527 research outputs found
Estimation of high-resolution dust column density maps. Comparison of modified black-body fits and radiative transfer modelling
Sub-millimetre dust emission is often used to derive the column density N of
dense interstellar clouds. The observations consist of data at several
wavelengths but of variable resolution. We examine two procedures that been
proposed for the estimation of high resolution N maps. Method A uses a
low-resolution temperature map combined with higher resolution intensity data
while Method B combines N estimates from different wavelength ranges. Our aim
is to determine the accuracy of the methods relative to the true column
densities and the estimates obtainable with radiative transfer modelling. We
use magnetohydrodynamical (MHD) simulations and radiative transfer calculations
to simulate sub-millimetre observations at the wavelengths of the Herschel
Space Observatory. The observations are analysed with the methods and the
results compared to the true values and to the results from radiative transfer
modelling of observations. Both methods A and B give relatively reliable column
density estimates at the resolution of 250um data while also making use of the
longer wavelengths. For high signal-to-noise data, the results of Method B are
better correlated with the true column density, while Method A is less
sensitive to noise. When the cloud has internal heating, results of Method B
are consistent with those that would be obtained with high-resolution data.
Because of line-of-sight temperature variations, these underestimate the true
column density and, because of a favourable cancellation of errors, Method A
can sometimes give more correct values. Radiative transfer modelling, even with
very simple 3D cloud models, can provide better results. However, the
complexity of the models required for improvements increases rapidly with the
complexity and opacity of the clouds.Comment: 14 pages, Accepted to A&
Mapping of interstellar clouds with infrared light scattered from dust: TMC-1N
Mapping of near-infrared (NIR) scattered light is a recent method for the
study of interstellar clouds, complementing other, more commonly used methods,
like dust emission and extinction. Our goal is to study the usability of this
method on larger scale, and compare the properties of a filament using NIR
scattering and other methods. We also study the radiation field and differences
in grain emissivity between diffuse and dense areas. We have used scattered J,
H, and K band surface brightness WFCAM-observations to map filament TMC-1N in
Taurus, covering an area of 1dx1d corresponding to ~(2.44 pc)^2. We have
converted the data into optical depth and compared the results with NIR
extinction and Herschel observations of submm dust emission. We see the
filament in scattered light in all three NIR bands. We note that our WFCAM
observations in TMC-1N show notably lower intensity than previous results in
Corona Australis using the same method. We show that 3D radiative transfer
simulations predict similar scattered surface brightness levels as seen in the
observations. However, changing the assumptions about the background can change
the results of simulations notably. We derive emissivity by using optical depth
in the J band as an independent tracer of column density. We obtain opacity
sigma(250um) values 1.7-2.4x10^-25 cm^2/H, depending on assumptions of the
extinction curve, which can change the results by over 40%. These values are
twice as high as obtained for diffuse areas, at the lower limit of earlier
results for denser areas. We show that NIR scattering can be a valuable tool in
making high resolution maps. We conclude, however, that NIR scattering
observations can be complicated, as the data can show relatively low-level
artefacts. This suggests caution when planning and interpreting the
observations.Comment: abstract shortened and figures reduced for astrop
Profiles of interstellar cloud filaments. Observational effects in synthetic sub-millimetre observations
Sub-millimetre observations suggest that the filaments of interstellar clouds
have rather uniform widths and can be described with the so-called Plummer
profiles. The shapes of the filament profiles are linked to their physical
state. Before drawing conclusions on the observed column density profiles, we
must evaluate the observational uncertainties. We want to estimate the bias
that could result from radiative transfer effects or from variations of submm
dust emissivity. We use cloud models obtained with magnetohydrodynamic
simulations and carry out radiative transfer calculations to produce maps of
sub-millimetre emission. Column densities are estimated based on the synthetic
observations. For selected filaments, the estimated profiles are compared to
those derived from the original column density. Possible effects from spatial
variations of dust properties are examined. With instrumental noise typical of
the Herschel observations, the parameters derived for nearby clouds are correct
to within a few percent. The radiative transfer effects have only a minor
effect on the results. If the signal-to-noise ratio is degraded by a factor of
four, the errors become significant and for half of the examined filaments the
values cannot be constrained. The errors increase in proportion to the cloud
distance. Assuming the resolution of Herschel instruments, the model filaments
are barely resolved at a distance of ~400 pc and the errors in the parameters
of the Plummer function are several tens of per cent. The Plummer parameters,
in particular the power-law exponent p, are sensitive to noise but can be
determined with good accuracy using Herschel data. One must be cautious about
possible line-of-sight confusion. In our models, a large fraction of the
filaments seen in the column density maps are not continuous structures in
three dimensions.Comment: 12 pages, 14 figures, accepted to A&
Profiling filaments: comparing near-infrared extinction and submillimetre data in TMC-1
Interstellar filaments are an important part of star formation. To understand
the structure of filaments, cross-section profiles are often fitted with
Plummer profiles. This profiling is often done with submm studies, such as
Herschel. It would be convenient if filament properties could also be studied
using groundbased NIR data. We compare the filament profiles obtained by NIR
extinction and submm observations to find out if reliable profiles can be
derived using NIR data. We use J-, H-, and K-band data of a filament north of
TMC-1 to derive an extinction map from colour excesses of background stars. We
compare the Plummer profiles obtained from extinction maps with Herschel dust
emission maps. We present 2 methods to estimate profiles from NIR: Plummer
profile fits to median Av of stars or directly to the Av of individual stars.
