33,735 research outputs found
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
On the nature of the lightest scalar resonances
We briefly review the recent progresses in the new unitarization approach
being developed by us. Especially we discuss the large
scatterings by making use of the partial wave matrix parametrization form.
We find that the pole may move to the negative real axis on the second
sheet of the complex plane, therefore it raises the interesting question
that this `' pole may be related to the in the linear
model.Comment: Talk presented by Zheng at ``Quark Confinement and Hadron
Spectroscopy VI'', 21--25 Sept. 2004, Cagliari, Italy. 3 pages with 2 figure
Performance of Photosensors in the PandaX-I Experiment
We report the long term performance of the photosensors, 143 one-inch
R8520-406 and 37 three-inch R11410-MOD photomultipliers from Hamamatsu, in the
first phase of the PandaX dual-phase xenon dark matter experiment. This is the
first time that a significant number of R11410 photomultiplier tubes were
operated in liquid xenon for an extended period, providing important guidance
to the future large xenon-based dark matter experiments.Comment: v3 as accepted by JINST with modifications based on reviewers'
comment
Quantum ether: photons and electrons from a rotor model
We give an example of a purely bosonic model -- a rotor model on the 3D cubic
lattice -- whose low energy excitations behave like massless U(1) gauge bosons
and massless Dirac fermions. This model can be viewed as a ``quantum ether'': a
medium that gives rise to both photons and electrons. It illustrates a general
mechanism for the emergence of gauge bosons and fermions known as ``string-net
condensation.'' Other, more complex, string-net condensed models can have
excitations that behave like gluons, quarks and other particles in the standard
model. This suggests that photons, electrons and other elementary particles may
have a unified origin: string-net condensation in our vacuum.Comment: 10 pages, 6 figures, RevTeX4. Home page http://dao.mit.edu/~we
Quantum orders in an exact soluble model
We find all the exact eigenstates and eigenvalues of a spin-1/2 model on
square lattice: . We show
that the ground states for have different quantum orders
described by Z2A and Z2B projective symmetry groups. The phase transition at
represents a new kind of phase transitions that changes quantum orders
but not symmetry. Both the Z2A and Z2B states are described by lattice
gauge theories at low energies. They have robust topologically degenerate
ground states and gapless edge excitations.Comment: 4 pages, RevTeX4, More materials on topological/quantum orders and
quantum computing can be found in http://dao.mit.edu/~we
The sino-german 6cm polarization survey of the galactic plane: A summary
We have finished the 6cm polarization survey of the Galactic plane using the
Urumqi 25m radio telescope. It covers 10deg<l<230deg in Galactic longitude and
|b| <5deg in Galactic latitude. The new polarization maps not only reveal new
properties of the diffuse magnetized interstellar medium, but also are very
useful for studying individual objects such as Hii regions, which may act as
Faraday screens with strong regular magnetic fields inside, and supernova
remnants for their polarization properties and spectra. The high sensitivity of
the survey enables us to discover two new SNRs G178.2-4.2 and G25.3-2.1 and a
number of Hii regions.Comment: 10 pages, 1 figure. International Journal of Modern Physics:
Conference Series (IJMPCS) for Proceedings of 3rd Galileo-Xu Guangqi meetin
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A low-bandgap dimeric porphyrin molecule for 10% efficiency solar cells with small photon energy loss
Dimeric porphyrin molecules have great potential as donor materials for high performance bulk heterojunction organic solar cells (OSCs). Recently reported dimeric porphyrins bridged by ethynylenes showed power conversion efficiencies (PCEs) of more than 8%. In this study, we design and synthesize a new conjugated dimeric D-A porphyrin ZnP2BT-RH, in which the two porphyrin units are linked by an electron accepting benzothiadiazole (BT) unit. The introduction of the BT unit enhances the electron delocalization, resulting in a lower highest occupied molecular orbital (HOMO) energy level and an increased molar extinction coefficient in the near-infrared (NIR) region. The bulk heterojunction solar cells with ZnP2BT-RH as the donor material exhibit a high PCE of up to 10% with a low energy loss (Eloss) of only 0.56 eV. The 10% PCE is the highest for porphyrin-based OSCs with a conventional structure, and this Eloss is also the smallest among those reported for small molecule-based OSCs with a PCE higher than 10% to date
String and Membrane condensation on 3D lattices
In this paper, we investigate the general properties of lattice spin models
that have string and/or membrane condensed ground states. We discuss the
properties needed to define a string or membrane operator. We study three 3D
spin models which lead to Z_2 gauge theory at low energies. All the three
models are exactly soluble and produce topologically ordered ground states. The
first model contains both closed-string and closed-membrane condensations. The
second model contains closed-string condensation only. The ends of open-strings
behave like fermionic particles. The third model also has condensations of
closed membranes and closed strings. The ends of open strings are bosonic while
the edges of open membranes are fermionic. The third model contains a new type
of topological order.Comment: 10 pages, RevTeX
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