56 research outputs found
Exact solution of the anisotropic special transition in the O(n) model in 2D
The effect of surface exchange anisotropies is known to play a important role
in magnetic critical and multicritical behavior at surfaces. We give an exact
analysis of this problem in d=2 for the O(n) model by using Coulomb gas,
conformal invariance and integrability techniques. We obtain the full set of
critical exponents at the anisotropic special transition--where the symmetry on
the boundary is broken down to O(n_1)xO(n-n_1)--as a function of n_1. We also
obtain the full phase diagram and crossover exponents. Crucial in this analysis
is a new solution of the boundary Yang-Baxter equations for loop models. The
appearance of the generalization of Schramm-Loewner Evolution SLE_{\kappa,\rho}
is also discussed.Comment: 4 pages, 2 figure
Exact and Scaling Form of the Bipartite Fidelity of the Infinite XXZ Chain
We find an exact expression for the bipartite fidelity f=|'|^2,
where |vac> is the vacuum eigenstate of an infinite-size antiferromagnetic XXZ
chain and |vac>' is the vacuum eigenstate of an infinite-size XXZ chain which
is split in two. We consider the quantity -ln(f) which has been put forward as
a measure of quantum entanglement, and show that the large correlation length
xi behaviour is consistent with a general conjecture -ln(f) ~ c/8 ln(xi), where
c is the central charge of the UV conformal field theory (with c=1 for the XXZ
chain). This behaviour is a natural extension of the existing conformal field
theory prediction of -ln(f) ~ c/8 ln(L) for a length L bipartite system with
0<< L <<xi.Comment: 6 page
Boundary operators in the O(n) and RSOS matrix models
We study the new boundary condition of the O(n) model proposed by Jacobsen
and Saleur using the matrix model. The spectrum of boundary operators and their
conformal weights are obtained by solving the loop equations. Using the
diagrammatic expansion of the matrix model as well as the loop equations, we
make an explicit correspondence between the new boundary condition of the O(n)
model and the "alternating height" boundary conditions in RSOS model.Comment: 29 pages, 4 figures; version to appear in JHE
Entanglement in gapless resonating valence bond states
We study resonating-valence-bond (RVB) states on the square lattice of spins
and of dimers, as well as SU(N)-invariant states that interpolate between the
two. These states are ground states of gapless models, although the
SU(2)-invariant spin RVB state is also believed to be a gapped liquid in its
spinful sector. We show that the gapless behavior in spin and dimer RVB states
is qualitatively similar by studying the R\'enyi entropy for splitting a torus
into two cylinders, We compute this exactly for dimers, showing it behaves
similarly to the familiar one-dimensional log term, although not identically.
We extend the exact computation to an effective theory believed to interpolate
among these states. By numerical calculations for the SU(2) RVB state and its
SU(N)-invariant generalizations, we provide further support for this belief. We
also show how the entanglement entropy behaves qualitatively differently for
different values of the R\'enyi index , with large values of proving a
more sensitive probe here, by virtue of exhibiting a striking even/odd effect.Comment: 44 pages, 14 figures, published versio
Boundary conformal field theories and loop models
We propose a systematic method to extract conformal loop models for rational
conformal field theories (CFT). Method is based on defining an ADE model for
boundary primary operators by using the fusion matrices of these operators as
adjacency matrices. These loop models respect the conformal boundary
conditions. We discuss the loop models that can be extracted by this method for
minimal CFTs and then we will give dilute O(n) loop models on the square
lattice as examples for these loop models. We give also some proposals for WZW
SU(2) models.Comment: 23 Pages, major changes! title change
Nested algebraic Bethe ansatz for open GL(N) spin chains with projected K-matrices
We consider an open spin chain model with GL(N) bulk symmetry that is broken
to GL(M) x GL(N-M) by the boundary, which is a generalization of a model
arising in string/gauge theory. We prove the integrability of this model by
constructing the corresponding commuting transfer matrix. This construction
uses operator-valued "projected" K-matrices. We solve this model for general
values of N and M using the nested algebraic Bethe ansatz approach, despite the
fact that the K-matrices are not diagonal. The key to obtaining this solution
is an identity based on a certain factorization property of the reduced
