to alleviate the model drift problem in
visual tracking, which is based on paced updates and trajectory selection.
Given a base tracker, an ensemble of trackers is generated, in which each
tracker's update behavior will be paced and then traces the target object
forward and backward to generate a pair of trajectories in an interval. Then,
we implicitly perform self-examination based on trajectory pair of each tracker
and select the most robust tracker. The proposed framework can effectively
leverage temporal context of sequential frames and avoid to learn corrupted
information. Extensive experiments on the standard benchmark suggest that the
proposed framework achieves superior performance against state-of-the-art
trackers.Comment: Submitted to ICIP 201
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