28,253 research outputs found
Multispectral fingerprinting for improved in vivo cell dynamics analysis
Background:
Tracing cell dynamics in the embryo becomes tremendously difficult when cell trajectories cross in space and time and tissue density obscure individual cell borders. Here, we used the chick neural crest (NC) as a model to test multicolor cell labeling and multispectral confocal imaging strategies to overcome these roadblocks.
Results:
We found that multicolor nuclear cell labeling and multispectral imaging led to improved resolution of in vivo NC cell identification by providing a unique spectral identity for each cell. NC cell spectral identity allowed for more accurate cell tracking and was consistent during short term time-lapse imaging sessions. Computer model simulations predicted significantly better object counting for increasing cell densities in 3-color compared to 1-color nuclear cell labeling. To better resolve cell contacts, we show that a combination of 2-color membrane and 1-color nuclear cell labeling dramatically improved the semi-automated analysis of NC cell interactions, yet preserved the ability to track cell movements. We also found channel versus lambda scanning of multicolor labeled embryos significantly reduced the time and effort of image acquisition and analysis of large 3D volume data sets.
Conclusions:
Our results reveal that multicolor cell labeling and multispectral imaging provide a cellular fingerprint that may uniquely determine a cell's position within the embryo. Together, these methods offer a spectral toolbox to resolve in vivo cell dynamics in unprecedented detail
Change detection in SAR time-series based on the coefficient of variation
This paper discusses change detection in SAR time-series. Firstly, several
statistical properties of the coefficient of variation highlight its pertinence
for change detection. Then several criteria are proposed. The coefficient of
variation is suggested to detect any kind of change.
Then other criteria based on ratios of coefficients of variations are
proposed to detect long events such as construction test sites, or point-event
such as vehicles.
These detection methods are evaluated first on theoretical statistical
simulations to determine the scenarios where they can deliver the best results.
Then detection performance is assessed on real data for different types of
scenes and sensors (Sentinel-1, UAVSAR). In particular, a quantitative
evaluation is performed with a comparison of our solutions with
state-of-the-art methods
Outflowing activity in the UCHII region G045.47+0.05
Aims. This work aims at investigating the molecular gas in the surroundings
of the ultra-compact HII region G045.47+0.05 looking for evidence of molecular
outflows. Methods. We carried out observations towards a region of 2 arcmin x 2
arcmin centered at RA=19h 14m 25.6s, dec.= 11deg 09m 27.6s (J2000) using the
Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12CO J=3-2,
13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22
arcsec. We complement these observations with public infrared data. Results. We
characterize the physical parameters of the molecular clump where G045.47+0.0
is embedded. The detection of the CS J=7-6 line emission in the region reveals
that the ultra-compact HII region G045.47+0.0 has not completely disrupted the
dense gas where it was born. The HCO+ abundance observed towards G045.47+0.0
suggests the presence of molecular outflow activity in the region. From the
analysis of the 12CO J=3-2 transition we report the presence of bipolar
molecular outflows with a total mass of about 300 solar masses . We derive a
dynamical time (flow's age) of about 10^5 yr for the outflow gas, in agreement
with the presence of an ultra-compact HII region. We identify the source 2MASS
19142564+1109283 as the massive protostar candidate to drive the molecular
outflows. Based on the analysis of its spectral energy distribution we infer
that it is an early B-type star of about 15 solar masses. The results of this
work support the scenario where the formation of massive stars, at least up to
early B-type stars, is similar to that of low mass stars.Comment: Recently accepted for publication in A&
Spitzer Observations of Interstellar Object 1I/`Oumuamua
1I/`Oumuamua is the first confirmed interstellar body in our Solar System.
Here we report on observations of `Oumuamua made with the Spitzer Space
Telescope on 2017 November 21--22 (UT). We integrated for 30.2~hours at 4.5
micron (IRAC channel 2). We did not detect the object and place an upper limit
on the flux of 0.3 uJy (3sigma). This implies an effective spherical diameter
less than [98, 140, 440] meters and albedo greater than [0.2, 0.1, 0.01] under
the assumption of low, middle, or high thermal beaming parameter eta,
respectively. With an aspect ratio for `Oumuamua of 6:1, these results
correspond to dimensions of [240:40, 341:57, 1080:180] meters, respectively. We
place upper limits on the amount of dust, CO, and CO2 coming from this object
that are lower than previous results; we are unable to constrain the production
of other gas species. Both our size and outgassing limits are important because
`Oumuamua's trajectory shows non-gravitational accelerations that are sensitive
to size and mass and presumably caused by gas emission. We suggest that
`Oumuamua may have experienced low-level post-perihelion volatile emission that
produced a fresh, bright, icy mantle. This model is consistent with the
expected eta value and implied high albedo value for this solution, but, given
our strict limits on CO and CO2, requires another gas species --- probably H2O
--- to explain the observed non-gravitational acceleration. Our results extend
the mystery of `Oumuamua's origin and evolution
- …