46,491 research outputs found
The Effect of Scattering on Pulsar Polarization Angle
The low-frequency profiles of some pulsars manifest temporal broadening due
to scattering, usually accompanied by flat polarization position angle (PA)
curves. Assuming that the scattering works on the 4 Stokes parameters in the
same way, we have simulated the effect of scattering on polarization profiles
and find that the scattering can indeed flatten the PA curves. Since the
higher-frequency profiles suffer less from scattering, they are convolved with
scattering models to fit the observed low-frequency profiles. The calculated
flat PA curves exactly reproduce the corresponding observations.Comment: 4 pages. Accepted by A&
Discovery of a new supernova remnant G150.3+4.5
Large-scale radio continuum surveys have good potential for discovering new
Galactic supernova remnants (SNRs). Surveys of the Galactic plane are often
limited in the Galactic latitude of |b| ~ 5 degree. SNRs at high latitudes,
such as the Cygnus Loop or CTA~1, cannot be detected by surveys in such limited
latitudes. Using the available Urumqi 6 cm Galactic plane survey data, together
with the maps from the extended ongoing 6 cm medium latitude survey, we wish to
discover new SNRs in a large sky area. We searched for shell-like structures
and calculated radio spectra using the Urumqi 6 cm, Effelsberg 11 cm, and 21 cm
survey data. Radio polarized emission and evidence in other wavelengths are
also examined for the characteristics of SNRs. We discover an enclosed
oval-shaped object G150.3+4.5 in the 6 cm survey map. It is about 2.5 degree
wide and 3 degree high. Parts of the shell structures can be identified well in
the 11 cm, 21 cm, and 73.5 cm observations. The Effelsberg 21 cm total
intensity image resembles most of the structures of G150.3+4.5 seen at 6 cm,
but the loop is not closed in the northwest. High resolution images at 21 cm
and 73.5 cm from the Canadian Galactic Plane Survey confirm the extended
emission from the eastern and western shells of G150.3+4.5. We calculated the
radio continuum spectral indices of the eastern and western shells, which are
and between 6 cm and 21 cm, respectively.
The shell-like structures and their non-thermal nature strongly suggest that
G150.3+4.5 is a shell-type SNR. For other objects in the field of view,
G151.4+3.0 and G151.2+2.6, we confirm that the shell-like structure G151.4+3.0
very likely has a SNR origin, while the circular-shaped G151.2+2.6 is an HII
region with a flat radio spectrum, associated with optical filamentary
structure, H, and infrared emission.Comment: 5 pages, 3 figures, accepted for publication of Astronomy and
Astrophysic
Understanding of the Retarded Oxidation Effects in Silicon Nanostructures
In-depth understanding of the retarded oxidation phenomenon observed during
the oxidation of silicon nanostructures is proposed. The wet thermal oxidation
of various silicon nanostructures such as nanobeams, concave/convex nanorings
and nanowires exhibits an extremely different and complex behavior. Such
effects have been investigated by the modeling of the mechanical stress
generated during the oxidation process explaining the retarded regime. The
model describes the oxidation kinetics of silicon nanowires down to a few
nanometers while predicting reasonable and physical stress levels at the
Si/SiO interface by correctly taking into account the relaxation effects
in silicon oxide through plastic flow
Macroscopical Entangled Coherent State Generator in V configuration atom system
In this paper, we propose a scheme to produce pure and macroscopical
entangled coherent state. When a three-level ''V'' configuration atom interacts
with a doubly reasonant cavity, under the strong classical driven condition,
entangled coherent state can be generated from vacuum fields. An analytical
solution for this system under the presence of cavity losses is also given
A Sino-German 6cm polarisation survey of the Galactic plane - VIII. Small-diameter sources
Information of small-diameter sources is extracted from the Sino-German 6cm
polarisation survey of the Galactic plane carried out with the Urumqi 25-m
telescope. We performed two-dimensional elliptical Gaussian fits to the 6cm
maps to obtain a list of sources with total-intensity and polarised flux
densities. The source list contains 3832 sources with a fitted diameter smaller
than 16 arcmin and a peak flux density exceeding 30 mJy, so about 5 times the
rms noise, of the total-intensity data. The cumulative source count indicates
completeness for flux densities exceeding about 60 mJy. We identify 125
linearly polarised sources at 6cm with a peak polarisation flux density greater
than 10 mJy, so about 3 times the rms noise, of the polarised-intensity data.
