13,625 research outputs found
A high speed Tri-Vision system for automotive applications
Purpose: Cameras are excellent ways of non-invasively monitoring the interior and exterior of vehicles. In particular, high speed stereovision and multivision systems are important for transport applications such as driver eye tracking or collision avoidance. This paper addresses the synchronisation problem which arises when multivision camera systems are used to capture the high speed motion common in such applications.
Methods: An experimental, high-speed tri-vision camera system intended for real-time driver eye-blink and saccade measurement was designed, developed, implemented and tested using prototype, ultra-high dynamic range, automotive-grade image sensors specifically developed by E2V (formerly Atmel) Grenoble SA as part of the European FP6 project – sensation (advanced sensor development for attention stress, vigilance and sleep/wakefulness monitoring).
Results : The developed system can sustain frame rates of 59.8 Hz at the full stereovision resolution of 1280 × 480 but this can reach 750 Hz when a 10 k pixel Region of Interest (ROI) is used, with a maximum global shutter speed of 1/48000 s and a shutter efficiency of 99.7%. The data can be reliably transmitted uncompressed over standard copper Camera-Link® cables over 5 metres. The synchronisation error between the left and right stereo images is less than 100 ps and this has been verified both electrically and optically. Synchronisation is automatically established at boot-up and maintained during resolution changes. A third camera in the set can be configured independently. The dynamic range of the 10bit sensors exceeds 123 dB with a spectral sensitivity extending well into the infra-red range.
Conclusion: The system was subjected to a comprehensive testing protocol, which confirms that the salient requirements for the driver monitoring application are adequately met and in some respects, exceeded. The synchronisation technique presented may also benefit several other automotive stereovision applications including near and far-field obstacle detection and collision avoidance, road condition monitoring and others.Partially funded by the EU FP6 through the IST-507231 SENSATION project.peer-reviewe
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
Random bits, true and unbiased, from atmospheric turbulence
Random numbers represent a fundamental ingredient for numerical simulation,
games, informa- tion science and secure communication. Algorithmic and
deterministic generators are affected by insufficient information entropy. On
the other hand, suitable physical processes manifest intrinsic unpredictability
that may be exploited for generating genuine random numbers with an entropy
reaching the ideal limit. In this work, we present a method to extract genuine
random bits by using the atmospheric turbulence: by sending a laser beam along
a 143Km free-space link, we took advantage of the chaotic behavior of air
refractive index in the optical propagation. Random numbers are then obtained
by converting in digital units the aberrations and distortions of the received
laser wave-front. The generated numbers, obtained without any post-processing,
pass the most selective randomness tests. The core of our extracting algorithm
can be easily generalized for other physical processes
Dynamical Constraints on The Masses of the Nuclear Star Cluster and Black Hole in the Late-Type Spiral Galaxy NGC 3621
NGC 3621 is a late-type (Sd) spiral galaxy with an active nucleus, previously
detected through mid-infrared [Ne V] line emission. Archival Hubble Space
Telescope (HST) images reveal that the galaxy contains a bright and compact
nuclear star cluster. We present a new high-resolution optical spectrum of this
nuclear cluster, obtained with the ESI Spectrograph at the Keck Observatory.
The nucleus has a Seyfert 2 emission-line spectrum at optical wavelengths,
supporting the hypothesis that a black hole is present. The line-of-sight
stellar velocity dispersion of the cluster is sigma=43+/-3 km/s, one of the
largest dispersions measured for any nuclear cluster in a late-type spiral
galaxy. Combining this measurement with structural parameters measured from
archival HST images, we carry out dynamical modeling based on the Jeans
equation for a spherical star cluster containing a central point mass. The
maximum black hole mass consistent with the measured stellar velocity
dispersion is 3*10^6 solar masses. If the black hole mass is small compared
with the cluster's stellar mass, then the dynamical models imply a total
stellar mass of ~1*10^7 solar masses, which is consistent with rough estimates
of the stellar mass based on photometric measurements from HST images. From
structural decomposition of 2MASS images, we find no clear evidence for a bulge
in NGC 3621; the galaxy contains at most a very faint and inconspicuous
pseudobulge component (M_K>-17.6 mag). NGC 3621 provides one of the best
demonstrations that very late-type spirals can host both active nuclei and
nuclear star clusters, and that low-mass black holes can occur in disk galaxies
even in the absence of a substantial bulge.Comment: 13 pages, 10 figures. Accepted for publication in Ap
3D Spectrophotometry of Planetary Nebulae in the Bulge of M31
We introduce crowded field integral field (3D) spectrophotometry as a useful
technique for the study of resolved stellar populations in nearby galaxies. As
a methodological test, we present a pilot study with selected extragalactic
planetary nebulae (XPN) in the bulge of M31, demonstrating how 3D spectroscopy
is able to improve the limited accuracy of background subtraction which one
would normally obtain with classical slit spectroscopy. It is shown that due to
the absence of slit effects, 3D is a most suitable technique for
spectrophometry. We present spectra and line intensities for 5 XPN in M31,
obtained with the MPFS instrument at the Russian 6m BTA, INTEGRAL at the WHT,
and with PMAS at the Calar Alto 3.5m Telescope. Using 3D spectra of bright
standard stars, we demonstrate that the PSF is sampled with high accuracy,
providing a centroiding precision at the milli-arcsec level. Crowded field 3D
spectrophotometry and the use of PSF fitting techniques is suggested as the
method of choice for a number of similar observational problems, including
luminous stars in nearby galaxies, supernovae, QSO host galaxies,
gravitationally lensed QSOs, and others.Comment: (1) Astrophysikalisches Institut Potsdam, (2) University of Durham.
