24,598 research outputs found
Exploring molecular complexity with ALMA (EMoCA): Detection of three new hot cores in Sagittarius B2(N)
The SgrB2 molecular cloud contains several sites forming high-mass stars.
SgrB2(N) is one of its main centers of activity. It hosts several compact and
UCHII regions, as well as two known hot molecular cores (SgrB2(N1) and
SgrB2(N2)), where complex organic molecules are detected. Our goal is to use
the high sensitivity of ALMA to characterize the hot core population in
SgrB2(N) and shed a new light on the star formation process. We use a complete
3 mm spectral line survey conducted with ALMA to search for faint hot cores in
SgrB2(N). We report the discovery of three new hot cores that we call
SgrB2(N3), SgrB2(N4), and SgrB2(N5). The three sources are associated with
class II methanol masers, well known tracers of high-mass star formation, and
SgrB2(N5) also with a UCHII region. The chemical composition of the sources and
the column densities are derived by modelling the whole spectra under the
assumption of LTE. The H2 column densities are computed from ALMA and SMA
continuum emission maps. The H2 column densities of these new hot cores are
found to be 16 up to 36 times lower than the one of the main hot core Sgr
B2(N1). Their spectra have spectral line densities of 11 up to 31 emission
lines per GHz, assigned to 22-25 molecules. We derive rotational temperatures
around 140-180 K for the three new hot cores and mean source sizes of 0.4 for
SgrB2(N3) and 1.0 for SgrB2(N4) and SgrB2(N5). SgrB2(N3) and SgrB2(N5) show
high velocity wing emission in typical outflow tracers, with a bipolar
morphology in their integrated intensity maps suggesting the presence of an
outflow, like in SgrB2(N1). The associations of the hot cores with class II
methanol masers, outflows, and/or UCHII regions tentatively suggest the
following age sequence: SgrB2(N4), SgrB2(N3), SgrB2(N5), SgrB2(N1). The status
of SgrB2(N2) is unclear. It may contain two distinct sources, a UCHII region
and a very young hot core.Comment: Accepted for publication in A&A, 24 pages, 23 figure
Softening of the stiffness of bottlebrush polymers by mutual interaction
We study bottlebrush macromolecules in a good solvent by small-angle neutron
scattering (SANS), static light scattering (SLS), and dynamic light scattering
(DLS). These polymers consist of a linear backbone to which long side chains
are chemically grafted. The backbone contains about 1600 monomer units (weight
average) and every second monomer unit carries side-chains with ca. 60 monomer
units. The SLS- and SANS data extrapolated to infinite dilution lead to the
form factor of the polymer that can be described in terms of a worm-like chain
with a contour length of 380 nm and a persistence length of 17.5 nm. An
analysis of the DLS data confirm these model parameters. The scattering
intensities taken at finite concentration can be modeled using the polymer
reference interaction site model. It reveals a softening of the bottlebrush
polymers caused by their mutual interaction. We demonstrate that the
persistence decreases from 17.5 nm down to 5 nm upon increasing the
concentration from dilute solution to the highest concentration 40.59 g/l under
consideration. The observed softening of the chains is comparable to the
theoretically predicted decrease of the electrostatic persistence length of
linear polyelectrolyte chains at finite concentrations.Comment: 4 pages, 4 figure
Real-Time Operating System/360
RTOS has a cost savings advantage for real-time applications, such as those with random inputs requiring a flexible data routing facility, display systems simplified by a device independent interface language, and complex applications needing added storage protection and data queuing
Optical-NIR spectroscopy of the puzzling gamma-ray source 3FGL 1603.9-4903/PMN J1603-4904 with X-shooter
The Fermi/LAT instrument has detected about two thousands Extragalactic High
Energy (E > 100 MeV) gamma-ray sources. One of the brightest is 3FGL
1603.9-4903, associated to the radio source PMN J1603-4904. Its nature is not
yet clear, it could be either a very peculiar BL Lac or a CSO (Compact
Symmetric Object) radio source, considered as the early stage of a radio
galaxy. The latter, if confirmed, would be the first detection in gamma-rays
for this class of objects. Recently a redshift z=0.18 +/- 0.01 has been claimed
on the basis of the detection of a single X-ray line at 5.44 +/- 0.05 keV
interpreted as a 6.4 keV (rest frame) fluorescent line. We aim to investigate
the nature of 3FGL 1603.9-4903/PMN J1603-4904 using optical to NIR
spectroscopy. We observed PMN J1603-4904 with the UV-NIR VLT/X-shooter
spectrograph for two hours. We extracted spectra in the VIS and NIR range that
we calibrated in flux and corrected for telluric absorption and we
systematically searched for absorption and emission features. The source was
detected starting from ~6300 Ang down to 24000 Ang with an intensity comparable
to the one of its 2MASS counterpart and a mostly featureless spectrum. The
continuum lacks absorption features and thus is non-stellar in origin and
likely non-thermal. On top of this spectrum we detected three emission lines
that we interpret as the Halpha-[NII] complex, the [SII] 6716,6731 doublet and
the [SIII] 9530 line, obtaining a redshift estimate of z= 0.2321 +/- 0.0004.
