3,555 research outputs found
Geometric phase and quantum phase transition in an inhomogeneous periodic XY spin-1/2 model
The notion of geometric phase has been recently introduced to analyze the
quantum phase transitions of many-body systems from the geometrical
perspective. In this work, we study the geometric phase of the ground state for
an inhomogeneous period-two anisotropic XY model in a transverse field. This
model encompasses a group of familiar spin models as its special cases and
shows a richer critical behavior. The exact solution is obtained by mapping on
a fermionic system through the Jordan-Wigner transformation and constructing
the relevant canonical transformation to realize the diagonalization of the
Hamiltonian coupled in the -space. The results show that there may exist
more than one quantum phase transition point at some parameter regions and
these transition points correspond to the divergence or extremum properties of
the Berry curvature.Comment: 6 pages, 3 figures. As a backup of a previous work and some typos in
the published version are fixe
Abelian and Non-Abelian Quantum Geometric Tensor
We propose a generalized quantum geometric tenor to understand topological
quantum phase transitions, which can be defined on the parameter space with the
adiabatic evolution of a quantum many-body system. The generalized quantum
geometric tenor contains two different local measurements, the non-Abelian
Riemannian metric and the non-Abelian Berry curvature, which are recognized as
two natural geometric characterizations for the change of the ground-state
properties when the parameter of the Hamiltonian varies. Our results show the
symmetry-breaking and topological quantum phase transitions can be understood
as the singular behavior of the local and topological properties of the quantum
geometric tenor in the thermodynamic limit.Comment: 5 pages, 2 figure
The Classical Limit of Quantum Mechanics and the Fejer Sum of the Fourier Series Expansion of a Classical Quantity
In quantum mechanics, the expectation value of a quantity on a quantum state,
provided that the state itself gives in the classical limit a motion of a
particle in a definite path, in classical limit goes over to Fourier series
form of the classical quantity. In contrast to this widely accepted point of
view, a rigorous calculation shows that the expectation value on such a state
in classical limit exactly gives the Fej\'{e}r's arithmetic mean of the partial
sums of the Fourier series
Entanglement in spin-1/2 dimerized Heisenberg systems
We study entanglement in dimerized Heisenberg systems. In particular, we give
exact results of ground-state pairwise entanglement for the four-qubit model by
identifying a Z_2 symmetry. Although the entanglements cannot identify the
critical point of the system, the mean entanglement of nearest-neighbor qubits
really does, namely, it reaches a maximum at the critical point.Comment: Four pages, three figures, accepted in Communications in Theoretical
Physic
PERGA: A Paired-End Read Guided De Novo Assembler for Extending Contigs Using SVM and Look Ahead Approach
Since the read lengths of high throughput sequencing (HTS) technologies are short, de novo assembly which plays significant roles in many applications remains a great challenge. Most of the state-of-the-art approaches base on de Bruijn graph strategy and overlap-layout strategy. However, these approaches which depend on k-mers or read overlaps do not fully utilize information of paired-end and single-end reads when resolving branches. Since they treat all single-end reads with overlapped length larger than a fix threshold equally, they fail to use the more confident long overlapped reads for assembling and mix up with the relative short overlapped reads. Moreover, these approaches have not been special designed for handling tandem repeats (repeats occur adjacently in the genome) and they usually break down the contigs near the tandem repeats. We present PERGA (Paired-End Reads Guided Assembler), a novel sequence-reads-guided de novo assembly approach, which adopts greedy-like prediction strategy for assembling reads to contigs and scaffolds using paired-end reads and different read overlap size ranging from Omax to Omin to resolve the gaps and branches. By constructing a decision model using machine learning approach based on branch features, PERGA can determine the correct extension in 99.7% of cases. When the correct extension cannot be determined, PERGA will try to extend the contig by all feasible extensions and determine the correct extension by using look-ahead approach. Many difficult-resolved branches are due to tandem repeats which are close in the genome. PERGA detects such different copies of the repeats to resolve the branches to make the extension much longer and more accurate. We evaluated PERGA on both Illumina real and simulated datasets ranging from small bacterial genomes to large human chromosome, and it constructed longer and more accurate contigs and scaffolds than other state-of-the-art assemblers. PERGA can be freely downloaded at https://github.com/hitbio/PERGA.published_or_final_versio
Entanglement, quantum phase transition and scaling in XXZ chain
Motivated by recent development in quantum entanglement, we study relations
among concurrence , SU(2) algebra, quantum phase transition and
correlation length at the zero temperature for the XXZ chain. We find that at
the SU(2) point, the ground state possess the maximum concurrence. When the
anisotropic parameter is deformed, however, its value decreases. Its
dependence on scales as in the XY metallic
phase and near the critical point (i.e. ) of the Ising-like
insulating phase. We also study the dependence of on the correlation length
, and show that it satisfies near the critical point. For
different size of the system, we show that there exists a universal scaling
function of with respect to the correlation length .Comment: 4 pages, 3 figures. to appear in Phys. Rev.