We compare the methods by simulations. In simulations extinction maps and the
new methods give correct results to within ~10-20 for modest densities. Direct
fit to data on individual stars gives more accurate results than extinction
map, and can work in higher density. In profile fits to real observations,
values of Plummer parameters are generally similar to within a factor of ~2.
Although parameter values can vary significantly, estimates of filament mass
usually remain accurate to within some tens of per cent. Our results for TMC-1
are in agreement with earlier results. High resolution NIR data give more
details, but 2MASS data can be used to estimate profiles. NIR extinction can be
used as an alternative to submm observations to profile filaments. Direct fits
of stars can also be a valuable tool. Plummer profile parameters are not always
well constrained, and caution should be taken when making fits. In the
evaluation of Plummer parameters, one can use the independence of dust emission
and NIR data and the difference in the shapes of the confidence regions.Comment: accepted to Astronomy & Astrophysics; abstract has been shortened for
astrop
Principal component-based image segmentation: a new approach to outline in vitro cell colonies
The in vitro clonogenic assay is a technique to study the ability of a cell
to form a colony in a culture dish. By optical imaging, dishes with stained
colonies can be scanned and assessed digitally. Identification, segmentation
and counting of stained colonies play a vital part in high-throughput screening
and quantitative assessment of biological assays. Image processing of such
pictured/scanned assays can be affected by image/scan acquisition artifacts
like background noise and spatially varying illumination, and contaminants in
the suspension medium. Although existing approaches tackle these issues, the
segmentation quality requires further improvement, particularly on noisy and
low contrast images. In this work, we present an objective and versatile
machine learning procedure to amend these issues by characterizing, extracting
and segmenting inquired colonies using principal component analysis, k-means
clustering and a modified watershed segmentation algorithm. The intention is to
automatically identify visible colonies through spatial texture assessment and
accordingly discriminate them from background in preparation for successive
segmentation. The proposed segmentation algorithm yielded a similar quality as
manual counting by human observers. High F1 scores (>0.9) and low
root-mean-square errors (around 14%) underlined good agreement with ground
truth data. Moreover, it outperformed a recent state-of-the-art method. The
methodology will be an important tool in future cancer research applications
Exhaust emissions of non-road mobile machine : Real-world and laboratory studies with diesel and HVO fuels
Exhaust emissions emitted by a non-road mobile machine were studied chasing a tractor in real-world conditions and repeating the same transient tests with a similar engine on an engine dynamometer where additionally, non-road steady state tests were carried out. The engines were equipped with an oxidation catalyst (DOC) and a selective catalytic reduction (SCR)system, and they were fuelled by fossil diesel fuel with ultra-low sulphur content and hydrotreated vegetable oil (HVO). By substituting diesel fuel with HVO the on-road emissions of nitrogen oxides (NOx) reduced 20% and particle number 44%, the emission factors being EFNOx =1.62 +/- 0.04 g/kWh and EFN = (28.2 +/- 7.8) x 10(13) #/kWh. Similar trend was observed for NOx at laboratory although the emissions were somewhat smaller than on-road. In contrast to real-world, in the laboratory experiment the EFN was only 2% smaller with HVO than with diesel, and these emission factors were almost one order of magnitude smaller than observed on-road. The number size distribution and volatility measurements showed that in real-world experiments small nucleation mode particles were formed during uphill and during downhill in engine braking conditions. These were not observed at laboratory. However, nucleation mode particles were observed in the laboratory experiments at high load steady driving conditions. At steady state tests the emissions strongly depended on engine load and engine speed with both fuels. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe
Multiwavelength study of the high-latitude cloud L1642: chain of star formation
L1642 is one of the two high galactic latitude (|b| > 30deg) clouds confirmed
to have active star formation. We examine the properties of this cloud,
especially the large-scale structure, dust properties, and compact sources in
different stages of star formation. We present high-resolution far-infrared and
submm observations with the Herschel and AKARI satellites and mm observations
with the AzTEC/ASTE telescope, which we combined with archive data from near-
and mid-infrared (2MASS, WISE) to mm observations (Planck). The Herschel
observations, combined with other data, show a sequence of objects from a cold
clump to young stellar objects at different evolutionary stages. Source B-3
(2MASS J04351455-1414468) appears to be a YSO forming inside the L1642 cloud,
instead of a foreground brown dwarf, as previously classified. Herschel data
reveal striation in the diffuse dust emission around L1642. The western region
shows striation towards NE and has a steeper column density gradient on its
southern side. The densest central region has a bow-shock like structure
showing compression from the west and a filamentary tail extending towards
east. The differences suggest that these may be spatially distinct structures,
aligned only in projection. We derive values of the dust emission cross-section
per H nucleon for different regions of the cloud. Modified black-body fits to
the spectral energy distribution of Herschel and Planck data give emissivity
spectral index beta values 1.8-2.0 for the different regions. The compact
sources have lower beta values and show an anticorrelation between T and beta.
