203 research outputs found
Local Entanglement and quantum phase transition in spin models
Due to the phase interference of electromagnetic wave, one can recover the
total image of one object from a small piece of holograph, which records the
interference pattern of two laser light reflected from it. Similarly, the
quantum superposition principle allows us to derive the global phase diagram of
quantum spin models by investigating a proper local measurement. In the present
paper, we study the two-site entanglement in the antifferomagnetic spin models
with both spin-1/2 and 1. We show that its behaviors reveal some important
information on the global properties and the quantum phase transition of these
systems.Comment: 6 pages, 7 figure
Entanglement and quantum phase transitions
We examine several well known quantum spin models and categorize behavior of
pairwise entanglement at quantum phase transitions. A unified picture on the
connection between the entanglement and quantum phase transition is given.Comment: 4 pages, 3 figure
Reaction-Diffusion-Branching Models of Stock Price Fluctuations
Several models of stock trading [P. Bak et al, Physica A {\bf 246}, 430
(1997)] are analyzed in analogy with one-dimensional, two-species
reaction-diffusion-branching processes. Using heuristic and scaling arguments,
we show that the short-time market price variation is subdiffusive with a Hurst
exponent . Biased diffusion towards the market price and blind-eyed
copying lead to crossovers to the empirically observed random-walk behavior
() at long times. The calculated crossover forms and diffusion constants
are shown to agree well with simulation data.Comment: 4 pages, 3 figure
The ground state entanglement in the model
In this paper, we investigate spin entanglement in the model defined on
a -dimensional bipartite lattice. The concurrence, a measure of the
entanglement between two spins, is analyzed. We prove rigorously that the
ground state concurrence reaches maximum at the isotropic point. For
dimensionality , the concurrence develops a cusp at the isotropic
point and we attribute it to the existence of magnetic long-range order.Comment: 5 pages, 2 figure
Constrain on possible pairing symmetry in a two-orbital model of FeAs-based superconductors
In this work, we establish a few exact identities through commutation of
intra-orbital and inter-orbital on-site pairings with a two-orbital model
describing newly discovered FeAs-based superconductors. Applying the conclusion
drawn from rigorous relation and physical interpretation, we give constraints
on the possible symmetries of the superconducting pairing of the model. Hence
the favorable pairings in newly discovered high-temperature oxypnictide
superconductors are proposed.Comment: 5 pages, 2 figure
Matrix Product State and Quantum Phase Transitions in the One-Dimensional Extended Quantum Compass Model
The matrix product state (MPS) is utilized to study the ground state
properties and quantum phase transitions (QPTs) of the one-dimensional quantum
compass model (QCM). The MPS wavefunctions are argued to be very efficient
descriptions of QCM ground states, and are numerically determined by imaginary
time projections. The ground state energy, correlations, quantum entanglement
and its spectrum, local and nonlocal order parameters, etc., are calculated and
studied in details. It is revealed that the bipartite and block entanglement
entropies, as well as the nearest neighbor correlation functions can be used to
detect the second-order QPTs, but not the first-order ones, while fidelity
detections can recognize both. The entanglement spectrum is extracted from the
MPS wavefunction, and found to be doubly degenerate in disordered phases of
QCM, where non-local string order parameters exist. Moreover, with linearized
tensor renormalization group method, the specific heat curves are evaluated and
their low temperature behaviors are investigated.Comment: 12 pages, 19 figure
Some exact results for the multicomponent t-J model
We present a generalization of the Sutherland's multicomponent model. Our
extension includes both the ferromagnetic and the antiferromagnetic t-J model
for any value of the exchange coupling J and the hopping parameter t. We prove
rigorously that for one dimensional chains the ground-state of the generalized
model is non-degenerate. As a consequence, the ordering of energy levels of the
antiferromagnetic t-J model is determined. Our result rigorously proves and
extends the analysis carried out by Sutherland in establishing the phase
diagram of the model as a function of the number of components.Comment: 11 pages, RevTeX 3.0, no figure
Charged and spin-excitation gaps in half-filled strongly correlated electron systems: A rigorous result
By exploiting the particle-hole symmetries of the Hubbard model, the periodic
Anderson model and the Kondo lattice model at half-filling and applying a
generalized version of Lieb's spin-reflection positivity method, we show that
the charged gaps of these models are always larger than their spin excitation
gaps. This theorem confirms the previous results derived by either the
variational approach or the density renormalization group approach.Comment: 20 pages, no figur
Divergent Evolution of TRC Genes in Mammalian Niche Adaptation
Mammals inhabit a wide variety of ecological niches, which in turn can be affected by various ecological factors, especially in relation to immunity. The canonical TRC repertoire (TRAC, TRBC, TRGC, and TRDC) codes C regions of T cell receptor chains that form the primary antigen receptors involved in the activation of cellular immunity. At present, little is known about the correlation between the evolution of mammalian TRC genes and ecological factors. In this study, four types canonical of TRC genes were identified from 37 mammalian species. Phylogenetic comparative methods (phyANOVA and PGLS) and selective pressure analyses among different groups of ecological factors (habitat, diet, and sociality) were carried out. The results showed that habitat was the major ecological factor shaping mammalian TRC repertoires. Specifically, trade-off between TRGC numbers and positive selection of TRAC and the balanced evolutionary rates between TRAC and TRDC genes were speculated as two main mechanisms in adaption to habitat and sociality. Overall, our study suggested divergent mechanisms for the evolution of TRCs, prompting mammalian immunity adaptions within diverse niches
Osteocalcin Ameliorates Motor Dysfunction in a 6-Hydroxydopamine-Induced Parkinson’s Disease Rat Model Through AKT/GSK3β Signaling
Osteoblasts derived osteocalcin (OCN) is recently reported to be involved in dopaminergic neuronal development. As dopaminergic neuronal injury in the substantia nigra (SN) is a pathological hallmark of Parkinson’s disease (PD), we investigated whether OCN could exert protective effects on 6-hydroxydopamine (6-OHDA)-induced PD rat model. Our data showed that the OCN level in the cerebrospinal fluid (CSF) in PD rat models was significantly lower than that in controls. Intervention with OCN could improve the behavioral dysfunction in PD rat models and reduce the tyrosine hydroxylase (TH) loss in the nigrostriatal system. In addition, OCN could inhibit the astrocyte and microglia proliferation in the SN of PD rats. In vitro studies showed that OCN significantly ameliorated the neurotoxicity of 6-OHDA through the AKT/GSK3β signaling pathway. In summary, OCN plays a protective role against parkinsonian neurodegeneration in the PD rat model, suggesting a potential therapeutic use of OCN in PD
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