K-matrices into products of R-matrices. Numerical evidence suggests that the
solution is complete.Comment: 27 pages; v2: minor change; v3: references adde
Hierarchical structure in the orbital entanglement spectrum in Fractional Quantum Hall systems
We investigate the non-universal part of the orbital entanglement spectrum
(OES) of the nu = 1/3 fractional quantum Hall effect (FQH) ground-state with
Coulomb interactions. The non-universal part of the spectrum is the part that
is missing in the Laughlin model state OES whose level counting is completely
determined by its topological order. We find that the OES levels of the Coulomb
interaction ground-state are organized in a hierarchical structure that mimic
the excitation-energy structure of the model pseudopotential Hamiltonian which
has a Laughlin ground state. These structures can be accurately modeled using
Jain's "composite fermion" quasihole-quasiparticle excitation wavefunctions. To
emphasize the connection between the entanglement spectrum and the energy
spectrum, we also consider the thermodynamical OES of the model pseudopotential
Hamiltonian at finite temperature. The observed good match between the
thermodynamical OES and the Coulomb OES suggests a relation between the
entanglement gap and the true energy gap.Comment: 16 pages, 19 figure
The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin motifs) family
The ADAMTS (A Disintegrin and Metalloproteinase with Thrombospondin motifs) enzymes are secreted, multi-domain matrix-associated zinc metalloendopeptidases that have diverse roles in tissue morphogenesis and patho-physiological remodeling, in inflammation and in vascular biology. The human family includes 19 members that can be sub-grouped on the basis of their known substrates, namely the aggrecanases or proteoglycanases (ADAMTS1, 4, 5, 8, 9, 15 and 20), the procollagen N-propeptidases (ADAMTS2, 3 and 14), the cartilage oligomeric matrix protein-cleaving enzymes (ADAMTS7 and 12), the von-Willebrand Factor proteinase (ADAMTS13) and a group of orphan enzymes (ADAMTS6, 10, 16, 17, 18 and 19). Control of the structure and function of the extracellular matrix (ECM) is a central theme of the biology of the ADAMTS, as exemplified by the actions of the procollagen-N-propeptidases in collagen fibril assembly and of the aggrecanases in the cleavage or modification of ECM proteoglycans. Defects in certain family members give rise to inherited genetic disorders, while the aberrant expression or function of others is associated with arthritis, cancer and cardiovascular disease. In particular, ADAMTS4 and 5 have emerged as therapeutic targets in arthritis. Multiple ADAMTSs from different sub-groupings exert either positive or negative effects on tumorigenesis and metastasis, with both metalloproteinase-dependent and -independent actions known to occur. The basic ADAMTS structure comprises a metalloproteinase catalytic domain and a carboxy-terminal ancillary domain, the latter determining substrate specificity and the localization of the protease and its interaction partners; ancillary domains probably also have independent biological functions. Focusing primarily on the aggrecanases and proteoglycanases, this review provides a perspective on the evolution of the ADAMTS family, their links with developmental and disease mechanisms, and key questions for the future
Glutathione Provides a Source of Cysteine Essential for Intracellular Multiplication of Francisella tularensis
Francisella tularensis is a highly infectious bacterium causing the zoonotic disease tularemia. Its ability to multiply and survive in macrophages is critical for its virulence. By screening a bank of HimarFT transposon mutants of the F. tularensis live vaccine strain (LVS) to isolate intracellular growth-deficient mutants, we selected one mutant in a gene encoding a putative γ-glutamyl transpeptidase (GGT). This gene (FTL_0766) was hence designated ggt. The mutant strain showed impaired intracellular multiplication and was strongly attenuated for virulence in mice. Here we present evidence that the GGT activity of F. tularensis allows utilization of glutathione (GSH, γ-glutamyl-cysteinyl-glycine) and γ-glutamyl-cysteine dipeptide as cysteine sources to ensure intracellular growth. This is the first demonstration of the essential role of a nutrient acquisition system in the intracellular multiplication of F. tularensis. GSH is the most abundant source of cysteine in the host cytosol. Thus, the capacity this intracellular bacterial pathogen has evolved to utilize the available GSH, as a source of cysteine in the host cytosol, constitutes a paradigm of bacteria–host adaptation
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