Markov chain Monte Carlo calculations demonstrate the strong anticorrelation
between beta and T errors and the importance of mm Planck data in constraining
the estimates. L1642 reveals a more complex structure and sequence of star
formation than previously known.Comment: 22 pages, 18 figures, accepted to Astronomy & Astrophysics; abstract
shortened and figures reduced for astrop
Dietary Intake, Serum Hormone Concentrations, Amenorrhea and Bone Mineral Density of Physique Athletes and Active Gym Enthusiasts
As the diet, hormones, amenorrhea, and bone mineral density (BMD) of physique athletes (PA) and gym enthusiasts (GE) are little-explored, we studied those in 69 females (50 PA, 19 GE) and 20 males (11 PA, 9 GE). Energy availability (EA, kcal·kgFFMâ1·dâ1 in DXA) in female and male PA was ~41.3 and ~37.2, and in GE ~39.4 and ~35.3, respectively. Low EA (LEA) was found in 10% and 26% of female PA and GE, respectively, and in 11% of male GE. In PA, daily protein intake (g/kg body mass) was ~2.9â3.0, whereas carbohydrate and fat intakes were ~3.6â4.3 and ~0.8â1.0, respectively. PA had higher protein and carbohydrate and lower fat intakes than GE (p < 0.05). Estradiol, testosterone, IGF-1, insulin, leptin, TSH, T4, T3, cortisol, or BMD did not differ between PA and GE. Serum IGF-1 and leptin were explained 6% and 7%, respectively, by EA. In non-users of hormonal contraceptives, amenorrhea was found only in PA (27%) and was associated with lower fat percentage, but not EA, BMD, or hormones. In conclusion, off-season dietary intakes, hormone levels, and BMD meet the recommendations in most of the PA and GE. Maintaining too-low body fat during the off-season may predispose to menstrual disturbances
Dietary Intake, Serum Hormone Concentrations, Amenorrhea and Bone Mineral Density of Physique Athletes and Active Gym Enthusiasts
As the diet, hormones, amenorrhea, and bone mineral density (BMD) of physique athletes (PA) and gym enthusiasts (GE) are little-explored, we studied those in 69 females (50 PA, 19 GE) and 20 males (11 PA, 9 GE). Energy availability (EA, kcal·kgFFMâ1·dâ1 in DXA) in female and male PA was ~41.3 and ~37.2, and in GE ~39.4 and ~35.3, respectively. Low EA (LEA) was found in 10% and 26% of female PA and GE, respectively, and in 11% of male GE. In PA, daily protein intake (g/kg body mass) was ~2.9â3.0, whereas carbohydrate and fat intakes were ~3.6â4.3 and ~0.8â1.0, respectively. PA had higher protein and carbohydrate and lower fat intakes than GE (p < 0.05). Estradiol, testosterone, IGF-1, insulin, leptin, TSH, T4, T3, cortisol, or BMD did not differ between PA and GE. Serum IGF-1 and leptin were explained 6% and 7%, respectively, by EA. In non-users of hormonal contraceptives, amenorrhea was found only in PA (27%) and was associated with lower fat percentage, but not EA, BMD, or hormones. In conclusion, off-season dietary intakes, hormone levels, and BMD meet the recommendations in most of the PA and GE. Maintaining too-low body fat during the off-season may predispose to menstrual disturbances
- âŠ