472 research outputs found
Exact evaluation of density matrix elements for the Heisenberg chain
We have obtained all the density matrix elements on six lattice sites for the
spin-1/2 Heisenberg chain via the algebraic method based on the quantum
Knizhnik-Zamolodchikov equations. Several interesting correlation functions,
such as chiral correlation functions, dimer-dimer correlation functions, etc...
have been analytically evaluated. Furthermore we have calculated all the
eigenvalues of the density matrix and analyze the eigenvalue-distribution. As a
result the exact von Neumann entropy for the reduced density matrix on six
lattice sites has been obtained.Comment: 33 pages, 4 eps figures, 3 author
A Q-operator for the twisted XXX model
Taking the isotropic limit in a recent representation theoretic construction
of Baxter's Q-operators for the XXZ model with quasi-periodic boundary
conditions we obtain new results for the XXX model. We show that quasi-periodic
boundary conditions are needed to ensure convergence of the Q-operator
construction and derive a quantum Wronskian relation which implies two
different sets of Bethe ansatz equations, one above the other below the
"equator" of total spin zero. We discuss the limit to periodic boundary
conditions at the end and explain how this construction might be useful in the
context of correlation functions on the infinite lattice. We also identify a
special subclass of solutions to the quantum Wronskian for chains up to a
length of 10 sites and possibly higher.Comment: 19 page
The Baxter's Q-operator for the W-algebra
The q-oscillator representation for the Borel subalgebra of the affine
symmetry is presented. By means of this q-oscillator
representation, we give the free field realizations of the Baxter's Q-operator
, for the W-algebra . We give the functional
relations of the - operators, including the higher-rank generalization of
the Baxter's - relation.Comment: LaTE
Balancing intestinal and systemic inflammation through cell type-specific expression of the aryl hydrocarbon receptor repressor
As a sensor of polyaromatic chemicals the aryl hydrocarbon receptor (AhR)
exerts an important role in immune regulation besides its requirement for
xenobiotic metabolism. Transcriptional activation of AhR target genes is
counterregulated by the AhR repressor (AhRR) but the exact function of the
AhRR in vivo is currently unknown. We here show that the AhRR is predominantly
expressed in immune cells of the skin and intestine, different from other AhR
target genes. Whereas AhRR antagonizes the anti-inflammatory function of the
AhR in the context of systemic endotoxin shock, AhR and AhRR act in concert to
dampen intestinal inflammation. Specifically, AhRR contributes to the
maintenance of colonic intraepithelial lymphocytes and prevents excessive IL-
1β production and Th17/Tc17 differentiation. In contrast, the AhRR enhances
IFN-γ-production by effector T cells in the inflamed gut. Our findings
highlight the physiologic importance of cell-type specific balancing of
AhR/AhRR expression in response to microbial, nutritional and other
environmental stimuli
Non-diagonal open spin-1/2 XXZ quantum chains by separation of variables: Complete spectrum and matrix elements of some quasi-local operators
The integrable quantum models, associated to the transfer matrices of the
6-vertex reflection algebra for spin 1/2 representations, are studied in this
paper. In the framework of Sklyanin's quantum separation of variables (SOV), we
provide the complete characterization of the eigenvalues and eigenstates of the
transfer matrix and the proof of the simplicity of the transfer matrix
spectrum. Moreover, we use these integrable quantum models as further key
examples for which to develop a method in the SOV framework to compute matrix
elements of local operators. This method has been introduced first in [1] and
then used also in [2], it is based on the resolution of the quantum inverse
problem (i.e. the reconstruction of all local operators in terms of the quantum
separate variables) plus the computation of the action of separate covectors on
separate vectors. In particular, for these integrable quantum models, which in
the homogeneous limit reproduce the open spin-1/2 XXZ quantum chains with
non-diagonal boundary conditions, we have obtained the SOV-reconstructions for
a class of quasi-local operators and determinant formulae for the
covector-vector actions. As consequence of these findings we provide one
determinant formulae for the matrix elements of this class of reconstructed
quasi-local operators on transfer matrix eigenstates.Comment: 40 pages. Minor modifications in the text and some notations and some
more reference adde
Cardiosphere-derived cells suppress allogeneic lymphocytes by production of PGE2 acting via the EP4 receptor
derived cells (CDCs) are a cardiac progenitor cell population, which have been shown to possess cardiac regenerative properties and can improve heart function in a variety of cardiac diseases. Studies in large animal models have predominantly focussed on using autologous cells for safety, however allogeneic cell banks would allow for a practical, cost-effective and efficient use in a clinical setting. The aim of this work was to determine the immunomodulatory status of these cells using CDCs and lymphocytes from 5 dogs. CDCs expressed MHC I but not MHC II molecules and in mixed lymphocyte reactions demonstrated a lack of lymphocyte proliferation in response to MHC-mismatched CDCs. Furthermore, MHC-mismatched CDCs suppressed lymphocyte proliferation and activation in response to Concanavalin A. Transwell experiments demonstrated that this was predominantly due
to direct cell-cell contact in addition to soluble mediators whereby CDCs produced high levels of PGE2
under inflammatory conditions. This led to down-regulation of CD25 expression on lymphocytes via the
EP4 receptor. Blocking prostaglandin synthesis restored both, proliferation and activation (measured via CD25 expression) of stimulated lymphocytes. We demonstrated for the first time in a large animal model that CDCs inhibit proliferation in allo-reactive lymphocytes and have potent immunosuppressive activity mediated via PGE2
Form factors of integrable Heisenberg (higher) spin chains
We present determinant formulae for the form factors of spin operators of
general integrable XXX Heisenberg spin chains for arbitrary (finite
dimensional) spin representations. The results apply to any "mixed" spin
chains, such as alternating spin chains, or to spin chains with magnetic
impurities.Comment: 24 page
Energy spectra of fractional quantum Hall systems in the presence of a valence hole
The energy spectrum of a two-dimensional electron gas (2DEG) in the
fractional quantum Hall regime interacting with an optically injected valence
band hole is studied as a function of the filling factor and the
separation between the electron and hole layers. The response of the 2DEG
to the hole changes abruptly at of the order of the magnetic length
. At , the hole binds electrons to form neutral () or
charged () excitons, and the photoluminescence (PL) spectrum probes the
lifetimes and binding energies of these states rather than the original
correlations of the 2DEG. The ``dressed exciton'' picture (in which the
interaction between an exciton and the 2DEG was proposed to merely enhance the
exciton mass) is questioned. Instead, the low energy states are explained in
terms of Laughlin correlations between the constituent fermions (electrons and
's) and the formation of two-component incompressible fluid states in the
electron--hole plasma. At , the hole binds up to two Laughlin
quasielectrons (QE) of the 2DEG to form fractionally charged excitons
QE. The previously found ``anyon exciton'' QE is shown to be
unstable at any value of . The critical dependence of the stability of
different QE complexes on the presence of QE's in the 2DEG leads to the
observed discontinuity of the PL spectrum at or .Comment: 16 pages, 14 figures, submitted to PR
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