677 research outputs found
Synthesis and transfection properties of a series of lipidic neamine derivatives
International audienceWith the view to develop novel bioinspired nonviral vectors for gene delivery, we synthesized a series of cationiclipids with a neamine headgroup, which incorporates rings I and II of the natural antibiotic aminoglycoside neomycin B. Indeed, we reasoned that neamine might constitute a straightforward and versatile building block for synthesizing a variety of lipophilic aminoglycosides and modulating their characteristics such as size, topology, lipophilicity, number of charges, and charge density. Neamine derivatives bearing long dialkyl chains, one or two neamine headgroups, and four to ten protonatable amine functions were prepared through the selective alkylation of the 4âČ- or 5-hydroxyl function in ring I and ring II of neamine, respectively. The transfection activity of the twelve derivatives synthesized was investigated in Vitro in gene transfection experiments using several mammalian cell lines. The results allowed us to unveil interesting structure-activity relationships and to identify a formulation incorporating a small neamine derivative as a highly efficient gene delivery system
Model Order Reduction applied to a linear Finite Element model of a squirrel cage induction machine based on POD approach
The Proper Orthogonal Decomposition (POD) approach is applied to a linear Finite Element (FE) model of a squirrel cage induction machine. In order to obtain a reduced model valid on the whole operating range, snapshots are extracted from the simulation of typical tests such as at locked rotor and at the synchronous speed. Then, the reduced model of the induction machine is used to simulate different operating points with variable rotation speed and the results are compared to the full FE model to show the effectiveness of the proposed approach
Model Order Reduction for Rotating Electrical Machines
The simulation of electric rotating machines is both computationally
expensive and memory intensive. To overcome these costs, model order reduction
techniques can be applied. The focus of this contribution is especially on
machines that contain non-symmetric components. These are usually introduced
during the mass production process and are modeled by small perturbations in
the geometry (e.g., eccentricity) or the material parameters. While model order
reduction for symmetric machines is clear and does not need special treatment,
the non-symmetric setting adds additional challenges. An adaptive strategy
based on proper orthogonal decomposition is developed to overcome these
difficulties. Equipped with an a posteriori error estimator the obtained
solution is certified. Numerical examples are presented to demonstrate the
effectiveness of the proposed method
Comprehensive analysis of a symbiotic candidate V503 Her
V503 Her was previously proposed as an eclipsing symbiotic candidate based on
photometric behavior and spectroscopic appearance indicating the composite
optical spectrum. To investigate its nature, we analyzed long-term photometric
observations covering one hundred years of its photometric history and new
low-resolution optical spectroscopic data, supplemented with the multifrequency
measurements collected from several surveys and satellites. Based on the
analysis presented in this paper, we claim that V503 Her is not an eclipsing
binary star. The optical and infrared wavelengths are dominated by a K-type
bright giant with an effective temperature of 4 500 K, luminosity of 1 900
L, and sub-solar metallicity on the asymptotic giant branch showing
semiregular complex multi-periodic pulsation behavior. V503 Her does not show
the characteristics of strongly interacting symbiotic variables, but some
pieces of evidence suggest that it could still be one of the 'hidden'
accreting-only symbiotic systems. However, the currently available data do not
allow us to fully confirm or constrain the parameters of a possible companion.Comment: 16 pages, 10 figures, 4 tables; accepted in the Astronomical Journa
Mapping the column density and dust temperature structure of IRDCs with Herschel
Infrared dark clouds (IRDCs) are cold and dense reservoirs of gas potentially
available to form stars. Many of these clouds are likely to be pristine
structures representing the initial conditions for star formation. The study
presented here aims to construct and analyze accurate column density and dust
temperature maps of IRDCs by using the first Herschel data from the Hi-GAL
galactic plane survey. These fundamental quantities, are essential for
understanding processes such as fragmentation in the early stages of the
formation of stars in molecular clouds. We have developed a simple
pixel-by-pixel SED fitting method, which accounts for the background emission.
By fitting a grey-body function at each position, we recover the spatial
variations in both the dust column density and temperature within the IRDCs.