Despite lacking compact steep spectrum sources, the 6cm catalogue lists about
20 percent more sources than the Effelsberg 21cm source catalogue at the same
angular resolution and for the same area. Most of the faint 6cm sources must
have a flat spectrum and are either HII regions or extragalactic. When compared
with the Green Bank 6cm (GB6) catalogue, we obtain higher flux densities for a
number of extended sources with complex structures. Polarised 6cm sources
density are uniformly distributed in Galactic latitude. Their number density
decreases towards the inner Galaxy. More than 80 percent of the polarised
sources are most likely extragalactic. With a few exceptions, the sources have
a higher percentage polarisation at 6cm than at 21cm. Depolarisation seems to
occur mostly within the sources with a minor contribution from the Galactic
foreground emission.Comment: A&A accepted, 9 pages, 5 figures, Tables 1 and 2 are accessible from
http://zmtt.bao.ac.cn/6cm
Effect of polymer concentration and length of hydrophobic end block on the unimer-micelle transition broadness in amphiphilic ABA symmetric triblock copolymer solutions
The effects of the length of each hydrophobic end block N_{st} and polymer
concentration \bar{\phi}_{P} on the transition broadness in amphiphilic ABA
symmetric triblock copolymer solutions are studied using the self-consistent
field lattice model. When the system is cooled, micelles are observed, i.e.,the
homogenous solution (unimer)-micelle transition occurs. When N_{st} is
increased, at fixed \bar{\phi}_{P}, micelles occur at higher temperature, and
the temperature-dependent range of micellar aggregation and half-width of
specific heat peak for unimer-micelle transition increase monotonously.
Compared with associative polymers, it is found that the magnitude of the
transition broadness is determined by the ratio of hydrophobic to hydrophilic
blocks, instead of chain length. When \bar{\phi}_{P} is decreased, given a
large N_{st}, the temperature-dependent range of micellar aggregation and
half-width of specific heat peak initially decease, and then remain nearly
constant. It is shown that the transition broadness is concerned with the
changes of the relative magnitudes of the eductions of nonstickers and solvents
from micellar cores.Comment: 8 pages, 4 figure
A Sino-German 6cm polarisation survey of the Galactic plane IX. HII regions
Large-scale radio continuum surveys provide data to get insights into the
physical properties of radio sources. HII regions are prominent radio sources
produced by thermal emission of ionised gas around young massive stars. We
identify and analyse HII regions in the Sino-German 6cm polarisation survey of
the Galactic plane. Objects with flat radio continuum spectra together with
infrared and/or Halpha emission were identified as HII regions. For HII regions
with small apparent sizes, we cross-matched the 6cm small-diameter source
catalogue with the radio HII region catalogue compiled by Paladini and the
infrared HII region catalogue based on the WISE data. Extended HII regions were
identified by eye by overlaying the Paladini and the WISE HII regions onto the
6cm survey images for coincidences. The TT-plot method was employed for
spectral index verification. A total of 401 HII regions were identified and
their flux densities were determined with the Sino-German 6cm survey data. In
the surveyed area, 76 pairs of sources are found to be duplicated in the
Paladini HII region catalogue, mainly due to the non-distinction of previous
observations with different angular resolutions, and 78 objects in their
catalogue are misclassified as HII regions, being actually planetary nebulae,
supernova remnants or extragalactic sources that have steep spectra. More than
30 HII regions and HII region candidates from our 6cm survey data, especially
extended ones, do not have counterparts in the WISE HII region catalogue, of
which 9 are identified for the first time. Based on the newly derived radio
continuum spectra and the evidence of infrared emission, the previously
identified SNRs G11.1-1.0, G20.4+0.1 and G16.4-0.5 are believed to be HII
regions.Comment: version after some minor corrections and language editing, full Table
2 - 5 will appear in CDS, accepted for publication in A&
- …