33,853 research outputs found
Projective construction of two-dimensional symmetry-protected topological phases with U(1), SO(3), or SU(2) symmetries
We propose a general approach to construct symmetry protected topological
(SPT) states i.e the short-range entangled states with symmetry) in 2D
spin/boson systems on lattice. In our approach, we fractionalize spins/bosons
into different fermions, which occupy nontrivial Chern bands. After the
Gutzwiller projection of the free fermion state obtained by filling the Chern
bands, we can obtain SPT states on lattice. In particular, we constructed a
U(1) SPT state of a spin-1 model, a SO(3) SPT state of a boson system with
spin-1 bosons and spinless bosons, and a SU(2) SPT state of a spin-1/2 boson
system. By applying the "spin gauge field" which directly couples to the spin
density and spin current of components, we also calculate the quantum
spin Hall conductance in each SPT state. The projective ground states can be
further studied numerically in the future by variational Monte Carlo etc.Comment: 7+ pages, accepted by Phys. Rev.
Performance Analysis of a Low-Interference N-Continuous OFDM Scheme
This paper investigates two issues of power spectrum density (PSD) and bit
error rate (BER) of an N-continuous orthogonal frequency division multiplexing
(NC-OFDM) aided low-interference time-domain scheme, when the smooth signal is
designed by the linear combination of basis signals truncated by a window.
Based on the relationship between the continuity and sidelobe decaying, the PSD
performance is first analyzed and compared, in terms of the highest derivative
order (HDO) N and the length of the smooth signal L. Since the high-order
derivative of the truncation window has the finite continuity, the N-continuous
signal has two finite continuities, which may have different continuous
derivative orders. In this case, we develop a close PSD expression by
introducing another smooth signal, which is also linearly combined by other
basis signals, to explain the sidelobe decaying related to N and L. Then, in
the context of BER, considering the multipath Rayleigh fading channel, based on
the effect of the delayed tail of the smooth signal to the received signal, we
provide a procedure for calculating the BER expressed in the form of an
asymptotic summation.Comment: 7 pages, 6 figure
Translation invariant topological superconductors on lattice
In this paper we introduce four Z_2 topological indices zeta_k=0,1 at
k=(0,0), (0,pi), (pi, 0), (pi, pi) characterizing 16 universal classes of 2D
superconducting states that have translation symmetry but may break any other
symmetries. The 16 classes of superconducting states are distinguished by their
even/odd numbers of fermions on even-by-even, even-by-odd, odd-by-even, and
odd-by-odd lattices. As a result, the 16 classes topological superconducting
states exist even for interacting systems. For non-interacting systems, we find
that zeta_k is the number of electrons on k=(0,0), (0,pi), (pi, 0), or (pi,pi)
orbitals (mod 2) in the ground state. For 3D superconducting states with only
translation symmetry, there are 256 different types of topological
superconductors.Comment: 4 pages, RevTeX
Novel Algorithms for LDD Motif Search
Background: Motifs are crucial patterns that have numerous applications including the identification of transcription factors and their binding sites, composite regulatory patterns, similarity between families of proteins, etc. Several motif models have been proposed in the literature. The (l,d)-motif model is one of these that has been studied widely. However, this model will sometimes report too many spurious motifs than expected. We interpret a motif as a biologically significant entity that is evolutionarily preserved within some distance. It may be highly improbable that the motif undergoes the same number of changes in each of the species. To address this issue, in this paper, we introduce a new model which is more general than (l,d)-motif model. This model is called (l,d1,d2)-motif model (LDDMS) and is NP-hard as well. We present three elegant as well as efficient algorithms to solve the LDDMS problem, i.e., LDDMS1, LDDMS2 and LDDMS3. They are all exact algorithms. Results: We did both theoretical analyses and empirical tests on these algorithms. Theoretical analyses demonstrate that our algorithms have less computational cost than the pattern driven approach. Empirical results on both simulated datasets and real datasets show that each of the three algorithms has some advantages on some (l,d1,d2) instances. Conclusions: We proposed LDDMS model which is more practically relevant. We also proposed three exact efficient algorithms to solve the problem. Besides, our algorithms can be nicely parallelized. We believe that the idea in this new model can also be extended to other motif search problems such as Edit-distance-based Motif Search (EMS) and Simple Motif Search (SMS)
Would the reputation and behaviour of the Chinese stock exchange be a disincentive to investors considering a Chinese REIT?
China has drawn the world’s attention with the emergence, rapid growth and increasing maturity of its real estate market in the past twenty years. Currently the world’s third largest economy, China was the second largest Asian country for commercial property transaction capital flows in 2006 (JLL, 2007). International investors have recently shown considerable interest regarding property investment in China, via both direct and indirect property and changes to the rules governing internal funds are likely to initiate high levels of effective demand from domestic institutions too. China is yet to develop a Real Estate Investment trust (REIT) market; despite this investment demand encouragement for development of pilot REITs by the PRC government has waxed and waned with political imperatives to manage market and economic volatility. Chinese REITs would theoretically provide the opportunity for investors to access Chinese “property” returns with liquidity and flexibility and might further play a significant role in stabilising the Chinese capital market in the medium and long term. The purpose of this paper is to examine whether the reputation and behaviour of the Chinese stock exchanges is a disincentive to investors considering a Chinese REIT. This is addressed firstly by assessing Chinese stock market volatility compared to that of the Hong Kong and Singapore stock exchanges. Secondly, a survey was used to explore Chinese domestic investors’ attitudes to investment in Chinese property REITs and their preferences amongst the three main Asian stock exchanges where Chinese REITs might potentially be available
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