639 research outputs found
The 1.17-day orbit of the double-degenerate (DA+DQ) NLTT 16249
New spectroscopic observations show that the double degenerate system NLTT
16249 is in a close orbit (a = 5.6+/-0.3 R_sun) with a period of 1.17 d. The
total mass of the system is estimated between 1.47 and 2.04 M_sun but it is not
expected to merge within a Hubble time-scale (t_merge ~ 10^11 yr). Vennes &
Kawka (2012, ApJ, 745, L12) originally identified the system because of the
peculiar composite hydrogen (DA class) and molecular (C_2--DQ class--and CN)
spectra and the new observations establish this system as the first DA plus DQ
close double degenerate. Also, the DQ component was the first of its class to
show nitrogen dredged-up from the core in its atmosphere. The star may be
viewed as the first known DQ descendant of the born-again PG1159 stars.
Alternatively, the presence of nitrogen may be the result of past interactions
and truncated evolution in a close binary system.Comment: published in ApJ Letter
Benchmarking Image Sensors Under Adverse Weather Conditions for Autonomous Driving
Adverse weather conditions are very challenging for autonomous driving
because most of the state-of-the-art sensors stop working reliably under these
conditions. In order to develop robust sensors and algorithms, tests with
current sensors in defined weather conditions are crucial for determining the
impact of bad weather for each sensor. This work describes a testing and
evaluation methodology that helps to benchmark novel sensor technologies and
compare them to state-of-the-art sensors. As an example, gated imaging is
compared to standard imaging under foggy conditions. It is shown that gated
imaging outperforms state-of-the-art standard passive imaging due to
time-synchronized active illumination
A Benchmark for Lidar Sensors in Fog: Is Detection Breaking Down?
Autonomous driving at level five does not only means self-driving in the
sunshine. Adverse weather is especially critical because fog, rain, and snow
degrade the perception of the environment. In this work, current state of the
art light detection and ranging (lidar) sensors are tested in controlled
conditions in a fog chamber. We present current problems and disturbance
patterns for four different state of the art lidar systems. Moreover, we
investigate how tuning internal parameters can improve their performance in bad
weather situations. This is of great importance because most state of the art
detection algorithms are based on undisturbed lidar data
Fast Normal Approximation of Point Clouds in Screen Space
Displaying large point clouds of mainly planar point distributions yet comes with large restrictions regarding
the surface normal and surface reconstruction. Point data needs to be clustered or traversed to extract a local
neighborhood which is necessary to retrieve surface information. We propose using the rendering pipeline to
circumvent a pre-computation of the neighborhood in world space to perform a fast approximation of the surface
in screen space. We present and compare three different methods for surface reconstruction within a post-process.
These methods range from simple approximations to the definition of a tensor surface. All these methods are
designed to run at interactive frame-rates. We also present a correction method to increase reconstruction quality,
while preserving interactive frame-rates. Our results indicate, that the on-the-fly computation of surface normals
is not a limiting factor on modern GPUs. As the surface information is generated during the post-process, only the
target display size is the limiting factor. The performance is independent of the point cloud’s size
Using Machine Learning to Detect Ghost Images in Automotive Radar
Radar sensors are an important part of driver assistance systems and
intelligent vehicles due to their robustness against all kinds of adverse
conditions, e.g., fog, snow, rain, or even direct sunlight. This robustness is
achieved by a substantially larger wavelength compared to light-based sensors
such as cameras or lidars. As a side effect, many surfaces act like mirrors at
this wavelength, resulting in unwanted ghost detections. In this article, we
present a novel approach to detect these ghost objects by applying data-driven
machine learning algorithms. For this purpose, we use a large-scale automotive
data set with annotated ghost objects. We show that we can use a
state-of-the-art automotive radar classifier in order to detect ghost objects
alongside real objects. Furthermore, we are able to reduce the amount of false
positive detections caused by ghost images in some settings
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