48,447 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&
Effect of distribution of stickers along backbone on temperature-dependent structural properties in associative polymer solutions
Effect of distribution of stickers along the backbone on structural
properties in associating polymer solutions is studied using self-consistent
field lattice model. Only two inhomogeneous morphologies, i.e.,
microfluctuation homogenous (MFH) and micelle morphologies, are observed. If
the system is cooled, the solvent content within the aggregates decreases. When
the spacing of stickers along the backbone is increased the
temperature-dependent range of aggregation in MFH morphology and half-width of
specific heat peak for homogenous solutions-MFH transition increase, and the
symmetry of the peak decreases. However, with increasing spacing of stickers,
the above three corresponding quantities related to micelles behave
differently. It is demonstrated that the broad nature of the observed
transitions can be ascribed to the structural changes which accompany the
replacement of solvents in aggregates by polymer, which is consistent with the
experimental conclusion. It is found that different effect of spacing of
stickers on the two transitions can be interpreted in terms of intrachain and
interchain associations.Comment: 10 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1202.459
The effect of asymmetry of the coil block on self-assembly in ABC coil-rod-coil triblock copolymers
Using the self-consistent field approach, the effect of asymmetry of the coil
block on the microphase separation is focused in ABC coil-rod-coil triblock
copolymers. For different fractions of the rod block , some stable
structures are observed, i.e., lamellae, cylinders, gyroid, and core-shell
hexagonal lattice, and the phase diagrams are constructed. The calculated
results show that the effect of the coil block fraction is
dependent on . When , the effect of asymmetry of
the coil block is similar to that of the ABC flexible triblock copolymers; When
, the self-assembly of ABC coil-rod-coil triblock copolymers
behaves like rod-coil diblock copolymers under some condition. When continues to increase, the effect of asymmetry of the coil block reduces.
For , under the symmetrical and rather asymmetrical
conditions, an increase in the interaction parameter between different
components leads to different transitions between cylinders and lamellae. The
results indicate some remarkable effect of the chain architecture on
self-assembly, and can provide the guidance for the design and synthesis of
copolymer materials.Comment: 9 pages, 3 figure
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
Superconductivity in Ti-doped Iron-Arsenide Compound Sr4Cr0.8Ti1.2O6Fe2As2
Superconductivity was achieved in Ti-doped iron-arsenide compound
Sr4Cr0.8Ti1.2O6Fe2As2 (abbreviated as Cr-FeAs-42622). The x-ray diffraction
measurement shows that this material has a layered structure with the space
group of \emph{P4/nmm}, and with the lattice constants a = b = 3.9003 A and c =
15.8376 A. Clear diamagnetic signals in ac susceptibility data and
zero-resistance in resistivity data were detected at about 6 K, confirming the
occurrence of bulk superconductivity. Meanwhile we observed a superconducting
transition in the resistive data with the onset transition temperature at 29.2
K, which may be induced by the nonuniform distribution of the Cr/Ti content in
the FeAs-42622 phase, or due to some other minority phase.Comment: 3 pages, 3 figure
Subdwarf B stars from the common envelope ejection channel
From the canonical binary scenario, the majority of sdBs are produced from
low-mass stars with degenerate cores where helium is ignited in a way of
flashes. Due to numerical difficulties, the models of produced sdBs are
generally constructed from more massive stars with non-degenerate cores,
leaving several uncertainties on the exact characteristics of sdB stars.
Employing MESA, we systematically studied the characteristics of sdBs produced
from the common envelope (CE) ejection channel, and found that the sdB stars
produced from the CE ejection channel appear to form two distinct groups on the
effective temperature-gravity diagram. One group (the flash-mixing model)
almost has no H-rich envelope and crows at the hottest temperature end of the
extremely horizontal branch (EHB), while the other group has significant H-rich
envelope and spreads over the whole canonical EHB region. The key factor for
the dichotomy of the sdB properties is the development of convection during the
first helium flash, which is determined by the interior structure of the star
after the CE ejection. For a given initial stellar mass and a given core mass
at the onset of the CE, if the CE ejection stops early, the star has a
relatively massive H-rich envelope, resulting in a canonical sdB generally. The
fact of only a few short-orbital-period sdB binaries being in the flash-mixing
sdB region and the lack of He-rich sdBs in short-orbital-period binaries
indicate that the flash mixing is not very often in the products of the CE
ejection. A falling back process after the CE ejection, similar to that
happened in nova, is an appropriate way of increasing the envelope mass, then
prevents the flash mixing.Comment: accepted by A&A 12 pages, 11 figure
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