24 research outputs found
Scaling properties at the interface between different critical subsystems: The Ashkin-Teller model
We consider two critical semi-infinite subsystems with different critical
exponents and couple them through their surfaces. The critical behavior at the
interface, influenced by the critical fluctuations of the two subsystems, can
be quite rich. In order to examine the various possibilities, we study a system
composed of two coupled Ashkin-Teller models with different four-spin couplings
epsilon, on the two sides of the junction. By varying epsilon, some bulk and
surface critical exponents of the two subsystems are continuously modified,
which in turn changes the interface critical behavior. In particular we study
the marginal situation, for which magnetic critical exponents at the interface
vary continuously with the strength of the interaction parameter. The behavior
expected from scaling arguments is checked by DMRG calculations.Comment: 10 pages, 9 figures. Minor correction
Numerical study of the critical behavior of the Ashkin-Teller model at a line defect
We consider the Ashkin-Teller model on the square lattice, which is
represented by two Ising models ( and ) having a four-spin
coupling of strength, , between them. We introduce an asymmetric
defect line in the system along which the couplings in the Ising model
are modified. In the Hamiltonian version of the model we study the scaling
behavior of the critical magnetization at the defect, both for and for
spins by density matrix renormalization. For we observe
identical scaling for and spins, whereas for one
model becomes locally ordered and the other locally disordered. This is
different of the critical behavior of the uncoupled model () and is
in contradiction with the results of recent field-theoretical calculations.Comment: 6 pages, 4 figure
Boundary critical behaviour of two-dimensional random Ising models
Using Monte Carlo techniques and a star-triangle transformation, Ising models
with random, 'strong' and 'weak', nearest-neighbour ferromagnetic couplings on
a square lattice with a (1,1) surface are studied near the phase transition.
Both surface and bulk critical properties are investigated. In particular, the
critical exponents of the surface magnetization, 'beta_1', of the correlation
length, 'nu', and of the critical surface correlations, 'eta_{\parallel}', are
analysed.Comment: 16 pages in ioplppt style, 7 ps figures, submitted to J. Phys.
Percolation and Conduction in Restricted Geometries
The finite-size scaling behaviour for percolation and conduction is studied
in two-dimensional triangular-shaped random resistor networks at the
percolation threshold. The numerical simulations are performed using an
efficient star-triangle algorithm. The percolation exponents, linked to the
critical behaviour at corners, are in good agreement with the conformal
results. The conductivity exponent, t', is found to be independent of the shape
of the system. Its value is very close to recent estimates for the surface and
bulk conductivity exponents.Comment: 10 pages, 7 figures, TeX, IOP macros include
Griffiths-McCoy singularities in random quantum spin chains: Exact results through renormalization
The Ma-Dasgupta-Hu renormalization group (RG) scheme is used to study
singular quantities in the Griffiths phase of random quantum spin chains. For
the random transverse-field Ising spin chain we have extended Fisher's
analytical solution to the off-critical region and calculated the dynamical
exponent exactly. Concerning other random chains we argue by scaling
considerations that the RG method generally becomes asymptotically exact for
large times, both at the critical point and in the whole Griffiths phase. This
statement is checked via numerical calculations on the random Heisenberg and
quantum Potts models by the density matrix renormalization group method.Comment: 4 pages RevTeX, 2 figures include
Disorder Induced Phases in Higher Spin Antiferromagnetic Heisenberg Chains
Extensive DMRG calculations for spin S=1/2 and S=3/2 disordered
antiferromagnetic Heisenberg chains show a rather distinct behavior in the two
cases. While at sufficiently strong disorder both systems are in a random
singlet phase, we show that weak disorder is an irrelevant perturbation for the
S=3/2 chain, contrary to what expected from a naive application of the Harris
criterion. The observed irrelevance is attributed to the presence of a new
correlation length due to enhanced end-to-end correlations. This phenomenon is
expected to occur for all half-integer S > 1/2 chains. A possible phase diagram
of the chain for generic S is also discussed.Comment: 6 Pages and 6 figures. Final version as publishe
Corner Exponents in the Two-Dimensional Potts Model
The critical behavior at a corner in two-dimensional Ising and three-state
Potts models is studied numerically on the square lattice using transfer
operator techniques. The local critical exponents for the magnetization and the
energy density for various opening angles are deduced from finite-size scaling
results at the critical point for isotropic or anisotropic couplings. The
scaling dimensions compare quite well with the values expected from conformal
invariance, provided the opening angle is replaced by an effective one in
anisotropic systems.Comment: 11 pages, 2 eps-figures, uses LaTex and eps
One Decade’s Research Efforts in Hungary to Develop a Bisexual Lure for the Cotton Bollworm Helicoverpa armigera Hübner
Surface critical behavior of random systems at the ordinary transition
We calculate the surface critical exponents of the ordinary transition
occuring in semi-infinite, quenched dilute Ising-like systems. This is done by
applying the field theoretic approach directly in d=3 dimensions up to the
two-loop approximation, as well as in dimensions. At
we extend, up to the next-to-leading order, the previous
first-order results of the expansion by Ohno and Okabe
[Phys.Rev.B 46, 5917 (1992)]. In both cases the numerical estimates for surface
exponents are computed using Pade approximants extrapolating the perturbation
theory expansions. The obtained results indicate that the critical behavior of
semi-infinite systems with quenched bulk disorder is characterized by the new
set of surface critical exponents.Comment: 11 pages, 11 figure
The impact of circulating preeclampsia-associated extracellular vesicles on the migratory activity and phenotype of THP-1 monocytic cells
Intercellular communication via extracellular vesicles (EVs) and their target cells, especially immune cells, results in functional and phenotype changes that consequently may play a significant role in various physiological states and the pathogenesis of immune-mediated disorders. Monocytes are the most prominent environment-sensing immune cells in circulation, skilled to shape their microenvironments via cytokine secretion and further differentiation. Both the circulating monocyte subset distribution and the blood plasma EV pattern are characteristic for preeclampsia, a pregnancy induced immune-mediated hypertensive disorder. We hypothesized that preeclampsia-associated EVs (PE-EVs) induced functional and phenotypic alterations of monocytes. First, we proved EV binding and uptake by THP-1 cells. Cellular origin and protein cargo of circulating PE-EVs were characterized by flow cytometry and mass spectrometry. An altered phagocytosis-associated molecular pattern was found on 12.5 K fraction of PE-EVs: an elevated CD47 "don't eat me" signal (p < 0.01) and decreased exofacial phosphatidylserine "eat-me" signal (p < 0.001) were found along with decreased uptake of these PE-EVs (p < 0.05). The 12.5 K fraction of PE-EVs induced significantly lower chemotaxis (p < 0.01) and cell motility but accelerated cell adhesion of THP-1 cells (p < 0.05). The 12.5 K fraction of PE-EVs induced altered monocyte functions suggest that circulating EVs may have a role in the pathogenesis of preeclampsia