72,004 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&
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
Supersolid and charge density-wave states from anisotropic interaction in an optical lattice
We show anisotropy of the dipole interaction between magnetic atoms or polar
molecules can stabilize new quantum phases in an optical lattice. Using a well
controlled numerical method based on the tensor network algorithm, we calculate
phase diagram of the resultant effective Hamiltonian in a two-dimensional
square lattice - an anisotropic Hubbard model of hard-core bosons with
attractive interaction in one direction and repulsive interaction in the other
direction. Besides the conventional superfluid and the Mott insulator states,
we find the striped and the checkerboard charge density wave states and the
supersolid phase that interconnect the superfluid and the striped solid states.
The transition to the supersolid phase has a mechanism different from the case
of the soft-core Bose Hubbard model.Comment: 5 pages, 5 figures
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Lamina-specific AMPA receptor dynamics following visual deprivation in vivo.
Regulation of AMPA receptor (AMPAR) expression is central to synaptic plasticity and brain function, but how these changes occur in vivo remains elusive. Here, we developed a method to longitudinally monitor the expression of synaptic AMPARs across multiple cortical layers in awake mice using two-photon imaging. We observed that baseline AMPAR expression in individual spines is highly dynamic with more dynamics in primary visual cortex (V1) layer 2/3 (L2/3) neurons than V1 L5 neurons. Visual deprivation through binocular enucleation induces a synapse-specific and depth-dependent change of synaptic AMPARs in V1 L2/3 neurons, wherein deep synapses are potentiated more than superficial synapses. The increase is specific to L2/3 neurons and absent on apical dendrites of L5 neurons, and is dependent on expression of the AMPAR-binding protein GRIP1. Our study demonstrates that specific neuronal connections, across cortical layers and even within individual neurons, respond uniquely to changes in sensory experience
Direct solar-pumped iodine laser amplifier
In order to evaluate the feasibility of the solar pumped dye laser, the parametric study of a dye laser amplifier pumped by a solar simulator and flashlamp was carried out, and the amplifier gains were measured at various pump beam irradiances on the dye cell. Rhodamine 6G was considered as a candidate for the solar pumped laser because of its good utilization of the solar spectrum and high quantum efficiency. The measurement shows that a solar concentration of 20,000 is required to reach the threshold of the dye. The work to construct a kinetic model algorithm which predicts the output parameter of laser was progressed. The kinetic model was improved such that there is good agreement between the theoretical model and experimental data for the systems defined previously as flashlamp pumped laser oscillator, and the long path length solar pumped laser
Direct solar-pumped iodine laser amplifier
The improvement on the collection system of the Tarmarack Solar Simulator beam was attemped. The basic study of evaluating the solid state laser materials for the solar pumping and also the work to construct a kinetic model algorithm for the flashlamp pumped iodine lasers were carried out. It was observed that the collector cone worked better than the lens assembly in order to collect the solar simulator beam and to focus it down to a strong power density. The study on the various laser materials and their lasing characteristics shows that the neodymium and chromium co-doped gadolinium scandium gallium garnet (Nr:Cr:GSGG) may be a strong candidate for the high power solar pumped solid state laser crystal. On the other hand the improved kinetic modeling for the flashlamp pumped iodine laser provides a good agreement between the theoretical model and the experimental data on the laser power output, and predicts the output parameters of a solar pumped iodine laser
Cross-Layer Peer-to-Peer Track Identification and Optimization Based on Active Networking
P2P applications appear to emerge as ultimate killer applications due to their ability to construct highly dynamic overlay topologies with rapidly-varying and unpredictable traffic dynamics, which can constitute a serious challenge even for significantly over-provisioned IP networks. As a result, ISPs are facing new, severe network management problems that are not guaranteed to be addressed by statically deployed network engineering mechanisms. As a first step to a more complete solution to these problems, this paper proposes a P2P measurement, identification and optimisation architecture, designed to cope with the dynamicity and unpredictability of existing, well-known and future, unknown P2P systems. The purpose of this architecture is to provide to the ISPs an effective and scalable approach to control and optimise the traffic produced by P2P applications in their networks. This can be achieved through a combination of different application and network-level programmable techniques, leading to a crosslayer identification and optimisation process. These techniques can be applied using Active Networking platforms, which are able to quickly and easily deploy architectural components on demand. This flexibility of the optimisation architecture is essential to address the rapid development of new P2P protocols and the variation of known protocols
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
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