18 pages, 11 figures, accepted for publication in Ap
Evaporating pure, binary and ternary droplets: thermal effects and axial symmetry breaking
The Greek aperitif Ouzo is not only famous for its specific anise-flavored
taste, but also for its ability to turn from a transparent miscible liquid to a
milky-white colored emulsion when water is added. Recently, it has been shown
that this so-called Ouzo effect, i.e. the spontaneous emulsification of oil
microdroplets, can also be triggered by the preferential evaporation of ethanol
in an evaporating sessile Ouzo drop, leading to an amazingly rich drying
process with multiple phase transitions [H. Tan et al., Proc. Natl. Acad. Sci.
USA 113(31) (2016) 8642]. Due to the enhanced evaporation near the contact
line, the nucleation of oil droplets starts at the rim which results in an oil
ring encircling the drop. Furthermore, the oil droplets are advected through
the Ouzo drop by a fast solutal Marangoni flow. In this article, we investigate
the evaporation of mixture droplets in more detail, by successively increasing
the mixture complexity from pure water over a binary water-ethanol mixture to
the ternary Ouzo mixture (water, ethanol and anise oil). In particular,
axisymmetric and full three-dimensional finite element method simulations have
been performed on these droplets to discuss thermal effects and the complicated
flow in the droplet driven by an interplay of preferential evaporation,
evaporative cooling and solutal and thermal Marangoni flow. By using image
analysis techniques and micro-PIV measurements, we are able to compare the
numerically predicted volume evolutions and velocity fields with experimental
data. The Ouzo droplet is furthermore investigated by confocal microscopy. It
is shown that the oil ring predominantly emerges due to coalescence
Acetylcholine Receptors and Concanavalin A-Binding Sites on Cultured Xenopus Muscle Cells: Electrophoresis, Diffusion, and Aggregation
Using digitally analyzed fluorescence videomicroscopy, we have examined the behavior of acetylcholine receptors and concanavalin A binding sites in response to externally applied electric fields. The distributions of these molecules on cultured Xenopus myoballs were used to test a simple model which assumes that electrophoresis and diffusion are the only important processes involved. The model describes the distribution of concanavalin A sites quite well over a fourfold range of electric field strengths; the results suggest an average diffusion constant of ~2.3 X 10^(-9) cm^2/s. At higher electric field strengths, the asymmetry seen is substantially less than that predicted by the model. Acetylcholine receptors subjected to electric fields show distributions substantially different from those predicted on the basis of simple electrophoresis and diffusion, and evidence a marked tendency to aggregate. Our results suggest that this aggregation is due to lateral migration of surface acetylcholine receptors, and is dependent on surface interactions, rather than the rearrangement of microfilaments or microtubules. The data are consistent with a diffusion-trap mechanism of receptor aggregation, and suggest that the event triggering receptor localization is a local increase in the concentration of acetylcholine receptors, or the electrophoretic concentration of some other molecular species. These observations suggest that, whatever mechanism(s) trigger initial clustering events in vivo, the accumulation of acetylcholine receptors can be substantially enhanced by passive, diffusion-mediated aggregation
Investigation of bottom fishing impacts on benthic structure using multibeam sonar, sidescan and video
Bottom fishing gear is known to alter benthic structure, however changes in the shape of the sea floor are often too subtle to be detected by acoustic remote sensing. Nonetheless, long linear features were observed during a recent high-resolution multibeam sonar survey of Jeffreys Ledge, a prominent fishing ground in Gulf of Maine, located about 50 km from Portsmouth, NH. These marks, which have a relief of only few centimeters, are presumed to be caused by bottom dredging gear used in the area for scallop and clam fisheries. The extraction of these small features from a noisy data set (including several instrumental artifacts) presented a number of challenges. To enhance the detection and identification of these features, data artifacts were identified and removed selectively using frequency filtering. Verification was attempted with sidescan sonar and video surveys. While clearly visible on the sidescan sonar records, the bottom marks were not discernable in the video survey. The inability to see the bottom marks with video may be related to the age of the marks, and has important ramifications about appropriate methodologies for quantifying gear impact. Results from multibeam sonar, sidescan sonar and video surveys suggest that the best methodology to deal with inspection of bottom fishing marks is to integrate data in a 3D GIS-like environment
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