A Cellular Automata Model with Probability Infection and Spatial Dispersion
In this article, we have proposed an epidemic model by using probability
cellular automata theory. The essential mathematical features are analyzed with
the help of stability theory. We have given an alternative modelling approach
for the spatiotemporal system which is more realistic and satisfactory from the
practical point of view. A discrete and spatiotemporal approach are shown by
using cellular automata theory. It is interesting to note that both size of the
endemic equilibrium and density of the individual increase with the increasing
of the neighborhood size and infection rate, but the infections decrease with
the increasing of the recovery rate. The stability of the system around the
positive interior equilibrium have been shown by using suitable Lyapunov
function. Finally experimental data simulation for SARS disease in China and a
brief discussion conclude the paper
The Euler Number of Bloch States Manifold and the Quantum Phases in Gapped Fermionic Systems
We propose a topological Euler number to characterize nontrivial topological
phases of gapped fermionic systems, which originates from the Gauss-Bonnet
theorem on the Riemannian structure of Bloch states established by the real
part of the quantum geometric tensor in momentum space. Meanwhile, the
imaginary part of the geometric tensor corresponds to the Berry curvature which
leads to the Chern number characterization. We discuss the topological numbers
induced by the geometric tensor analytically in a general two-band model. As an
example, we show that the zero-temperature phase diagram of a transverse field
XY spin chain can be distinguished by the Euler characteristic number of the
Bloch states manifold in a (1+1)-dimensional Bloch momentum space
Glycerol-3-phosphate acyltransferase 3 (OsGPAT3) is required for anther development and male fertility in rice
Lipid molecules are key structural components of plant male reproductive organs, such as the anther and pollen. Although advances have been made in the understanding of acyl lipids in plant reproduction, the metabolic pathways of other lipid compounds, particularly glycerolipids, are not fully understood. Here we report that an endoplasmic reticulum-localized enzyme, Glycerol-3-Phosphate Acyltransferase 3 (OsGPAT3), plays an indispensable role in anther development and pollen formation in rice. OsGPAT3 is preferentially expressed in the tapetum and microspores of the anther. Compared with wild-type plants, the osgpat3 mutant displays smaller, pale yellow anthers with defective anther cuticle, degenerated pollen with defective exine, and abnormal tapetum development and degeneration. Anthers of the osgpat3 mutant have dramatic reductions of all aliphatic lipid contents. The defective cuticle and pollen phenotype coincide well with the down-regulation of sets of genes involved in lipid metabolism and regulation of anther development. Taking these findings together, this work reveals the indispensable role of a monocot-specific glycerol-3-phosphate acyltransferase in male reproduction in rice.Xiao Men, Jianxin Shi, Wanqi Liang, Qianfei Zhang, Gaibin Lian, Sheng Quan, Lu Zhu, Zhijing Luo, Mingjiao Chen, Dabing Zhan
Multiparty simultaneous quantum identity authentication based on entanglement swapping
We present a multiparty simultaneous quantum identity authentication protocol
based on entanglement swapping. In our protocol, the multi-user can be
authenticated by a trusted third party simultaneously
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