This method is applied to a sample of 22 IRDCs exhibiting a range of angular
sizes and peak column densities. Our analysis shows that the dust temperature
decreases significantly within IRDCs, from background temperatures of 20-30 K
to minimum temperatures of 8-15 K within the clouds, showing that dense
molecular clouds are not isothermal. Temperature gradients have most likely an
important impact on the fragmentation of IRDCs. Local temperature minima are
strongly correlated with column density peaks, which in a few cases reach NH2 =
1 x 10^{23} cm^{-2}, identifying these clouds as candidate massive prestellar
cores. Applying this technique to the full Hi-GAL data set will provide
important constraints on the fragmentation and thermal properties of IRDCs, and
help identify hundreds of massive prestellar core candidates.Comment: Accepted for publication in A&A Herschel special issu
Correlation of gas dynamics and dust in the evolved filament G82.65-02.00
Context. The combination of line and continuum observations can provide vital insight into the formation and fragmentation of filaments and the initial conditions for star formation. We have carried out line observations to map the kinematics of an evolved, actively star forming filament G82.65-2.00. The filament was first identified from the Planck data as a region of particularly cold dust emission and was mapped at 100-500 mu m as a part of the Herschel key program Galactic Cold Cores. The Herschel observations cover the central part of the filament, corresponding to a filament length of similar to 12 pc at the assumed distance of 620 pc.& para;& para;Aims. CO observations show that the filament has an intriguing velocity field with several velocity components around the filament. In this paper, we study the velocity structure in detail, to quantify possible mass accretion rate onto the filament, and study the masses of the cold cores located in the filament.& para;& para;Methods. We have carried out line observations of several molecules, including CO isotopologues, HCO+, HCN, and CS with the Osaka 1.85 m telescope and the Nobeyama 45 m telescope. The spectral line data are used to derive velocity and column density information.& para;& para;Results. The observations reveal several velocity components in the field, with strongest line emission concentrated to velocity range similar to[3,5] km s(-1). The column density of molecular hydrogen along the filament varies from 1.0 to 2.3 x 10(22) cm(2). We have examined six cold clumps from the central part of the filament. The clumps have masses in the range 10-20 M circle dot (similar to 70 M circle dot in total) and are close to or above the virial mass. Furthermore, the main filament is heavily fragmented and most of the substructures have a mass lower than or close to the virial mass, suggesting that the filament is dispersing as a whole. Position-velocity maps of (CO)-C-12 and (CO)-C-13 lines indicate that at least one of the striations is kinematically connected to two of the clumps, potentially indicating mass accretion from the striation onto the main filament. We tentatively estimate the accretion rate to be M = 2.23 x 10(-6) M circle dot/yr.& para;& para;Conclusions. Our line observations have revealed two or possibly three velocity components connected to the filament G82.65-2.00 and putative signs of mass accretion onto the filament. The line observations combined with Herschel and WISE maps suggest a possible collision between two cloud components.Peer reviewe
Galactic interstellar filaments as probed by LOFAR and Planck
Recent Low Frequency Array (LOFAR) observations at 115-175 MHz of a field at
medium Galactic latitudes (centered at the bright quasar 3C196) have shown
striking filamentary structures in polarization that extend over more than 4
degrees across the sky. In addition, the Planck satellite has released full sky
maps of the dust emission in polarization at 353GHz. The LOFAR data resolve
Faraday structures along the line of sight, whereas the Planck dust
polarization maps probe the orientation of the sky projected magnetic field
component. Hence, no apparent correlation between the two is expected. Here we
report a surprising, yet clear, correlation between the filamentary structures,
detected with LOFAR, and the magnetic field orientation, probed by the Planck
satellite. This finding points to a common, yet unclear, physical origin of the
two measurements in this specific area in the sky. A number of follow-up multi-
frequency studies are proposed to shed light on this unexpected finding.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
Planck's Dusty GEMS: Gravitationally lensed high-redshift galaxies discovered with the Planck survey
We present an analysis of 11 bright far-IR/submm sources discovered through a
combination of the Planck survey and follow-up Herschel-SPIRE imaging. Each
source has a redshift z=2.2-3.6 obtained through a blind redshift search with
EMIR at the IRAM 30-m telescope. Interferometry obtained at IRAM and the SMA,
and optical/near-infrared imaging obtained at the CFHT and the VLT reveal
morphologies consistent with strongly gravitationally lensed sources.
Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 um
and 2 mm, respectively. All objects are bright, isolated point sources in the
18 arcsec beam of SPIRE at 250 um, with spectral energy distributions peaking
either near the 350 um or the 500 um bands of SPIRE, and with apparent
far-infrared luminosities of up to 3x10^14 L_sun. Their morphologies and sizes,
CO line widths and luminosities, dust temperatures, and far-infrared
luminosities provide additional empirical evidence that these are strongly
gravitationally lensed high-redshift galaxies. We discuss their dust masses and
temperatures, and use additional WISE 22-um photometry and template fitting to
rule out a significant contribution of AGN heating to the total infrared
luminosity. Six sources are detected in FIRST at 1.4 GHz. Four have flux
densities brighter than expected from the local far-infrared-radio correlation,
but in the range previously found for high-z submm galaxies, one has a deficit
of FIR emission, and 6 are consistent with the local correlation. The global
dust-to-gas ratios and star-formation efficiencies of our sources are
predominantly in the range expected from massive, metal-rich, intense,
high-redshift starbursts. An extensive multi-wavelength follow-up programme is
being carried out to further characterize these sources and the intense
star-formation within them.Comment: A&A accepte
A Broadband Study of Galactic Dust Emission
We have combined infrared data with HI, H2 and HII surveys in order to
spatially decompose the observed dust emission into components associated with
different phases of the gas. An inversion technique is applied. For the
decomposition, we use the IRAS 60 and 100 micron bands, the DIRBE 140 and 240
micron bands, as well as Archeops 850 and 2096 micron wavelengths. In addition,
we apply the decomposition to all five WMAP bands. We obtain longitude and
latitude profiles for each wavelength and for each gas component in carefully
selected Galactic radius bins.We also derive emissivity coefficients for dust
in atomic, molecular and ionized gas in each of the bins.The HI emissivity
appears to decrease with increasing Galactic radius indicating that dust
associated with atomic gas is heated by the ambient interstellar radiation
field (ISRF). By contrast, we find evidence that dust mixed with molecular
clouds is significantly heated by O/B stars still embedded in their progenitor
clouds. By assuming a modified black-body with emissivity law lambda^(-1.5), we
also derive the radial distribution of temperature for each phase of the gas.
All of the WMAP bands except W appear to be dominated by emission from
something other than normal dust, most likely a mixture of thermal
bremstrahlung from diffuse ionized gas, synchrotron emission and spinning dust.
Furthermore, we find indications of an emissivity excess at long wavelengths
(lambda > 850 micron) in the outer Galaxy (R > 8.9 kpc). This suggests either
the existence of a very cold dust component in the outer Galaxy or a
temperature dependence of the spectral emissivity index. Finally, it is shown
that ~ 80% of the total FIR luminosity is produced by dust associated with
atomic hydrogen, in agreement with earlier findings by Sodroski et al. (1997).Comment: accepted for publication by A&
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