The equivalent width of the Halpha-[NII] complex implies that PMN J1603-4904
does not follow the observational definition of BL Lac, the line ratios suggest
that a LINER/Seyfert nucleus is powering the emission. This new redshift
measurement implies that the X-ray line previously detected should be
interpreted as a 6.7 keV line which is very peculiar.Comment: Published in Astronomy and Astrophysic
Noisy traveling waves: effect of selection on genealogies
For a family of models of evolving population under selection, which can be
described by noisy traveling wave equations, the coalescence times along the
genealogical tree scale like , where is the size of the
population, in contrast with neutral models for which they scale like . An
argument relating this time scale to the diffusion constant of the noisy
traveling wave leads to a prediction for which agrees with our
simulations. An exactly soluble case gives trees with statistics identical to
those predicted for mean-field spin glasses in Parisi's theory.Comment: 4 pages, 2 figures New version includes more numerical simulations
and some rewriting of the text presenting our result
Beam-Normal Single Spin Asymmetry in Elastic Electron Scattering off Si and Zr
We report on a new measurement of the beam-normal single spin asymmetry
in the elastic scattering of 570 MeV transversely polarized
electrons off Si and Zr at . The
studied kinematics allow for a comprehensive comparison with former results on
C. No significant mass dependence of the beam-normal single spin
asymmetry is observed in the mass regime from C to Zr.Comment: Submitted for publication to Physics Letters
Unbiased retrieval of frequency-dependent mechanical properties from noisy time-dependent signals
The mechanical response of materials to dynamic loading is often quantified by the frequency-dependent complex modulus. Probing materials directly in the frequency domain faces technical challenges such as a limited range of frequencies, long measurement times, or small sample sizes. Furthermore, many biological samples, such as cells or tissues, can change their properties upon repetitive probing at different frequencies. Therefore, it is common practice to extract the material properties by fitting predefined mechanical models to measurements performed in the time domain. This practice, however, precludes the probing of unique and yet unexplored material properties. In this report, we demonstrate that the frequency-dependent complex modulus can be robustly retrieved in a model-independent manner directly from time-dependent stress-strain measurements. While applying a rolling average eliminates random noise and leads to a reliable complex modulus in the lower frequency range, a Fourier transform with a complex frequency helps to recover the material properties at high frequencies. Finally, by properly designing the probing procedure, the recovery of reliable mechanical properties can be extended to an even wider frequency range. Our approach can be used with many state-of-the-art experimental methods to interrogate the mechanical properties of biological and other complex materials
Decay of Superflow Confined in Thin Torus: A Realization of Tunneling Quantum Fields
The quantum nucleation of phase slips in neutral superfluids confined in a
thin torus is investigated by means of the collective coordinate method. We
have devised, with numerical justification, a certain collective coordinate to
describe the quantum nucleation process of a phase slip. Considering the
quantum fluctuation around the local minimum of the action, we calculate the
effective mass of the phase slip. Due to the coherence of the condensate
throughout the torus, the effective mass is proportional to the circumference L
of the torus, and the decay rate has a strong exponential L-dependence.Comment: 4 pages, 2 figures, REVTe
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