43,608 research outputs found
Real-space recipes for general topological crystalline states
Topological crystalline states are short-range entangled states jointly
protected by onsite and crystalline symmetries. While the non-interacting limit
of these states, e.g., the topological crystalline insulators, have been
intensively studied in band theory and have been experimentally discovered, the
classification and diagnosis of their strongly interacting counterparts are
relatively less well understood. Here we present a unified scheme for
constructing all topological crystalline states, bosonic and fermionic, free
and interacting, from real-space "building blocks" and "connectors". Building
blocks are finite-size pieces of lower dimensional topological states protected
by onsite symmetries alone, and connectors are "glue" that complete the open
edges shared by two or multiple pieces of building blocks. The resulted
assemblies are selected against two physical criteria we call the "no-open-edge
condition" and the "bubble equivalence", which, respectively, ensure that each
selected assembly is gapped in the bulk and cannot be deformed to a product
state. The scheme is then applied to obtaining the full classification of
bosonic topological crystalline states protected by several onsite symmetry
groups and each of the 17 wallpaper groups in two dimensions and 230 space
groups in three dimensions. We claim that our real-space recipes give the
complete set of topological crystalline states for bosons and fermions, and
prove the boson case analytically using a spectral sequence expansion of group
cohomology.Comment: 17+44 pages, 7+1 figures, 0+2 tables. The content is the same as the
published version, but arranged differentl
Large-field CO(1--0) observations toward the Galactic historical supernova remnants: a large cavity around Tycho's supernova remnant
The investigation of the interaction between the supernova remnants (SNRs)
and interstellar gas is not only necessary to improve our knowledge of SNRs,
but also to understand the nature of the progenitor systems. As a part of the
Milky Way Imaging Scroll Painting CO line survey (MWISP), we study the
interstellar gas surrounding the Galactic historical SNRs, using the PMO
13.7-meter telescope. In this work, we present large-field
(32) and high-sensitivity CO(1-0) molecular line
observations toward Tycho's SNR. The CO observations reveal, from the outside
in, large molecular clouds, stream-like structures, and an inner rim around
Tycho's SNR. We derived the basic properties (column density, mass, and
kinematics) of these objects based on the CO observations. The large molecular
clouds individually show an arc toward the remnant center, outlining a large
cavity with radii of 0.30.6 (or 13 pc 27
pc at a distance of 2.5 kpc) around the remnant. The CO line broadenings and
asymmetries detected in the surrounding clouds, the observed expansion of the
cavity, in concert with enhanced CO(2-1)/(1-0) intensity ratio detected
in previous studies, suggest the interaction of the large cavity with a wind in
the region. After excluding the scenario of a large bubble produced by bright
massive stars, we suggest that the large cavity could be explained by accretion
wind from the progenitor system of Tycho's supernova. Nevertheless, the
possibility of the random distribution of a large cavity around Tycho's SNR
cannot be ruled out thus far. Further observations are needed to confirm the
physical association of the large cavity with Tycho's SNR.Comment: 15 pages, 9 figures, updated according to the A&A proo
Performance of multiple-input multiple-output wireless communications systems using distributed antennas
In this contribution we propose and investigate a multiple-input multiple-output (MIMO) wireless communications system, where multiple receive antennas are distributed in the area covered by a cellular cell and connected with the base-station (BS). We first analyze the total received power by the BS through the distributed antennas, when assuming that the mobile's signal is transmitted over lognormal shadowed Rayleigh fading channels. Then, the outage probability of the distributed antenna MIMO systems is investigated, when considering various antenna distribution patterns. Furthermore, space-time coding at the mobile transmitter is considered for enhancing the outage performance of the distributed antenna MIMO system. Our study and simulation results show that the outage performance of a distributed antenna MIMO system can be significantly improved, when either increasing the number of distributed receive antennas or increasing the number of mobile transmit antennas
Density Operator Description of Atomic Ordered Spatial Modes in Cavity QED
We present a quantum Monte-Carlo simulation for a pumped atom in a strong
coupling cavity with dissipation, where two ordered spatial modes are formed
for the atomic probability density, with the peaks distributed either only in
the odd sites or only in the even ones of the lattice formed by the cavity
field. A mixed state density operator model, which describes the coupling
between different atomic spatial modes and the corresponding cavity field
components, is proposed, which goes beyond the pure state interpretation. We
develop a new decomposition treatment to derive the atomic spatial modes as
well as the cavity field statistics from the simulation results for the steady
state. With this treatment, we also investigate the dynamical process for the
probabilities of the atomic spatial modes in the adiabatic limit. According to
the analysis of the fitting error between the simulation results and the
density operator model, the latter is a good description for the system
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