28,532 research outputs found
Event-based Vision: A Survey
Event cameras are bio-inspired sensors that differ from conventional frame
cameras: Instead of capturing images at a fixed rate, they asynchronously
measure per-pixel brightness changes, and output a stream of events that encode
the time, location and sign of the brightness changes. Event cameras offer
attractive properties compared to traditional cameras: high temporal resolution
(in the order of microseconds), very high dynamic range (140 dB vs. 60 dB), low
power consumption, and high pixel bandwidth (on the order of kHz) resulting in
reduced motion blur. Hence, event cameras have a large potential for robotics
and computer vision in challenging scenarios for traditional cameras, such as
low-latency, high speed, and high dynamic range. However, novel methods are
required to process the unconventional output of these sensors in order to
unlock their potential. This paper provides a comprehensive overview of the
emerging field of event-based vision, with a focus on the applications and the
algorithms developed to unlock the outstanding properties of event cameras. We
present event cameras from their working principle, the actual sensors that are
available and the tasks that they have been used for, from low-level vision
(feature detection and tracking, optic flow, etc.) to high-level vision
(reconstruction, segmentation, recognition). We also discuss the techniques
developed to process events, including learning-based techniques, as well as
specialized processors for these novel sensors, such as spiking neural
networks. Additionally, we highlight the challenges that remain to be tackled
and the opportunities that lie ahead in the search for a more efficient,
bio-inspired way for machines to perceive and interact with the world
Glacial cycles drive variations in the production of oceanic crust
Glacial cycles redistribute water between oceans and continents causing
pressure changes in the upper mantle, with consequences for melting of Earth's
interior. Using Plio-Pleistocene sea-level variations as a forcing function,
theoretical models of mid-ocean ridge dynamics that include melt transport
predict temporal variations in crustal thickness of hundreds of meters. New
bathymetry from the Australian-Antarctic ridge shows significant spectral
energy near the Milankovitch periods of 23, 41, and 100 ky, consistent with
model predictions. These results suggest that abyssal hills, one of the most
common bathymetric features on Earth, record the magmatic response to changes
in sea level. The models and data support a link between glacial cycles at the
surface and mantle melting at depth, recorded in the bathymetric fabric of the
sea floor.Comment: 30 pages, 6 figures (including supplementary information).
Resubmitted to Science on 12 December 201
A Case Study of Low-Mass Star Formation
This article synthesizes observational data from an extensive program aimed
toward a comprehensive understanding of star formation in a low-mass
star-forming molecular cloud. New observations and published data spanning from
the centimeter wave band to the near infrared reveal the high and low density
molecular gas, dust, and pre-main sequence stars in L1551.Comment: 24 pages, 21 figures, ApJS accepte
Continuous measurements of discharge from a horizontal acoustic Doppler current profiler in a tidal river
Acoustic Doppler current profilers (ADCPs) can be mounted horizontally at a river bank, yielding single-depth horizontal array observations of velocity across the river. This paper presents a semideterministic, semistochastic method to obtain continuous measurements of discharge from horizontal ADCP (HADCP) data in a tidal river. In the deterministic part, single-depth velocity data are converted to specific discharge by applying the law of the wall, which requires knowledge of local values of the bed roughness length (z0). A new filtration technique was developed to infer cross-river profiles of z0 from moving boat ADCP measurements. Width-averaged values of z0 were shown to be predominantly constant in time but differed between ebb and flood. In the stochastic part of the method, specific discharge was converted to total discharge on the basis of a model that accounts for the time lag between flow variation in the central part of the river and flow variation near the banks. Model coefficients were derived using moving boat ADCP data. The consistency of mutually independent discharge estimates from HADCP measurements was investigated to validate the method, analyzing river discharge and tidal discharge separately. Inaccuracy of the method is attributed primarily to mechanisms controlling transverse exchange of momentum, which produce temporal variation in the discharge distribution over the cross section. Specifically, development of river dunes may influence the portion of the discharge concentrated within the range of the HADC
An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
The mass of a protoplanetary disk limits the formation and future growth of
any planet. Masses of protoplanetary disks are usually calculated from
measurements of the dust continuum emission by assuming an interstellar
gas-to-dust ratio. To investigate the utility of CO as an alternate probe of
disk mass, we use ALMA to survey CO and CO J = line
emission from a sample of 93 protoplanetary disks around stars and brown dwarfs
with masses from 0.03 -- 2 M in the nearby Chamaeleon I star-forming
region. We detect CO emission from 17 sources and CO from only
one source. Gas masses for disks are then estimated by comparing the CO line
luminosities to results from published disk models that include CO freeze-out
and isotope-selective photodissociation. Under the assumption of a typical ISM
CO-to-H ratios of , the resulting gas masses are implausibly low,
with an average gas mass of 0.05 M as inferred from the average
flux of stacked CO lines. The low gas masses and gas-to-dust ratios for
Cha I disks are both consistent with similar results from disks in the Lupus
star-forming region. The faint CO line emission may instead be explained if
disks have much higher gas masses, but freeze-out of CO or complex C-bearing
molecules is underestimated in disk models. The conversion of CO flux to CO gas
mass also suffers from uncertainties in disk structures, which could affect gas
temperatures. CO emission lines will only be a good tracer of the disk mass
when models for C and CO depletion are confirmed to be accurate.Comment: accepted for publication in Ap
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